Issues in the replacement of lead-bearing solders

Abstract

The use of soft solders, particularly those containing lead, dates back nearly 5,000 years. Solders similar to the materials used to seal the aqueducts of ancient Rome are now an important building block in the manufacture of high-speed computer assemblies. This history attests to the technological versatility of soft solders and, in particular, the solder alloys that contain lead. However, the health effects of prolonged exposure to lead have also been documented; measures to limit human exposure-at the work place and indirectly through the environment-are being considered. The successful introduction of lead-free solders into future electronic products will rely heavily upon their solderability, which can be evaluated by test procedures such as the meniscometerjwetting balance technique and the capillary flow test.

A review of photovoltaic module technologies for increased performance in tropical climate

“…At elevated temperature, the differential material expansion mismatch induces thermal stresses on the interconnection which culminates in fatigue loading occasioned by the environmental temperature cycle history. Consequently, the interconnection surfers delamination, crack initiation, propagation and rupture [126], [137]- [142]. Interconnection degradation has been reported by [117][143], [144] as causing over 40% of PV failures and this figure is greater in the tropical climate.…”

Development of a new Pb-free solder: Sn-Ag-Cu

“…Wettability is defined as the tendency for a liquid metal to spread on a solid surface (2). This is a precursor to an important property of any solder: solderability.…”

“…When comparing the performance of different solders or fluxes the contact angle provides the best indicator for the performance of the material in question (2). Some wettability parameters for two solders, Sn-37Pb and Sn-3.5Ag (both eutectic compositions in wt%) at 260 "C are given in Wetting is promoted by small values of y s~ and XF in combination with a relatively large value of YSF.…”

“…The liquidus curve on each isopleth is easily seen on solute poor samples (to the left of the proposed ternary eutectic composition (see Figure 5. 2) . To the right of the eutectic composition the liquidus curve a trend is difficult to identify.…”

“…Solders have been used for nearly 4000 years. The earliest recorded solder use dates back to the Egypt around 3600 BC (2). Sn-Pb solders have been used for joining since before Roman times.…”