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www.us-tech.com
June, 2017
Developing Low-Temperature Solder for Sensitive Components
By Steven Teliszewski, Technical Manager, Interflux Electronics T
he high temperatures used in today’s lead-free soldering processes can do damage to
sensitive components and even to PCB substrate materials. Nearly every electronic device has some crit- ical components built into it. These include such components as capaci- tors, BGAs, fuses, displays, crystal oscillators, LEDs, and many others that have relatively low temperature limits. Thermal stress damage can be detected in most cases by visual observation, or by optical, X-ray, in- circuit, or functional testing.
Low melting point solder alloys have traditionally been mechanically weak. Interflux looks to change that with its LMPA-Q.
It is a lesser-known fact that
these high soldering temperatures can also cause a slight shift in the properties of some components. This will have an impact on the function- ality of the finished device, which is a serious concern for sensitive equip- ment, such as measuring instru- ments. These kinds of failures are often much harder to determine. One way to solve the problems
that result from high soldering tem- peratures is to use a solder alloy that
Megger’s handheld measurement devices must withstand harsh shock and vibration.
specifically to overcome these limita- tions. The solder alloy was tested for its suitability in production on a handheld, high-accuracy measuring device from U.K.-based Megger Instruments. At the time of the test,
SMT and through-hole components. Its sensitivity to temperature comes mainly from the various capacitors that are all strongly affected by heat. The boards were printed with Interflux’s DP 5600 LMPA-Q solder
has a lower melting point. Currently, these alloys have
limitations in mechanical strength, but they allow for much lower solder- ing temperatures. Shock and vibra- tion resistance tend to be their weak- est characteristics, limiting the field of use for these alloys. Interflux has developed its LMPA™-Q low melting point alloy
the device was being soldered with an SnAg3Cu0,5 (SAC 305) alloy, was sensitive to the heat in the soldering process, yet needed to be shock- resistant in the field.
Soldering Sensitive Components The Megger measurement de -
vice contains a double-sided, immer- sion-silver finished PCB with both
paste with ROL0 classification. The units were then reflow-soldered in a full convection oven without nitro- gen. The profile’s peak temperature was below 205°C (401°F) in order to accommodate the sensitive compo- nents. The through-hole compo- nents were soldered with LMPA-Q solder wire. Handheld devices must have
excellent shock resistance in the field. This is to protect against the usual wear and tear of daily use and to safe- guard against accidents, such as dropped equipment. This particular property has traditionally been the weak point of low melting point solder alloys. This presented an opportunity to test Interflux’s LMPA-Q. The Megger measurement de -
vice was submitted to vibration and shock resistance testing according to BS EN 60945 and BS EN 60068. To ensure objective results, the tests were performed by a third-party spe- cialized testing lab.
Shock and Vibration Testing A half-sine shock test per-
formed shocks in both directions of all three axes. Shocks lasted 11 ms, with a peak acceleration of 30g (g- force), or were defined by the practi- cal limitations of the test setup. In this case, the shock in the x-axis was limited to 10g, due to the breaking off
Continued on next page
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