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What are the Standards of PCB Gold Finger?

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Gold fingers on printed circuit boards (PCBs) are vital connectors used for linking the PCBs to external components, such as peripheral devices or other circuit boards. These gold-plated contacts provide a reliable and durable interface, ensuring consistent electrical connectivity. This article delves into the standards governing PCB gold fingers, discussing their design, materials, PCB manufacturing processes, applications, and quality control measures, backed by professional knowledge and data. PCB Instant Quote .my-button { display: inline-block; padding: 10px 50px; font-size: 16px; text-align: center; text-decoration: none; background-color: blue; color: #fffff0; border: none; border-radius: 5px; font-weight: bold; cursor: pointer; box-shadow: 0px 2px 5px rgba(0, 0, 0, 0.3); transition: background-color 0.3s ease, transform 0.3s ease; } .my-button:hover { background-color: #C23C30; transform: scale(1.05); } Definition and Functionality PCB gold fingers are the gold-plated connectors located along the edge of a PCB, commonly used in connectors like PCIe cards, memory modules, and other expansion cards. They serve as the contact points that interface with corresponding connectors in the devices they are plugged into, facilitating signal transmission and power distribution. What Is the Importance in PCB Design? The quality and durability of gold fingers are crucial for the overall performance and longevity of the device. Proper design and plating ensure low resistance and reliable contact, preventing data loss and ensuring smooth operation. What Are the Materials Used in Gold Fingers? Base Material: Copper The base material for gold fingers is typically copper, selected for its excellent electrical conductivity. The copper layer is etched to form the finger pattern and then plated with nickel and gold to enhance durability and performance. Material Electrical Conductivity Thermal Conductivity Role in PCB Copper High High Base layer for gold fingers Plating Layers: Nickel and Gold The copper fingers are coated with a layer of nickel followed by a layer of gold. The nickel layer acts as a barrier, preventing the diffusion of copper into the gold layer, which could degrade the contact quality. The gold layer provides excellent conductivity, corrosion resistance, and durability. Layer Thickness Range Purpose Nickel 3-6 µm Barrier layer, prevents copper diffusion Gold 0.5-1.27 µm (hard gold) Conductivity, corrosion resistance What Are the Types of Gold Used in PCB Gold Fingers Hard Gold Hard gold, also known as electrolytic gold, is commonly used for PCB gold fingers. It is an alloy of gold with other metals like cobalt or nickel, enhancing the wear resistance of the contact points. This type of gold plating is preferred for high-contact applications, such as connectors that will be frequently plugged and unplugged. Type of Gold Composition Properties Typical Use Hard Gold Gold alloy with nickel or cobalt High wear resistance, durability Gold fingers, connectors Soft Gold Soft gold, or pure gold, is used in applications requiring the highest conductivity and where the contacts will not be subject to significant mechanical wear. It is less common for gold fingers due to its lower durability compared to hard gold. Type of Gold Composition Properties Typical Use Soft Gold Pure gold Excellent conductivity, low durability Sensitive electronic components What Are the Standards for PCB Gold Finger Design? Dimensions and Tolerances The dimensions of gold fingers, including their length, width, and spacing, must adhere to specific standards to ensure compatibility with connectors. These standards are often dictated by the type of connector being used and the industry requirements. Parameter Standard Value/Range Description Finger Length Typically 1.0 - 2.0 mm Length of the contact area Finger Width Typically 0.5 - 1.0 mm Width of the contact area Finger Spacing Typically 0.5 - 1.0 mm Distance between adjacent fingers Plating Thickness The thickness of the gold and nickel layers is critical for ensuring adequate durability and conductivity. Standards specify minimum and maximum thicknesses to balance cost and performance. Layer Standard Thickness Purpose Nickel 3-6 µm Barrier and support layer Gold 0.5-1.27 µm (hard gold) Wear resistance, conductivity Edge Beveling To facilitate smooth insertion into connectors, the edges of the PCB at the gold fingers are often beveled. This chamfering process reduces the risk of damage to both the PCB and the connector. Feature Standard Angle Purpose Edge Beveling Typically 20-45 degrees Ease of insertion into connectors Manufacturing Process for PCB Gold Fingers Patterning and Etching The manufacturing process begins with patterning the copper layer on the PCB to form the finger outlines. This is typically done using a photolithographic process followed by chemical etching. Nickel Plating After the copper patterning, a layer of nickel is electroplated onto the gold finger areas. The nickel layer serves as a diffusion barrier and provides a robust base for the gold layer. Gold Plating Gold plating is applied over the nickel layer. The process involves immersing the PCB in a gold electrolyte solution and applying an electric current, which deposits a thin layer of gold onto the nickel surface. Quality Control and Testing The final step involves rigorous quality control to ensure that the gold fingers meet the required standards for thickness, adhesion, and electrical performance. This includes visual inspections, thickness measurements, and conductivity tests. Quality Control Standards and Testing Visual Inspection Visual inspection checks for defects such as uneven plating, scratches, or contamination that could affect the performance of the gold fingers. Thickness Measurement Non-destructive testing methods like X-ray fluorescence (XRF) are used to measure the thickness of the nickel and gold layers. This ensures compliance with industry standards and specifications. Test Method Purpose Standard Compliance X-ray Fluorescence (XRF) Thickness measurement Ensures plating meets required specifications Electrical Testing Electrical tests verify the conductivity and resistance of the gold fingers. These tests ensure that the contacts will perform reliably in their intended applications. Adhesion Testing Adhesion tests evaluate the bond strength between the gold, nickel, and copper layers. Poor adhesion can lead to delamination and failure of the contact points. What Are the Applications of PCB Gold Fingers? Consumer Electronics In consumer electronics, gold fingers are used in components such as memory modules, graphics cards, and expansion slots. Their reliability and durability are critical for ensuring consistent performance and user experience. Industrial and Military Applications In industrial and military applications, gold fingers are used in ruggedized connectors where environmental conditions can be extreme. The durability of gold plating is crucial for maintaining reliable connections in harsh conditions. Telecommunications In telecommunications, gold fingers are used in high-frequency connectors where signal integrity is paramount. The excellent conductivity and low contact resistance of gold fingers are essential for maintaining signal quality. What Are the Challenges in Gold Finger Manufacturing? Cost of Gold Gold is an expensive material, and the cost of gold plating can be significant. Manufacturers must balance the thickness of the gold layer with performance requirements to optimize cost and functionality. Environmental Concerns The plating process involves chemicals and heavy metals, raising environmental and safety concerns. Compliance with environmental regulations and adoption of eco-friendly practices are important considerations. Technical Limitations Achieving uniform thickness and coverage in gold plating can be challenging, especially for complex designs. Advances in plating technology and process control are continually being developed to address these challenges. What Are the Future Trends in Gold Finger Technology? Advanced Plating Techniques Innovations in plating techniques, such as pulse plating and selective plating, are being explored to improve the quality and efficiency of gold plating processes. These techniques can enhance the uniformity of the plating layer and reduce material consumption. Nano-Coatings and Surface Treatments Research into nano-coatings and advanced surface treatments aims to improve the performance of gold fingers. These treatments can enhance wear resistance, reduce contact resistance, and improve overall durability. Miniaturization and High-Density Applications As electronics continue to miniaturize, the demand for high-density connectors with smaller and more closely spaced gold fingers is increasing. This trend challenges manufacturers to achieve precise patterning and plating at smaller scales. Conclusion PCB gold fingers are a critical component in a wide range of electronic devices, ensuring reliable electrical connectivity. Adherence to established standards for design, materials, and manufacturing processes is essential for achieving high-quality and durable connectors. While challenges such as cost and environmental concerns exist, ongoing advancements in materials and technology promise to enhance the performance and sustainability of gold fingers in the future. References 1. IPC-, "Specification for Electroless Nickel/Immersion Gold (ENIG) Plating for Printed Circuit Boards," IPC, . 2. A. Hall, "The Complete PCB Design Guide," McGraw-Hill Education, . 3. J. H. Lau, "Advanced MEMS Packaging," McGraw-Hill Professional, . 4. M. H. Azarian et al., "Reliability of Electronic Components and Systems," Springer, . 5. K. C. Gupta et al., "Handbook of Flexible Electronics: Materials, Manufacturing, and Applications," Wiley, .

PCB Knowledge ⋅ 07/29/ 16:36

How to Understand Integrated Circuit Packaging Substrate Technology of PCB?

Integrated Circuit (IC) packaging progresses along with the development of integrated circuits. With the continuous development of various industries such as aerospace, aviation, machinery, light industry, and chemical industry, the entire machine also changes towards multi-function and miniaturization. Thus, it requires that the integration degree of IC becomes higher and higher, the functions become more and more complex. Correspondingly, it requires that the packaging density of integrated circuits becomes larger and larger, the number of leads becomes more and more, while the volume becomes smaller and smaller, the quality becomes lighter and lighter, and the upgrading becomes faster and faster. The rationality and scientificity of the packaging structure will directly affect the quality of integrated circuits. PCB Instant Quote .my-button { display: inline-block; padding: 10px 50px; font-size: 16px; text-align: center; text-decoration: none; background-color: blue; color: #fffff0; border: none; border-radius: 5px; font-weight: bold; cursor: pointer; box-shadow: 0px 2px 5px rgba(0, 0, 0, 0.3); transition: background-color 0.3s ease, transform 0.3s ease; } .my-button:hover { background-color: #C23C30; transform: scale(1.05); } Overview of IC Packaging Substrates Packaging Overview Traditional IC packaging uses lead frames as the conducting lines of IC and the carrier for supporting IC, which connects the pins on both sides or around the lead frame. With the development of IC packaging technology and the increase in the number of pins (more than 300 pins), the traditional QFP (Quad Flat Package) packaging form has restricted its development. Thus, in the mid-s, a new type of IC packaging form represented by BGA (Ball Grid Array) and CSP (Chip Scale Package) came out, and subsequently a necessary new carrier for semiconductor chip packaging was produced, which is the IC packaging substrate. Currently, the mainstream products of IC substrates according to their packaging methods include three types of substrates: BGA, CSP and FC (Flip Chip), with the latter two being the mainstream. The main functions of packaging: ① Isolate the exposed chip from the air to prevent the circuits on the chip from being corroded; ② Provide physical and mechanical support to prevent damage to the chip from external forces; ③ Between the highly refined chip and the less refined printed circuit board, a more refined packaging substrate is needed as an intermediate bridge for transmitting information. Packaging can generally be divided into five packaging levels. (1) Level 0 packaging: Refers to chips or wafers/dies that have not been packaged. (2) Level 1 packaging: Refers to the packaging of the substrate and the chip. (3) Level 2 packaging: Refers to the packaging structure of level 1 packaged onto the printed circuit board. (4) Level 3 packaging: Refers to the assembled system level. (5) Level 4 packaging: Refers to the connection between systems, such as the connection between computers. IC Packaging Technology Since around the s, electronic packaging has emerged from nothing, from transistor packaging to chip component packaging, from insert packaging to surface mount packaging, from metal packaging, ceramic packaging, metal-ceramic packaging to plastic packaging. Plastic packaging has a low cost, simple process, and is suitable for mass production. Therefore, it has strong vitality. Since its birth, it has developed faster and faster and occupied an increasing share in packaging. The manufacturing process of IC packaging technology can be divided into two major parts: The processes before plastic packaging are called the front-end processes, and the processes after forming are called the back-end processes. 1. Silicon Wafer Thinning The thickness of the chip brings certain difficulties to the division of the chip. Therefore, after the fabrication of the chip's circuit layer is completed, the backside of the silicon wafer needs to be thinned to the required thickness. A film (blue film) with a metal ring or plastic frame is attached to the backside of the chip to protect the chip's circuit before subsequent cutting. The backside thinning technologies of silicon wafers mainly include grinding, lapping, chemical polishing, dry polishing, electrochemical corrosion, wet corrosion, plasma enhanced chemical corrosion, atmospheric pressure plasma corrosion, etc. 2. Chip Cutting The process of separating each chip through wafer cutting is called chip cutting. The equipment used is called a cutting machine, also known as a dicing machine. Nowadays, cutting machines are all automatic, and the blades are generally pulsed lasers or diamond. Cutting is divided into partial cutting (not cutting all the way through, leaving a residual thickness) and complete cutting. Complete cutting generally has neat cutting edges and few cracks; for partial cutting, a thimble is used to apply force to completely separate the chips, so there will be more or less a small number of micro-cracks and grooves at the ports. Usually, the thinning process and chip cutting are usually combined to form two techniques: First, dicing before grinding (DBG). Before backside grinding, a certain depth of incision is made on the front side of the silicon wafer, and then grinding is performed. Second, dicing by thinning (DBT). Before thinning, a certain depth of incision is made by mechanical or chemical methods first, and then the grinding method is used to thin to a certain thickness. Finally, the remaining processing amount is removed by atmospheric pressure plasma corrosion technology. Both techniques can avoid or reduce the wafer warping caused by thinning and the edge damage caused by dicing, increasing the chip's anti-fragmentation ability. DBT can also remove the backside grinding damage of the silicon wafer and remove the micro-cracks and grooves caused by the chip. 3. Chip Mounting Chip mounting, also known as chip bonding, is the process of fixing the chip on the packaging substrate or the pin frame carrier. The equipment for chip mounting is called a mounter. The main methods of chip mounting can be divided into four methods: eutectic bonding method, soldering bonding method, conductive adhesive bonding method and glass adhesive bonding method. 1) Eutectic Bonding Method Eutectic reaction refers to the reaction in which a liquid of a certain composition simultaneously crystallizes two solid phases of a certain composition at a certain temperature. The point at which the reaction begins is called the eutectic point. The two solid phases generated are mechanically mixed together to form a basic structure with a fixed chemical composition, and are collectively referred to as eutectics. Place the chip on the chip carrier of the ceramic substrate that has been plated with a gold film. Under a certain pressure (friction or ultrasound), with nitrogen as the protective gas, heat it to the eutectic point temperature. When the temperature is higher than the eutectic temperature, the gold-silicon alloy turns into a liquid Au-Si eutectic melt. After cooling, when the eutectic melt changes from the liquid phase to a mechanical mixture in the form of grains combined with each other - the gold-silicon eutectic melt and solidifies completely, a firm ohmic contact is thus formed, that is, eutectic bonding. 2) Soldering Bonding Method Soldering bonding method is a process method for chip bonding using alloy reactions. Its process flow is to deposit a certain thickness of gold or nickel on the backside of the chip in a hot nitrogen atmosphere, deposit a metal layer of gold-palladium-silver or copper on the pad of the solder pad, and solder the chip on the pad with a lead-tin alloy solder. The alloy solder can be divided into hard solder and soft solder. 3) Conductive Adhesive Bonding Method Conductive adhesive is an adhesive that has certain conductive properties after curing or drying. It usually consists mainly of matrix resin (such as epoxy resin) and conductive filler, that is, conductive particles (such as silver powder). The conductive particles are combined together through the bonding effect of the matrix resin to achieve the conductive connection of the material. The conductive particles play a conductive role, while the matrix resin plays a bonding role. The thermal expansion coefficient of the polymer resin is similar to that of the copper pins. The conductive adhesive method is a commonly used chip bonding method in packaging. Conductive adhesives are divided into paste conductive adhesives and solid films. Paste conductive adhesive: Place the chip precisely on the chip pad where the conductive adhesive (binder) is applied to the appropriate thickness and contour with a syringe or injector for curing. Solid film: Cut it to the appropriate size and place it between the chip and the base pillar, and then perform thermocompression bonding. The use of solid film conductive adhesive can enable automated large-scale production. 4) Glass Adhesive Bonding Method Glass adhesive is similar to conductive adhesive. It is made by mixing conductive metal powder, low-temperature glass powder and organic solvent into a paste. When using glass adhesive bonding, the glass adhesive is applied to the chip seat of the substrate by stamping, screen printing, dispensing and other methods, the chip is placed on the glass adhesive, and the substrate is heated to above the glass melting temperature to complete the bonding. Because the temperature for completing the bonding is higher than that of the conductive adhesive, it is only applicable to ceramic packaging. 4. Chip Interconnection Chip interconnection is to connect the chip's bonding area with the I/O leads of the electronic packaging shell or the metal bonding area on the substrate. Common chip interconnection methods include wire bonding (WB), flip chip bonding (FCB) and tape automated bonding (TAB). The limitations of the three connection technologies for different packaging forms and the integration degree of integrated circuit chips have different application scopes: Wire bonding is suitable for 3 to 257 leads; Tape automated bonding is suitable for 12 to 600 pins; Flip chip bonding is suitable for 6 to 16,000 pins. Therefore, flip chip bonding is suitable for high-density assembly. 1) Wire Bonding Process Technology Wire Bonding (WB) process technology is a process technology that uses high-purity metal wires to bond the internal circuit of the chip before packaging and the I/O leads of the microelectronic packaging or the metal wiring bonding area (pad) on the substrate. Ensuring the external electrical interconnection of the chip and the packaging substrate, and the smooth input/output is an important step in the packaging process. Wire bonding technology can be divided into ultrasonic bonding, thermocompression bonding and thermosonic bonding. The connecting wires include: gold wire, aluminum wire and copper wire. Among them, gold wire has the advantages of good corrosion resistance, strong toughness, high electrical conductivity and good thermal conductivity, so it is widely used; Aluminum wire is not suitable for forming solder balls due to easy oxidation when heated, and its toughness and heat resistance are not as good as gold wire. At the same time, the elongation fluctuation of aluminum wire is large, and the performance of the same batch of products varies greatly; Copper wire has low cost, high strength, good electrical conductivity and strong thermal conductivity, but its corrosion resistance is weak, and the pressure required for bonding is large, which is easy to damage the chip. To sum up, gold wire is currently the most ideal bonding wire. After the chip is connected to the packaging substrate through the bonding lead, and then precisely covered with a special protective organic material to isolate it from the outside, it has high stability and oxidation and corrosion resistance. At present, the evaluation of whether WB is good mainly through tensile test and ductility test. Taking gold wire as an example, a fixed-length gold wire is selected, both ends are fixed, and it is pulled at a stable speed to read the extended length when it is pulled off and the force applied when it is pulled off. The WB process is simple and low-cost, and is currently the most widely used packaging form. 2) Tape Automated Bonding Technology Tape, that is, a ribbon carrier, refers to a lead frame formed by etching the copper foil on the ribbon-shaped insulating film. Tapes are generally made of PI and are provided with feed holes unified with the specifications of film at both sides. Tape automated bonding technology refers to a process technology that uses the metal foil wire of the spider-shaped lead image to interconnect the chip bonding area with the I/O of the electronic packaging shell or the metal wiring bonding area on the substrate. Its manufacturing process: First, complete the conductor pattern of the component pins on the polymer, then place the wafer on it corresponding to its bonding area, and finally perform batch bonding of all leads through the hot electrode at one time. As shown in Figure 7-5 is the physical picture of the TAB substrate. The key technology of TAB is the chip bump technology. The surface of the IC chip is plated with a passivation protection layer, which is thicker than the electroplated bonding point. Therefore, it is necessary to first grow a bonding bump at the bonding point of the chip or the front end of the inner lead of the TAB tape before subsequent bonding. Generally, TAB tape technology is divided into bumped tape and bumped chip. Advantages of TAB technology compared with WB technology: (1) The bonding plane of TAB leads is low, and its structure is light, thin, short, small, and the height is < 1mm. (2) The electrode size of TAB, and the distance between the electrodes and the bonding area are smaller than those of WB. (3) Correspondingly, more I/O pins can be accommodated, and the installation density is higher. (4) The R, C and L of the leads of TAB are smaller than those of WB, the speed is faster, and the high-frequency characteristics are better. (5) TAB interconnection can be used for electrical aging, screening and testing of IC chips. (6) TAB uses Cu foil leads, which have good heat and electricity conductivity and high mechanical strength. (7) The bonding pull force of TAB solder joints is 3 to 10 times higher than that of WB. (8) The size of the tape can be standardized and automated, which can be produced on a large scale to improve efficiency and reduce costs. 3) Flip Chip Process Technology Flip Chip (FC) refers to interconnecting components directly to the substrate through solder balls on the chip with the component facing upwards, and it can also be called DCA (Direct Chip Attach). The main methods for making its bumps include evaporation/sputtering bump fabrication method, electroplating bump fabrication method, ball placement and template printing solder bump fabrication method. Flip chip (abbreviated as FC) refers to directly interconnecting the component upward to the substrate through solder balls on the chip, and it can also be called DCA (direct chip attach). The main methods for fabricating its bumps include evaporation/sputtering bump fabrication method, electroplating bump fabrication method, ball placement and stencil printing for solder bump fabrication method. The chip in WB packaging is facing upward, while the chip in FC packaging is facing downward. The solder areas on the chip are directly interconnected with the solder areas on the substrate. Therefore, the interconnects in FC technology are very short; the stray capacitance, interconnect resistance, and interconnect inductance generated are much smaller than those in WB, making it more suitable for high-frequency and high-speed electronic products; chip installation and interconnection can be carried out simultaneously, with a simple and fast process; in FC packaging, the area occupied by the chip is small, so the installation density of the chip increases, greatly increasing the number of I/Os, and the integration and interconnection are greatly improved. However, the FC packaging installation and interconnection process is difficult, the chip is facing downward, and solder joint inspection is difficult; the bump process is complex and costly; at the same time, its heat dissipation effect is low and needs to be improved. 5. Molding Technology The technology of packaging the chip and lead frame after the chip interconnection is completed is called molding technology. Molding technologies include metal packaging, plastic packaging, ceramic packaging, etc. However, considering the cost and other aspects, plastic packaging is the most common packaging method, occupying about 90% of the market. The molding technologies of plastic packaging include transfer molding, inject molding, pre-molding, etc. Currently, transfer molding technology is mainly used. The materials used in transfer molding technology are generally thermosetting polymers. The thermosetting plastic molding process is a combination of "hot runner injection molding" and "pressure molding". In the traditional hot runner injection molding, a certain temperature is maintained in the melt cavity. Under the action of external pressure, the clinker undergoes chip molding and obtains a certain chip shape in the mold cavity. 6. Deburring and Flash Removal The phenomenon of flash and burr refers to the overflow of plastic resin, tape burrs, lead burrs, etc. in plastic packaging. The main process flow for deburring is: medium deburring and flash removal → solvent deburring and flash removal → water deburring and flash removal. Medium deburring and flash removal: Flushing the module with abrasive materials (such as granular plastic balls) together with high-pressure air. During this process, the medium will slightly abrade the surface of the frame pins, which is helpful for the adhesion of solder and the metal frame. Solvent deburring and flash removal: Usually only suitable for very thin burrs. Solvents include N-methylpyrrolidone (NMP) or dimethylfuran (NMF). Water deburring and flash removal: It is to impact the module with high-pressure water flow. Sometimes abrasive materials are used together with high-pressure water flow. 7. Trim and Form The trim and form process refers to cutting the dams between the leads outside the frame and the connected areas on the frame tape, and bending the leads into a certain shape to meet the assembly requirements. The trim and form process is divided into two procedures and can be completed mechanically at the same time. First, the trimming is done, then the solder is applied, and then the forming process is carried out. The advantage is that the cross-sectional area without solder application, such as the area of the incision, can be reduced. 8. Marking Marking is the printing of indelible and clear marks on the top surface of the packaged module, including the manufacturer's information, country, period code, etc. The two most commonly used marking methods are ink marking and laser marking. Ink marking: Using rubber to engrave the marking. Ink is a polymer compound and requires thermal curing or UV curing. Ink marking has higher requirements on the surface. If the surface is contaminated, the ink cannot be applied. Laser marking: Using a laser to write marks on the module surface. The biggest advantage of laser marking is that the marking is not easy to erase and the process is simple; the disadvantage is that the handwriting is relatively light. 9. Solder Application Solder application on the external leads of the frame after packaging is to apply a protective layer on the frame pins and increase their solderability. Currently, there are mainly two methods for solder application: electroplating and dip soldering. Electroplating process flow: Cleaning → Electroplating in the electroplating tank → Rinsing → Blowing dry → Drying (in the oven). Dip soldering process flow: Deburring → Degreasing → Removing oxides → Dipping flux → Hot dip soldering → Cleaning → Drying. Dip soldering is prone to uneven coating, thick in the middle and thin on the edges (caused by surface tension), while electroplating is thin in the middle and thick especially at the corners (caused by charge accumulation effect). Electroplating solution can also cause particle contamination. A New Packaging Technology - Embedded Chip Technology Embedded chip technology refers to a process technology that embeds the chip into the packaging substrate and then performs pattern electroplating to interconnect the chip and the substrate lines. Embedded technology is classified according to different pad connection methods and via connection methods. 1. Advantages of Embedded Chip Technology 1) Enabling higher density or miniaturization of the system Conventional chips are mounted on the surface of the packaging substrate, and all signal connections are designed and arranged on the PCB surface pads. The system packaging formed by embedding the chips inside the packaging substrate will significantly shorten and reduce the connection points, wires, pads, and vias, thus having greater integration, flexibility, and adaptability. 2) Improving the reliability of system functions Embedding the chips inside the packaging substrate and isolating them from the "atmosphere" environment enables these chips to receive the most effective protection; at the same time, due to the position of these chips embedded inside the printed circuit board and having the shortest wire (or via) connection, the failure rate of "connections" is eliminated and reduced. 3) Improving the performance of signal transmission Since the chips are isolated from the atmosphere and receive the best protection, the signal transmission is more stable; the shortening or reduction of connection wires, pads, and vias ensures the integrity of signal transmission. 4) Entering the market faster and reducing production costs Chip and substrate production occurs simultaneously at the same location, reducing transportation, storage, and management processes, as well as reducing "repeated" inspection and review steps. The shortened production cycle enables faster market entry and lower costs, enhancing the competitiveness of the product in the market. 2. Disadvantages of Embedding Active Components Between Substrates The disadvantages of embedding active components between substrates are as follows: (1) The manufacturing process of the packaging substrate, which is the traditional packaging carrier, needs to undergo significant changes, so many existing packaging substrate manufacturers have difficulty adapting to this transformation. (2) For printed circuit board factories, due to production efficiency and economic benefits constraints, they cannot guarantee that the products embedding active components are completely qualified. In this regard, the top priority is to establish a set of design, inspection and measurement methods and standards. (3) There are many issues that need to be addressed in the industrial structure, such as the need to establish a system for supplying chips from multiple manufacturers, etc. 3. Types of Embedded Chip Technology Embedded chip technology can be divided into: embedding the chip first and then fabricating the substrate, embedding the chip halfway, and embedding the chip at the end. Figure 7-1l shows the schematic diagram of the embedded chip structure. First, the chip is attached to the semi-finished substrate, then resin is poured between the chip and the substrate through lamination, and the chip line and the substrate line are conducted through pattern electroplating. Finally, the substrate line is continued to be fabricated. This technology can greatly reduce the total thickness of the packaging substrate and the chip, and has better reliability. The technology of embedding the chip requires very mature packaging substrate fabrication technology. Once there is scrap, the chip will also be scrapped simultaneously. Reference He Wei, PCB Basic Electrical Information Science and Technology, China Machine Press，126-133

PCB Knowledge ⋅ 07/11/ 17:39

What Are the Status, Classification, and Characteristics of Special PCB？

Overview In , the Electronic Information Products Management Division of the Ministry of Information Industry (now the Ministry of Industry and Information Technology) summarized high-end PCB product types as HDI boards, multi-layer FPCs, rigid-flex boards, IC substrates, communication backplanes, special material PCBs, and new types of PCBs. However, there is still no complete definition of special printed circuit boards in the field of PCB design and manufacturing. The general consensus is that special printed circuit boards refer to those with unique manufacturing materials, special product applications, and distinctive manufacturing processes. The specialization of materials for special printed circuit boards is determined by their functions and performance requirements in electronic equipment. The substrate material acts as a carrier for PCB traces and components. With the increasing frequency and speed of electronic signal transmission and the rise in layer counts, low electromagnetic interference, high signal integrity, and high heat dissipation have become essential qualities for new products. These performance requirements can no longer be met by circuit design alone, making the selection of new materials a key direction for technological progress. For high-frequency signal transmission and high-current transmission applications, low dielectric constant, low loss, and high thermal conductivity materials are used as substrate materials for special printed circuit boards. The choice of these unique substrate materials determines the specialized manufacturing processes. PCB Instant Quote .my-button { display: inline-block; padding: 10px 50px; font-size: 16px; text-align: center; text-decoration: none; background-color: blue; color: #fffff0; border: none; border-radius: 5px; font-weight: bold; cursor: pointer; box-shadow: 0px 2px 5px rgba(0, 0, 0, 0.3); transition: background-color 0.3s ease, transform 0.3s ease; } .my-button:hover { background-color: #C23C30; transform: scale(1.05); } With the widespread use of electronic products in daily life, industrial production, and scientific innovation, special printed circuit boards are increasingly being used in fields such as communication electronics, consumer electronics, automotive electronics, instruments, and power supplies. According to statistics from WECC (World Electronic Circuit Council), IPC (Association Connecting Electronics Industries), and CPCA (China Printed Circuit Association): 1. In , the global PCB output value was $50.9 billion, with special boards accounting for $2.3 billion, or 4.5% of the total. 2. In , China's PCB output value was 170 billion RMB, with special boards accounting for about 10.2 billion RMB, or 6.0% of the total. What Is Metal Core PCB Manufacturing Technology？ As electronic products develop towards being lighter, thinner, smaller, higher in density, and more multifunctional, the design linewidth of printed circuit boards becomes finer, the copper area smaller, the spacing between components closer, and the assembly density and integration higher. Power consumption increases, making thermal management solutions increasingly important, and the need for improved thermal conductivity of PCB substrates more urgent. Poor thermal conductivity of the substrate leads to slower heat dissipation, causing components on the PCB to overheat, which can result in component aging, failure, shortened lifespan, and reduced reliability of the entire system. One solution to this problem is the use of metal core printed circuit boards. What Is Overview of Metal Core PCB？ Metal core printed circuit boards (MCPCBs) consist of a metal substrate with excellent thermal conductivity, an insulating dielectric layer, and a copper trace layer, forming a high-thermal-conductivity PCB with a sandwich structure as shown in Figure 3-1. The demand for high-frequency communication signals, high-definition, and large data transfer has driven continuous innovation in PCB manufacturing technology. High-frequency and high-speed signal transmission requires strict material standards, ensuring not only the creation of metal traces on an insulating substrate for connectivity but also the quality of signal transmission. In fields such as microwave applications and high-power electronics (e.g., LED applications), the thermal properties of materials significantly impact system reliability. In high-reliability, high-power, high-frequency applications such as military radars, microwave applications, missile control systems, and GPS power amplifiers, conventional thermal management methods are inadequate, making materials with good thermal conductivity a necessity. Practical applications have shown that using metal substrates for thermal solutions, as opposed to traditional heat sinks and fans, can greatly reduce equipment size and manufacturing costs. For MCPCBs with a three-layer sandwich structure, the material selection and manufacturing processes for each layer are unique. The metal substrate layer can theoretically be any metal with good thermal conductivity, but due to cost and manufacturability constraints, common materials include aluminum, iron, copper, invar, and tungsten-molybdenum alloys. This layer provides physical support and a thermal pathway for the circuits and components. Among these, aluminum is favored for its abundant resources, mature manufacturing processes, relatively low cost, good thermal conductivity, ease of processing, and environmental friendliness. Aluminum-based PCBs offer advantages such as economical material costs, reliable electronic connections, high thermal and mechanical strength, and lead-free soldering, making them a key focus of research and application. The insulating dielectric layer typically uses modified epoxy resins, polyphenylene ether (PPE), or polyimide (PI). Its primary function is to prevent short circuits between the trace layer and the metal substrate. The trace layer, created by etching copper foil, is the main unit for electrical signal and current transmission on the PCB. High thermal conductivity MCPCBs have developed various types, including planar thick copper-based PCBs, aluminum-based PCBs, aluminum core double-sided PCBs, planar copper-based PCBs, aluminum cavity PCBs, metal block-embedded PCBs, and flexible aluminum-based PCBs, which are widely used in consumer electronics, automotive, military, aerospace, and other fields. The key to their performance lies in the adhesive properties between the metal substrate and the circuit layer. What Are Material Properties and Structure of Metal Core PCB? Material Characteristics of Metal Core PCBs It is well known that the thermal conductivity of metal materials is significantly higher than that of synthetic resin materials (and the dielectric they form). This is the theoretical basis for using metal materials as PCB substrates to address the performance degradation of high-heat electronic components. However, metal materials have the disadvantage of high density, making metal core PCBs heavier than organic-based PCBs of the same specifications. What Are Types, Structures, and Performance of Metal Core PCBs? Types of Metal Core Copper Clad Laminates Metal core copper clad laminates (MCCLs) are the base materials for manufacturing metal core PCBs. Their structure and manufacturing methods are similar to those of conventional organic resin-based copper clad laminates (CCLs). MCCLs generally consist of three layers: a copper foil layer, an insulating layer, and a metal layer (such as copper, aluminum, iron, steel, invar, tungsten-molybdenum alloy). Based on the type of metal used, MCCLs can be classified into aluminum-based CCLs, copper-based CCLs, iron-based CCLs, and tungsten-molybdenum alloy CCLs, with aluminum-based, copper-based, and iron-based CCLs being the most widely used. 1. Aluminum-Based Substrates: Commonly used aluminum materials include LF, LAM, and LY12, meeting the national aluminum alloy manufacturing standards GB/T-. Performance requirements include tensile strength of 294 N/mm², elongation of 5%, and thermal conductivity of 150-210 W/(m·K). Common thicknesses are 1.0 mm, 1.6 mm, 2.0 mm, and 3.2 mm. 2. Copper-Based Substrates: Typically use red copper sheets, meeting national standards GB/T-, with performance requirements including tensile strength of 245-217 N/mm², elongation of 15%, and thermal conductivity of 403 W/(m·K). Common thicknesses are 1.0 mm, 1.6 mm, 2.0 mm, 2.36 mm, and 3.2 mm. 3. Iron-Based Substrates: Generally use cold-rolled steel plates or low-carbon steel plates, with performance requirements of 25-32 kg·F/mm² tensile strength and 15% elongation. Common thicknesses include non-phosphorous 1.0 mm and 2.3 mm types, and phosphorous iron bases with 0.5 mm, 0.8 mm, and 1.0 mm thicknesses. Performance Comparison of Common Metal Substrates The three main types of metal substrates used in industrial manufacturing are copper, iron, and aluminum substrates, with their performance compared as follows: 1. Copper Substrates: Excellent thermal conductivity, used for heat conduction and electromagnetic shielding, but heavy and expensive. 2. Iron Substrates: Best for electromagnetic interference shielding but with slightly poorer thermal conductivity and cheaper. 3. Aluminum Substrates: Good thermal conductivity, lightweight, decent electromagnetic shielding, but poor resistance to salt corrosion. Aluminum-based CCLs are currently the most widely used metal substrates due to their superior electrical performance, thermal conductivity, electromagnetic shielding, high voltage resistance, and bendability. Aluminum-based PCBs are extensively used in high-power LED lighting, power supplies, TV backlights, automotive, computers, air conditioner inverters, avionics, medical equipment, audio, and even as essential components in commonly used smartphone cameras. Functions and Performance of Insulating Layers, Metal Layers, and Conductor Layers in Metal Core PCBs 1. Insulating Layer Performance The insulating layer in metal core PCBs uses organic polymers (e.g., PET, modified PPE, modified epoxy resins, PI), metal oxides (e.g., Al₂O₃), or ceramics. Its function is to isolate electrical signals between the traces and bond the copper foil layer to the metal layer, providing insulation and adhesion. The typical thickness of the insulating layer in metal core PCBs is 50-200 µm. It is placed between the metal substrate and the copper foil layer, requiring strong adhesion to both. If the layer is too thick, it provides good insulation, preventing short circuits with the metal Characteristics and Functions of the Metal Layer in Metal Core PCB Using a metal core substrate (IMS) or metal core printed circuit board aims to enhance the heat dissipation of the entire board after mounting heat-generating components, thereby improving the thermal reliability and lifespan of electronic products. The primary functions of the metal layer in the metal substrate are as follows: 1. Heat Conduction in PCB: During processing, especially during use, printed circuit boards generate significant heat, causing a localized "heat island" effect. This creates substantial internal stress within the board, damaging its internal structure and affecting the performance of electronic products, becoming a major factor in failure. Since the thermal conductivity of metal is higher than that of the PCB dielectric layer, adding a metal plate (on the surface, inside, or both) to the PCB creates a "cold finger" effect. This forms a rapid heat transfer channel within the PCB, lowering the overall board temperature and quickly equalizing it, thus reducing internal stress. Practical evidence shows that products using metal substrates can lower the overall board temperature by 30-50°C compared to organic substrates of the same specification in high-heat environments. 2. Providing Rigidity and Controlling the Coefficient of Thermal Expansion (CTE): The electronic components mounted on PCBs are typically attached via soldering or surface mounting, necessitating a rigid support, which is one of the advantages of rigid-flex PCBs. Metal materials, with their high heat resistance, ductility, high thermal conductivity, and CTE similar to that of copper, meet the need for controlling deformation or size and enhancing reliability during the PCB's operation, when the dielectric layer made of fiberglass and resin may soften or deform due to heat. 3. Acting as a Shield: Metal materials provide superior electromagnetic shielding compared to organic synthetic resins. PCBs in electronic devices are exposed to numerous signal interferences from all directions in the atmosphere, affecting internal signal transmission and the reliability of received signals. Adding a metal layer on the surface or inside the PCB acts as a shield, significantly improving signal transmission or reception integrity. Additionally, the metal substrate can serve as a grounding layer, further enhancing product quality. Conductive Layer (Copper Foil Layer) Performance in Metal Core Substrates The conductive layer of metal core substrates is etched from the copper foil layer of the copper-clad laminate. Therefore, the performance of the copper foil in the metal core copper-clad laminate directly affects the performance of the metal core PCB. To enhance the bonding strength between the copper foil and the insulating layer, the back of the copper foil undergoes chemical oxidation, zinc plating, and brass plating processes. These procedures aim to increase peel strength and insulation properties. The typical thicknesses of copper foil layers are 17.5 µm, 35 µm, 75 µm, and 140 µm. In aluminum-based PCBs used in communication power supplies, the commonly used copper layer thickness is 140 µm. Reference He Wei, PCB Basic Electrical Information Science and Technology, China Machine Press，322-326

PCB Knowledge ⋅ 07/05/ 17:29

1. Flex PCB Soldering Correct Temperature

The general rule is that you should never use rigid PCB temperature profiles to reflow flex PCBs. That is because these temperatures are likely to be much higher than flexible PCBs can tolerate.

Excessive heat during flex PCB soldering can lead to blistering and delamination. Where you do not know the proper reflow temperature profiles for flexible PCBs, it is best to seek guidance from a reputable PCB manufacturer. 

The typical single-sided flex joint requires a reflow temperature of 330 – 400°C. Generally, it is best to stick to the minimum temperature to minimize the chances of damage due to exposure to heat.

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2. Monitor Heat Release During Assembly

A flexible circuit board is considerably thin, so heat control is essential. But that is not the only reason. In all electrical devices, excessive heat is a legitimate cause for concern. Electrical appliances that do not release heat well can be dangerous. You may have heard that the cell battery exploded due to overheating.

Flexible circuit boards are electrical conductors. Engineers and designers must thus come up with a way to dissipate that heat. Failure to do so can lead to the outright destruction of the delicate circuitry in flexible PCBs.

So what do you do during flex PCB soldering and assembly to ensure that a flexible circuit board dissipates heat well? Well, you need to go for components that have an exceptional surface-to-volume ratio. Stick to compact designs to shorten the thermal path. This way, there is less heat buildup. 

3. Avoid Stacking Conductors On Multiple Layer Boards 

Many times during flex PCB soldering and assembly, manufacturers signal and return lines over each other. They do so on adjacent layers to reduce electromagnetic interference (EMI). It makes the overall flexible circuit thicker, which creates an I-beam effect. 

If you are going to use this method of EMI reduction, ensure that you stagger all the line pairs to reduce this I-beam effect. 

Contact us to discuss your requirements of FPC/PCB Pumice Line. Our experienced sales team can help you identify the options that best suit your needs.

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4. Remove Flex PCB Soldering Residue

Many beginners find this part of the flex PCB soldering challenge. The truth is soldering small contacts can be difficult. With practice, however, things should get more comfortable.

There are different techniques you can use when soldering the accelerometer. In this section, we will look at how to solder the accelerometer using rosin-core solder and soldering iron

In this technique, you will be using a flux pen during flex PCB soldering. The flux does several essential things. It cleans the surface oxides and etches them, averts oxidation of copper after heating, and boosts the flow of solder. Flux lowers the surface tension of the weld, ensuring that molten solder spreads and penetrates readily.

Always make sure that you use a small amount of solder paste onto the solder pad and accelerometer contact. Thoroughly clean the solder iron tip before quickly bringing it into contact with the accelerometer and substrate pad. The solder joint should form instantly. If it does not, dispense some more solder paste. Make sure that the paste bridges onto the pad from the copper solder. Dab the joint with the solder iron tip.

5. Soldering the SMT Resistors and Capacitors

Solder paste usually comes in large syringes or jars, so be sure to purchase a smaller needle that has the appropriate gauge tip. To solder SMT resistors and capacitors in place, follow the following steps:

• Start by cleaning the copper solder pads using the flux pen
• Dispense a little solder paste onto the capacitor pads
• Release the capacitors you require from the tape real
• Gently place the capacitor on top of the copper solder pads
• Tin the solder iron’s tip and clean it using a wet sponge
• Touch the solder pad and capacitor using the tip of the soldering iron

6. Checking Continuity and Sensor Outputs

This crucial step of the flex PCB soldering process can prove challenging for beginner PCB manufacturers. However, it’s quite straightforward once you get used to it. 

The first thing you need to do is check for continuity in the solder joints using a multi-meter. See whether there’s contact from the connector side to the accelerometer chip. Next, check for any shorts between the PCBs solder pads. See if there’s continuity from the copper traces to the adjacent contacts on the accelerometer. 

7. Cleaning Off Flux/Rosin Residue

The flexible printed circuit board (PCB) is a version of PCBs that have unique capabilities. Besides offering the same features of an ordinary PCB such as repeatability, high density, and reliability, flex PCBs have the flexibility and higher vibration resistance. These PCBs can assume three-dimensional configurations.

The flex PCB soldering process also involves cleaning off the flux or rosin residue from the solder joints. Of course, if you’re using a no-clean flux, then you may not need to worry about cleaning off any flux residue. Otherwise, the waste can corrode the solder joints and result in issues after a while. Don’t forget to place electric tape over the front side of the traces.

8. Prevent Bending of Flex PCB Soldering

Here, you can use either carpet tape or double-back scotch tape, as well as an overhead transparency film. 

Laminating the backside of the flex circuit helps reduce the concentration of stress at the edges of the accelerometer and connector. This stress concentration could cause fatigue and eventual failure of copper traces. 

To prevent solder joints from flexing, try placing a thicker stiffener close to the solder joints of the accelerometer. Given that there’s more stress concentration at each solder joint, it’s best to opt for a thicker stiffener, mainly if there’ll be active flexing on the accelerometer.

9. Potting Solder Joints

You’ll probably need to pot the solder joints as part of the flex PCB soldering process. Potting helps prevent solder joints from flexing. Dab 5-minute epoxy on the edges of the accelerometer to do so.

Keep in mind, however, that there may be a concentration of mechanical stress at the edge of the potting area. Some solder joints create electrical connections. Such solder joints also create high-stress levels that may lead to mechanical fatigue failures.

10. Flexibility for Stiffeners

Usually, flexible circuitry becomes evident during the processes of copper plating, pumice scrubbing, or etching. The exposure of this circuitry can cause dimensional changes. The design of flexible electronics, as we pointed out earlier, needs a significant amount of tolerance to allow for cover films and stiffeners. 

As you consider cover films, don’t forget to take out the adhesive squeezing after the lamination of the film dielectric. If you don’t do so, the processes of fabrication and inspection become harder. 

Summary

Printed circuit boards are famous for how versatile they are. They’re easy to fold, bend, and twist into the configurations you desire. The process of flex PCB soldering, however, can be quite complicated. To get everything right, manufacturers must understand the design rules of these circuits.

Are you looking for top quality flex PCBs for your electronic products? Talk to us at WellPCB today. We have extensive experience in the assembly of all kinds of printed circuit boards. Check out our tailor-made solutions today.

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