4 Cu Wire Risks

Thermal cycling is especially prominent in LEO satellites which orbit the earth multiple times a day. TI’s Space EP products use gold bond wires instead of classic copper (Cu) bond wires typically found in commercial and automotive AEC-Q100 products in order to reduce potential risks.

As a cost savings, more and more COTS products are switching from gold (Au) bond wires to copper (Cu) bond wires. Cu bond wires are now even permitted for automotive AEC-Q100 products. On some products, either Au or Cu bond wire could be used with the decision on which wire used is at the discretion of the supplier, but is usually based on available Cu wire bonding capacity. Many times, the customer does not know which bond wire material is used on any given lot.

While there has been continuous improvement in the Cu bonding process and Cu bond wire reliability, there are still potential risks, especially in harsh environment applications. Cu wire bonding requires much tighter process controls or bond integrity and reliability issues could result. Sporadic Cu wire corrosion has occurred from interaction with the plastic mold compound. There have been some cases where there has been corrosion at the Cu bond wire/lead frame interface when there has been package delamination. Perhaps of most concern for harsh environments is that Cu wire has a higher temperature coefficient than Au, making it more susceptible to bond neck breaks during thermal cycling. This could be critical in some LEO applications where a satellite might go through temperature cycle extremes several times per day.