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During functional test of control module boards used in a multiple sub-array of a testable antenna, two boards failed. The root cause for the failures was identified as "unable to write specific addresses at system speeds." When diagnosing the issue, it was narrowed down to an SRAM that was supplied by an electronics part broker. The parts in question were procured from the broker, an approved diminishing material supply (DMS) supplier, due to unavailability from a franchised distributor of the original components manufacturer (OCM). When reviewed by the internal Failure Review Board, it was determined that a comparison of SRAM parts supplied by the broker should be compared with parts from the distributor to determine if there were any observable differences in the parts.
Figure 1: Comparison of two SRAM parts with different lot numbers.
Analysis Approaches and Techniques
A total of seven different methods which ranged from nondestructive to destructive were used to make a determination about the SRAM parts being suspect counterfeit. Any individual analysis does not make a clear case on its own merits. However, to make a legal case for suspect counterfeit, enough due diligence is necessary.
The following outlines the seven analyses used to make the case:
1. Visual inspection by optical microscopy
2. X-ray
3. De-capsulation
4. Scanning acoustic microscopy
5. FTIR
6. Electrical test
7. Discussions with OCM
Visual Inspection by Optical Microscopy
Once the failure occurs on a component or subsystem, typically there is an optical inspection to determine if there was any physical damage to the part either before or during testing. Damage can occur from a variety of sources including handling, testing conditions and setup, foreign object damage or debris (FOD), fixturing, etc. Figure 1 shows a comparison of an SRAM received by an authorized distributor and the broker in question. It was noted that the lot number of the broker part was not in the OCM database.
Figure 2: Lead and mold inspection. Different mold interface and pin width.
In and of itself, this does not constitute a smoking gun, but it does inspire one to continue the investigation. Upon further visual inspection, it appeared the workmanship, or quality of the part around the leads suggested a difference in mold processing (Figure 2). Because visual inspection is subjective and directed by any given customer requirements, incoming inspection (5-10X at AQL) easily can miss the inconsistencies. This is especially true when suspect counterfeit parts are mixed in the same delivery packaging and 100% inspection is not performed.
Finally, there was a measurement of pin width between the two different leads. The leads from the distributor parts were on the order of 14.5 mils wide, whereas the lead width from the broker parts was 12 mils. The difference led to the next step in the investigation, namely X-ray.
To read this entire article, which appeared in the July 2017 issue of SMT Magazine, click here.
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