Practical Guidelines for Improving PCB Reliability

High reliability PCB performance is not only determined by testing after production.

In our experience, long-term reliability is strongly influenced by material selection, stack-up design, manufacturing complexity, and process stability.

Based on more than 25 years of PCB manufacturing experience, we recommend the following considerations:

High Reliability PCB

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1. Select the Right PCB Material — MTG Is Often the Best Balance

For high reliability applications, material selection is one of the most important factors.

Standard Tg materials are cost-effective, but to achieve lower cost, some materials may contain a higher percentage of inorganic fillers.

Excessive filler content can:

• Increase PCB brittleness
• Reduce resin flow during lamination
• Affect resin filling between glass fabrics
• Increase the risk of interconnection defects (ICD)

High Tg materials provide excellent thermal performance but usually come with higher costs.

In many automotive PCB applications, Mid Tg (MTG) materials are widely selected because they provide a good balance between reliability and cost performance.

The best material choice depends on:

• Operating temperature
• Thermal cycling requirements
• Product lifetime
• Cost target

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2. Avoid Excessive Board Thickness When Possible

A thicker PCB is not always more reliable.

When impedance requirements and mechanical requirements allow, thinner boards are often preferred.

For many applications:

1.6mm or below is a practical and stable choice.

Excessive thickness can increase:

• Thermal stress
• Lamination difficulty
• Manufacturing complexity

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3. Keep Layer Count as Simple as Possible

More layers do not always mean better reliability.

When the design allows:

• Single-sided PCB
• Double-sided PCB
• 4-layer PCB

are usually easier to manufacture and control.

As layer count increases:

• More lamination cycles are required
• Manufacturing variables increase
• Process control becomes more challenging

For high-volume production, even a small process variation can create reliability risks.

A simpler PCB structure is often a more stable PCB structure.

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4. Choose Surface Finish According to Application Requirements

Surface finish selection should match the component requirements.

HASL

Recommended when:

• No fine-pitch components
• No small pads
• Standard SMT requirements

HASL is a mature and stable surface finish.

ENIG

Recommended when:

• Fine-pitch components are used
• BGA/QFN packages are required
• Flat surface requirements exist

For ENIG applications, we recommend specifying:

2µ" minimum gold thickness

Both HASL and ENIG are widely proven and reliable surface finishes when properly controlled.

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5. Maintain Sufficient Pad Spacing to Reduce ICD Risk

PCB design directly affects manufacturing reliability.

When possible:

Keep pad-to-pad spacing above 0.4mm.

Insufficient spacing can increase:

• Resin starvation risk
• Lamination challenges
• Interconnection defect (ICD) possibility

Good PCB reliability starts from good PCB design.

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6. Avoid HDI Unless It Is Really Necessary

HDI technology provides excellent routing capability.

However, laser microvias introduce additional manufacturing challenges compared with traditional through holes.

When a conventional through-hole structure can meet the electrical requirements:

A simpler through-hole design is often preferred for long-term reliability.

HDI should be selected when required by:

• Component density
• Miniaturization
• Signal integrity requirements

Not simply because it is a more advanced technology.

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7. Ensure Sufficient Plated Through Hole Copper Thickness

Via reliability depends strongly on copper thickness inside the hole wall.

While IPC Class 2 requirements define minimum acceptance criteria, increasing hole copper thickness can significantly improve reliability margin.

For high reliability applications, we recommend:

Hole copper thickness ≥25µm

Thicker copper plating reduces the risk of:

• Thermal cycling cracks
• Barrel cracks
• Via fatigue failures

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Conclusion

High reliability PCB manufacturing is not achieved by one single process.

It comes from the combination of:

• Proper material selection
• Reliable stack-up design
• Controlled manufacturing processes
• Appropriate surface finish
• Reasonable complexity

In many cases, a simpler and well-controlled PCB structure can provide better long-term reliability than an unnecessarily complex design.