In an ongoing effort to replace toxic metals used in semiconductor manufacturing, STMicroelectronics, Lexington, Mass., has developed ball-grid-array (BGA) and microBGA packages that are lead-free. These packages incorporate solder balls formed from a combination of tin, silver, and copper, rather than the traditional tin-lead alloy. The "ecoBGA" is a product of the company's ECOPACK program—launched in 1998—to develop environmentally friendly manufacturing processes ahead of any legal mandates from regulatory agencies.
The BGA package type was a likely target for such efforts. With a lead content as high as 15%, the BGA contains the most lead of any semiconductor package. More importantly, its popularity throughout the industry is steadily rising as demand grows for ICs with high pin counts.
Marketing pressures and legislation abroad are creating the impetus for electronics manufacturers to switch to lead-free processes. But much work remains before lead-free packages like the ecoBGA can go into high-volume production. STMicroelectronics has qualified its lead-free processes for production. On the customer side, however, OEMs must carry out the necessary steps—changing solder pastes and processes—to meet the new demands of a lead-free surface-mount reflow system.
Temperature is the key. Conventional solder balls contain lead and tin in a ratio of 63% to 37%, while the lead-free solder balls are 97% tin. That increase in tin content means the lead-free packages will cost about the same as conventional BGAs, despite the addition of silver and copper. Yet greater amounts of tin also raise the solder's melting point, requiring the customer to switch from industry-standard reflow temperatures of around 220°C to temperatures up to 250°C and possibly beyond.
This change will require component suppliers, board manufacturers, equipment makers, and others in the industry to requalify their products and processes for lead-free production. One issue that must be addressed is plastic packaging's tolerance of the higher temper-atures. Plastic tends to absorb water, so there is concern that the additional heat encountered in lead-free solder reflow could cause plastic components to burst from internal steam pressure.
To promote the transition to lead-free assembly, STMicroelectronics is offering samples of the lead-free BGA and microBGA, along with lead-free soldering pastes and various soldering profiles. The company also provides a daisy-chain test device in the lead-free BGA package to simplify monitoring of solder-process yield and thermal-cycle performance on board. For more information, contact Michael Hundt at (972) 466-7282.