Highly reliable PCB
1. What is reliability pcb?
Reliability refers to "trustworthy" and "trustworthy", which refers to the ability of a product to complete a specified function under specified conditions and within a specified time. For end products, the higher the reliability, the higher the guarantee for use.
PCB Manufacture reliability refers to the ability of the "bare board" to meet the production conditions of subsequent PCBA assembly, and to maintain normal operation functions for a certain period of time under a specific working environment and operating conditions.
2. Why should we pay attention to reliability
In 1986, the US space shuttle "Challenger" exploded 76 seconds after takeoff, killing 7 astronauts and losing 1.3 billion U.S. dollars. The root cause of the accident was a failure of a sealing ring!
In the 1990s, the United States UL issued a document saying that PCBs produced in China caused many equipment and instruments to catch fire in the United States. The reason was that China's PCB factories used non-flame retardant plates, but were marked with the UL mark.
Whether in the manufacturing assembly process or in actual use, PCB must have reliable performance, which is very important. In addition to related costs, defects in the assembly process may be brought into the final product by the PCB, and malfunctions may occur during actual use, leading to claims. Therefore, it is no exaggeration to say that the cost of a high-quality PCB is negligible.
In all market segments, especially those that produce products in key application areas, the consequences of such failures are disastrous.
These aspects should be kept in mind when comparing PCB prices. Although the initial cost of reliable, guaranteed, and long-life products is high, they are still worth the money in the long run.
Three, the 14 most important features of high-reliability circuit boards
1. 25 micron hole wall copper thickness
Benefits: Enhance reliability, including improving the expansion resistance of the z-axis.
Risks of not doing so: blow holes or outgassing, electrical connectivity problems during assembly (inner layer separation, hole wall breakage), or failure under load conditions in actual use. IPCClass2 (the standard adopted by most factories) requires 20% less copper plating.
2. No welding repair or open circuit repair
Benefits: perfect circuit can ensure reliability and safety, no maintenance, no risk
The risk of not doing this: If the repair is not done properly, it will cause the circuit board to open. Even if the repair is ‘proper’, there is a risk of failure under load conditions (vibration, etc.), which may cause failure in actual use.
3. Exceeding the cleanliness requirements of IPC specifications
Benefit: Improving PCB cleanliness can increase reliability.
The risk of not doing so: Residues and solder accumulation on the circuit board bring risks to the solder mask. Ionic residues can cause corrosion and contamination risks on the soldering surface, which may lead to reliability problems (bad solder joints/electrical failures), and Eventually increase the probability of actual failure.
4. Strictly control the service life of each surface treatment
Benefits: solderability, reliability, and reduce the risk of moisture intrusion
The risk of not doing this: due to the metallographic changes in the surface treatment of the old circuit boards, soldering problems may occur, and moisture intrusion may cause delamination, inner layers and hole walls during the assembly process and/or actual use Separation (open circuit) and other issues.
5. Use internationally well-known substrates-do not use "local" or unknown brands
Benefit: Improved reliability and known performance
The risk of not doing so: Poor mechanical performance means that the circuit board cannot perform the expected performance under assembly conditions, for example: high expansion performance will cause delamination, disconnection and warpage problems. Weakened electrical characteristics can lead to poor impedance performance.
6. The tolerance of the copper clad laminate meets the requirements of IPC4101ClassB/L
Benefits: Strictly controlling the thickness of the dielectric layer can reduce the deviation of expected electrical performance.
The risk of not doing this: the electrical performance may not meet the specified requirements, and there will be large differences in output/performance of the same batch of components.
7. Define solder mask materials to ensure compliance with IPC-SM-840ClassT requirements
Benefits: NCAB Group recognizes "excellent" inks, realizes ink safety, and ensures that solder mask inks meet UL standards.
The risk of not doing so: Inferior ink can cause adhesion, flux resistance and hardness problems. All these problems will cause the solder mask to separate from the circuit board and eventually lead to corrosion of the copper circuit. Poor insulation properties can cause short circuits due to accidental electrical continuity/arc.
8. Defining the tolerances of shapes, holes and other mechanical features
Benefits: Strict control of tolerances can improve the dimensional quality of products-improve fit, shape and function
The risk of not doing this: problems in the assembly process, such as alignment/fitting (only when the assembly is completed will the press-fit needle problem be found). In addition, due to the increased size deviation, there will be problems when installing the base.
9. NCAB specifies the thickness of the solder mask, although IPC does not have relevant regulations
Benefits: Improve the electrical insulation properties, reduce the risk of peeling or loss of adhesion, and strengthen the ability to resist mechanical impact-no matter where the mechanical impact occurs!
The risk of not doing this: thin solder mask can cause adhesion, flux resistance and hardness problems. All these problems will cause the solder mask to separate from the circuit board and eventually lead to corrosion of the copper circuit. Poor insulation properties due to the thin solder mask layer can cause short circuits due to accidental conduction/arc.
10. Appearance requirements and repair requirements are defined, although IPC does not define
Benefits: Careful care and carefulness in the manufacturing process create safety.
The risk of not doing this: multiple scratches, minor injuries, repairs and repairs-the circuit board works but doesn't look good. In addition to the problems that can be seen on the surface, what are the invisible risks, the impact on assembly, and the risks in actual use?
11. Requirements for the depth of the plug hole
Benefits: High-quality plug holes will reduce the risk of failure during assembly.
The risk of not doing so: The chemical residue in the gold deposit process can remain in the hole that is not full of the plug hole, which will cause problems such as solderability. Moreover, there may be tin beads hidden in the holes, and the tin beads may splash out during assembly or actual use, causing short circuits.
12. PetersSD2955 specifies the brand and model of peelable blue glue
Benefits: The designation of peelable blue glue can avoid the use of "local" or cheap brands.
Risk of not doing so: Inferior or cheap peelable glue may blisters, melt, crack or solidify like concrete during the assembly process, so that the peelable glue cannot be peeled off/doesn't work.
13. NCAB implements specific approval and ordering procedures for each purchase order
Benefits: The implementation of this program can ensure that all specifications have been confirmed.
The risk of not doing this: If the product specifications are not carefully confirmed, the resulting deviation may not be discovered until the assembly or the final product, and it will be too late at this time.
14. Do not accept boards with scrapped units
Benefits: Not using partial pcb assembly prototype can help customers improve efficiency.The risk of not doing this: all defective boards require special assembly procedures. If the scrap unit board (x-out) is not clearly marked, or if it is not isolated from the board, it is possible to assemble this board. Known bad board, thus wasting parts and time .