Three Categories of PCB Reinforcement Materials
PCB circuit boards are crucial for machinery and electrical equipment, serving as essential carriers for software development. Different types of machinery and equipment use various PCB materials. Rigid printed circuit boards (RPCB) can be categorized into several types. Common PCB reinforcement materials generally fall into the following three categories:
1. Phenolic PCB Paper Substrate
This type of PCB board consists of paper pulp and wood pulp, sometimes including cardboard, V0 board, flame-retardant board, and 94HB. Its primary material is wood pulp fiber paper, which is pressed and bonded with phenolic resin. Phenolic paper substrates are not fireproof, can be punched, are cost-effective, and have a low relative density. Examples include XPC, FR-1, FR-2, FE-3, etc., with 94V0 being a flame-retardant version.
2. Composite PCB Substrate
These boards incorporate wood pulp fiber paper or cotton pulp fiber paper as reinforcement, combined with glass fiber cloth as surface reinforcement. Both materials are bonded with flame-retardant epoxy resin. Notable examples are single-sided half-glass fiber 22F, CEM-1, and double-sided half-glass fiber board CEM-3, with CEM-1 and CEM-3 being the most common composite base copper-clad laminates.
3. Glass Fiber PCB Substrate
Sometimes epoxy boards, glass fiber boards, FR4, and fiber boards are used. Epoxy resin serves as the binder, while glass fiber cloth acts as the reinforcing material. This type of circuit board offers high working temperatures and is unaffected by environmental factors. Often utilized in double-sided PCBs, it is more expensive than composite PCB substrates, with a common thickness of 1.6 mm. Suitable for power supply boards, high-level circuit boards, and widely used in computers, peripheral equipment, and communication devices.
Three Reasons for Aging of Solder Joints in PCBA Processing
**Failure Modes of Solder Joints**
The reliability tests of PCBA processing solder joints include both reliability testing and specific analysis. The primary goal is to evaluate the reliability of integrated circuit chip electronic components and provide data parameters for the reliability design of the entire equipment. Additionally, it aims to enhance the reliability of solder joints through specific analysis of failures to find failure modes and causes. This process is crucial for improving and optimizing design processes, structural parameters, and welding techniques. Analyzing failure modes based on cycle life predictions is essential for creating mathematical analysis models. The following are three detailed failure modes.
1. **Solder Joint Failure Caused by Welding Process**
Objective conditions during welding and subsequent cleaning processes may lead to solder joint failures. SMT solder joint reliability issues primarily arise from production, installation, and usage stages. During production and installation, limitations in equipment and human errors in welding specification selection often lead to issues like false welding, solder short circuits, and other defects. In the usage stage, collisions and vibrations can cause mechanical damage, while thermal stress due to large temperature differences can lead to stress cracks. Additionally, gold and silver corrosion may occur in thick and thin film hybrid circuits due to reactions between solder materials and gold or silver-plated pins, reducing solder joint reliability. Excessive ultrasonic cleaning can also negatively impact reliability.
2. **Failure Caused by Aging**
When molten solder interacts with a clean substrate, intermetallic compounds (IMCs) form at the interface. During aging, the solder joint’s microstructure coarsens, and the IMC layer continues to grow. The failure of solder joints partly depends on the growth kinetics of the IMC layer. Although IMCs indicate good welding, excessive thickness can lead to micro-cracks or breakage in the solder joint. When the thickness surpasses a critical point, the IMCs become brittle. Due to thermal expansion mismatches between materials, solder joints experience strain during usage, potentially causing failure. Studies show that adding trace amounts of lanthanum to Sn60/Pb40 solder alloy reduces IMC thickness, doubling the thermal fatigue life and significantly improving solder joint reliability.
3. **Failure Caused by Thermal Cycling**
During usage, power supply circuit interruptions and temperature fluctuations subject solder joints to thermal cycling. The thermal expansion mismatch between packaging materials induces stress and strain in solder joints. For SMT, the coefficient of thermal expansion (CTE) of A1203 ceramic is 6 × 10^-6 °C^-1, while that of epoxy resin/glass fiber substrate is 15 × 10^-6 °C^-1. Temperature changes cause corresponding stress and strain in solder joints, generally between 1% to 20%. In THT processes, flexible pins absorb most of the strain, but in SMT, solder joints bear the strain, leading to crack initiation and eventual failure.
PCB circuit boards are crucial for machinery and electrical equipment, serving as essential carriers for software development. Different types of machinery and equipment use various PCB materials. Rigid printed circuit boards (RPCB) can be categorized into several types. Common PCB reinforcement materials generally fall into the following three categories:
1. Phenolic PCB Paper Substrate
This type of PCB board consists of paper pulp and wood pulp, sometimes including cardboard, V0 board, flame-retardant board, and 94HB. Its primary material is wood pulp fiber paper, which is pressed and bonded with phenolic resin. Phenolic paper substrates are not fireproof, can be punched, are cost-effective, and have a low relative density. Examples include XPC, FR-1, FR-2, FE-3, etc., with 94V0 being a flame-retardant version.
2. Composite PCB Substrate
These boards incorporate wood pulp fiber paper or cotton pulp fiber paper as reinforcement, combined with glass fiber cloth as surface reinforcement. Both materials are bonded with flame-retardant epoxy resin. Notable examples are single-sided half-glass fiber 22F, CEM-1, and double-sided half-glass fiber board CEM-3, with CEM-1 and CEM-3 being the most common composite base copper-clad laminates.
3. Glass Fiber PCB Substrate
Sometimes epoxy boards, glass fiber boards, FR4, and fiber boards are used. Epoxy resin serves as the binder, while glass fiber cloth acts as the reinforcing material. This type of circuit board offers high working temperatures and is unaffected by environmental factors. Often utilized in double-sided PCBs, it is more expensive than composite PCB substrates, with a common thickness of 1.6 mm. Suitable for power supply boards, high-level circuit boards, and widely used in computers, peripheral equipment, and communication devices.
Three Reasons for Aging of Solder Joints in PCBA Processing
**Failure Modes of Solder Joints**
The reliability tests of PCBA processing solder joints include both reliability testing and specific analysis. The primary goal is to evaluate the reliability of integrated circuit chip electronic components and provide data parameters for the reliability design of the entire equipment. Additionally, it aims to enhance the reliability of solder joints through specific analysis of failures to find failure modes and causes. This process is crucial for improving and optimizing design processes, structural parameters, and welding techniques. Analyzing failure modes based on cycle life predictions is essential for creating mathematical analysis models. The following are three detailed failure modes.
1. **Solder Joint Failure Caused by Welding Process**
Objective conditions during welding and subsequent cleaning processes may lead to solder joint failures. SMT solder joint reliability issues primarily arise from production, installation, and usage stages. During production and installation, limitations in equipment and human errors in welding specification selection often lead to issues like false welding, solder short circuits, and other defects. In the usage stage, collisions and vibrations can cause mechanical damage, while thermal stress due to large temperature differences can lead to stress cracks. Additionally, gold and silver corrosion may occur in thick and thin film hybrid circuits due to reactions between solder materials and gold or silver-plated pins, reducing solder joint reliability. Excessive ultrasonic cleaning can also negatively impact reliability.
2. **Failure Caused by Aging**
When molten solder interacts with a clean substrate, intermetallic compounds (IMCs) form at the interface. During aging, the solder joint’s microstructure coarsens, and the IMC layer continues to grow. The failure of solder joints partly depends on the growth kinetics of the IMC layer. Although IMCs indicate good welding, excessive thickness can lead to micro-cracks or breakage in the solder joint. When the thickness surpasses a critical point, the IMCs become brittle. Due to thermal expansion mismatches between materials, solder joints experience strain during usage, potentially causing failure. Studies show that adding trace amounts of lanthanum to Sn60/Pb40 solder alloy reduces IMC thickness, doubling the thermal fatigue life and significantly improving solder joint reliability.
3. **Failure Caused by Thermal Cycling**
During usage, power supply circuit interruptions and temperature fluctuations subject solder joints to thermal cycling. The thermal expansion mismatch between packaging materials induces stress and strain in solder joints. For SMT, the coefficient of thermal expansion (CTE) of A1203 ceramic is 6 × 10^-6 °C^-1, while that of epoxy resin/glass fiber substrate is 15 × 10^-6 °C^-1. Temperature changes cause corresponding stress and strain in solder joints, generally between 1% to 20%. In THT processes, flexible pins absorb most of the strain, but in SMT, solder joints bear the strain, leading to crack initiation and eventual failure.
