I. OBJECTIVE:
Lead containing solders, particularly tin-lead solders, have been widely used as low temperature
joining alloys for some time because of their good combination of process attributes, properties
and cost. However concerns about lead toxicity have resulted in banning of lead-containing
solder for use in potable water piping, food and beverage cans, and automobile bodies. In the
electronics industry, the main concern regarding lead-containing solders arises from ultimate
disposal of solder-containing devices in landfills when recycling of electronic components is not
properly practiced.
There are many candidate alloys being considered as replacements for lead-containing solders,
however none has yet emerged as a “drop-in” replacement. Of these, the Sn-9% Zn eutectic
alloy, possibly with other small additions to improve attributes, appears promising, as reviewed
below. There have already been a number of investigations on this alloy composition which
show its advantages, however concerns remain with regard to durability over time of both the
soldered joints made with this alloy and solder pastes containing Sn-Zn alloy.
The objective of this particular program is to study fatigue properties of the Sn-9% Zn eutectic
alloy at an elevated temperature typical of electronic circuit service (85°C) under both dry and
moist conditions and also under conditions of thermomechanical cycling that simulate on/off
circuit behavior. The data provided by this program will be important in addressing concerns by
electronic companies with regard to potential degradation of this solder alloy by means of zinc
oxidation. We are optimistic that such degradation will not be a problem because zinc oxide will
likely form on the external solder surface and likely prevent or greatly slow down the rate of
oxidation. However data are needed concerning long-term electrical and mechanical properties
to prove this.
II. ECONOMIC INCENTIVE:
About 100,000 tons of solder are used annually with 60%, or 60,000 tons going to electronics.
40% of this, or 24,000 tons is used in North America, an equal amount in Japan and Southeast
Asia and much of the rest in Western Europe. The Sn-Zn eutectic is a 91% Sn-9% Zn. Thus, if
an equal weight of the current solder market is converted to the Sn-Zn alloy, then the 60% going
to electronics would consume 5400 tons annually. At a price of $1,000/ton for special high
grade zinc, this would give a market of $5.4 million. However solder alloys are typically sold.....
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