Challenges on ENEPIG Finished PCBs

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Summary

Conclusions

• The wire bonding evaluation in this study indicates that a ENEPIG plated surface finish can be compatible with the standard gold ball bonding process on bare boards. However, variation in wire bondability of populated boards within and between batches makes the application of the standard gold ball bonding process or the security bump process difficult for volume production. Contamination on bonding pads during the SMT process seems to be the main factor for the variation in wire bondability of populated boards.
• The SSB process enables the gold ball bonding process on ENEPIG plated PCBs for volume production applications.

• PMLs were observed during the wire bonding process and/or wire pull test from multiple ENEPIG PCB samples.
• An overactive Ni bath resulting in compromised Ni deposit is a potential factor in PML on wire bonding pads.
• PMLs were observed with and without the evidence of hyper corrosion of Ni. PMLs due to hyper corrosion of Ni might be related to Au and Pd thickness, and/or Ni MTOs with multiple other contributing factors.
• Inclusions and hyper corrosion in the Ni layer in the wire bonding area that are at the smaller scale (approx. 5 um) could result in reliable re-wire bonding in the same pad.
• A tape test as per IPC-TM-650 is not an effective method to screen for PML on wire bonding boards.

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