10 Characteristics of High Reliability PCBs

Many PCB manufacturers have huge competition with each other nowadays so parts suppliers insist on costs down under strong survival pressure. The situation could lead to a bad result, that is some suppliers tilt to purchase more cheap materials to replace good quality materials. Cheap means bad quality and lower cost, but hidden huge hazards at the same time. On other hand, bad PCB will shorten the service life of the product.

Short life is a manifestation of poor PCB reliability, On the contrary, high reliability.

What is high reliability？

As known, electronic products have its life expire. So, someone definition high reliability: products permission several fault and be acceptable under the specified conditions and at the specified time.

It has normal common definition: people reckon it’s high reliability that is when products beyond life expire be repaired and then used a period.

Origin:

“Reliability” was originally proposed specifically for electronic tubes, and was mainly based on military research. American defense establish famous electronics facility reliability group(AGREE,Advisory,Group on Reliability of Electronic Equipment) at August 1952.

The group submitted a report and suggest reliability testing at manufacturing electronics facility. And then many company quality department and enterprise administrator began to establish specifically department, operation reliability testing.

After then, as electronics technical develop, customer have more and more strict demand to product, espicially, some big brand, and other hand, small manufaturing follow the trend for purse the high quality. To high reliability, the trend in the future will be purse higher quality and cost down at the same time.

As a core assembly of electronics, PCB delegate the industry develop level at now. Any product should be emphasized high reliability, step further speaks, PCB supplier should guarantee high reliability.

Hight reliability pcb have 10 feature:

1. hole wall copper thick is more than or equal 20μm.

Выгода: Strengthen reliability, include renovated capacity of resistance swell on Z axis.

Risk of not doing so: when blowing hole, eliminate gas, or assembly process, could lead to electrical connectivity issues, or may fail under load conditions during actual use.

2. No soldering repair or open circuit repair.

Выгода: perfect circuit can ensure reliability and safety, no maintain, no risk.

Risk of not doing so: If not repaired properly, it will cause the circuit board to open circuit. Even if repaired ‘properly’, there is a risk of failure under load conditions (vibration, и т. д.) that may fail in actual use.

3. Use international well-known plates, do not use inferior brands.

Benefits: Improved reliability, longevity, and known performance.

Risk of not doing so: The use of inferior quality boards will greatly shorten the life of the product. В то же время, the poor mechanical properties of the board mean that the circuit board cannot perform the expected performance under the assembled conditions. Impaired characteristics can result in poor impedance performance.

4. Use high-quality ink

Benefits: Ensure the quality of circuit board printing, improve the fidelity of image reproduction, and protect the circuit.

Risk of not doing so: Poor quality inks can cause adhesion, flux resistance and hardness problems. All of these issues can cause the solder mask to detach from the board and eventually lead to corrosion of the copper circuit. Poor insulation properties can cause short circuits due to accidental electrical continuity/arcing.

5. Exceed the cleanliness requirements of IPC specifications

Benefits: Improved PCB cleanliness improves reliability.

Risk of not doing so: Residues, solder build-up on the board pose a risk to the solder mask, ionic residues can cause corrosion and contamination of the solder surface, which can lead to reliability issues (bad solder joints/electrical failures) and ultimately increase the occurrence of actual failures probability.

6. Strictly control the service life of each surface treatment

Benefits: Solderability, надежность, and reduced risk of moisture intrusion.

Risk of not doing so: Solderability problems may occur due to metallographic changes in the surface treatment of older boards, while moisture intrusion may cause delamination, inner layer and hole wall separation (open circuit) problems during assembly and/or actual use . Taking the surface tin spraying process as an example, the thickness of tin spraying is ≧1.5μm, and the service life is longer.

7. High quality block hole

Benefits: high quality block hole will reduce fault on assembly.

Risk of not doing so: Chemical residues from the gold immersion process may remain in holes that are not fully plugged, causing problems such as solderability. Кроме того, there may be tin beads hidden in the holes. During assembly or actual use, the tin beads may splash out and cause a short circuit.

8. The tolerance of CCL meets the requirements of IPC 4101 ClassB/L

Выгода: Tight control of dielectric layer thickness reduces deviation from expected electrical performance.

Risk of not doing so: The electrical performance may not meet the specified requirements, and the output/performance of the same batch of components may vary greatly.

9. Strictly control the tolerances of shapes, holes and other mechanical features

Выгода: Tightly controlled tolerances improve product dimensional quality – improved fit, form and function.

Risk of not doing so: Problems during assembly, such as alignment/mating (problems with press-fit pins are only discovered when assembly is complete). Кроме того, the mounting into the base can be problematic due to increased dimensional deviations. According to the high reliability standard, the hole position tolerance is less than or equal to 0.075mm, the hole diameter tolerance is PTH±0.075mm, and the shape tolerance is ±0.13mm.

10. The thickness of the solder mask is thick enough

Benefits: Improved electrical insulation properties, reduced risk of peeling or loss of adhesion, increased resistance to mechanical shock – wherever it occurs!

Risk of not doing so: Thin solder mask can lead to adhesion, flux resistance and hardness problems. All of these issues can cause the solder mask to detach from the board and eventually lead to corrosion of the copper circuit. Poor insulation properties due to thin solder mask, can cause short circuits due to accidental conduction/arcing.