Low Temperature Solder Attach of SnAgCu Bumped Components for a Flexible Hybrid Electronics Based Medical Monitor

The use of commercial electronics components with Tin-Silver-Copper solder bumps normally calls for relatively high cost substrates, posing a challenge for disposable (inexpensive) products. The present effort addresses the feasibility of reducing reflow temperatures through the use of a eutectic Tin-Bismuth solder paste for products that do not have to survive significant thermal cycling. A set of experiments was conducted to assess the effects of paste volume and reflow profiles on solder joint strength and low cycle fatigue resistance. Both strength and fatigue resistance tended to decrease with decreasing peak temperature and paste volume, but indications are that performances comparable to those of conventionally reflowed Tin-Silver-Copper solder joints can be achieved even with laser reflow and a peak temperature as low as 160C. This offers promise for the use of low cost substrates such as PET.