Techniques for Analyzing Printed Circuit Board Assemblies (PCBAs)
Failure analysis of PCBAs will depend on the nature of the failure symptoms. However, the general approach is as follows,
• Review all available documentation
• Examine the assembly under a stereomicroscope and document any anomalies (e.g. suspect solder joints, mechanical damage, discoloration, suspected contamination or corrosion, etc.)
• Electrically isolate and/or verify the failure
• PWB related failures generally require cross-section preparation to reveal the failure site and root cause
• Component related failures require either decapsulation or cross-section preparation to reveal the failure site and root cause
• Contamination and corrosion related failures often can be characterized without sectioning or decapsulation
• SEM/EDS examination is performed to document the failure site and resolve root cause. High resolution images are used to identify the failure mechanism and elemental analysis can reveal chemical or material related factors
• Generate a compressive report including all relevant background information, analysis results, and conclusions
Failure analysis of PCBAs can be made more timely and cost effective through awareness of some “dos and don’ts”:
- Provide all available background information including previous test failures, touch-up operations, replaced components, failure symptoms, environmental variables, and failure history of other related PCBAs.
- Provide documentation including assembly drawing, electrical schematic, PCB drawing, and parts list.
- Carefully handle the PCBA to avoid introducing damage or contamination that might obscure the failure cause.
- Don’t reflow solder joints on suspect components. This will mask solder joint failures and potentially damage the PCB.
- Don’t use mechanical or electrical probe pressure to attempt to heal electrically open solder joints or PCB vias, as this will obscure the root cause of the open circuit condition.
The following paper discusses these concepts as well as failure mechanisms found in PCBAs: