Abstract

Dross generation has always been a costly issue for the electronics assembly industry. At least half, and, in many cases, more than half of the metal (solder) purchased for electronic manufacture is wasted as it becomes tied up in dross. With the advent of lead-free solders, as well as the spike in tin prices, the moderate economic pain of dross generation has become acute. In addition to metal cost, lead-free solders have become known to exacerbate quality issues, such as copper dissolution. A process introduced two years ago cures virtually all problems caused by dross and has now been shown in production to mitigate some of the other issues associated with lead-free solders.

This paper will show the true cost of dross, including metal replacement, loss of efficiency and safety, as well as environmental and quality issues which clearly demonstrate a need for a solution to this problem. In addition to dross elimination, the process has been shown in the lab to reduce temperatures for wave and selective soldering and to improve wetting. Updated full production data at major EMS assemblers, as well as lab test data, will be presented.

In addition to answering the technical questions, the "why" and "how" of the economics of dross will be examined and a specific and significant cost savings scenario will be presented based on the first two years of full production.

This is a new paper which builds on one presented previously at IPC APEX Expo. This paper contains new information with the economic and quality examples based on full production data at major companies.

Economic and Technical Advantages of Chemical Dross Elimination and Prevention

Solder dross has been a problem for the electronic assembly industry since wave soldering overtook manual placement and soldering decades ago. Dross is a costly by-product of molten solder, oxygen and turbulence. Once solder is converted into dross it becomes hazardous waste--with an emphasis on "waste." When solder cost was under $2.50/lb, sending out 50 to 70% of your solder and getting a fraction of its value was not a big deal. With all metal prices hitting new all-time highs, and with the mandated use of very expensive lead-free solders, the cost of dross has now gotten the attention of upper management at most leading companies.

Consider this: An average wave solder machine generates 2.7 pounds of dross per hour. Dross causes solder related defects, higher lead-free alloy melting points cause even more dross, dross creates defects, such as bridging, shorts and skips, and you also have to consider the cost to remove the dross, clean the unit and then add solder and, perhaps, even recalibrate the wave. Overall, dross is a very expensive and disruptive process.