Page 58
www.us-
tech.com Materials Testing for Microelectronics Continued from page 56
uses a small heated pin to make a sol- der joint between the part being pulled and the force measurement system. Pin geometries can be very small and
Impact Failure Modes Quite often impact produces
failure modes not observed in routine low strain rate tests. At high strain rates, solders yield at sig- nificantly higher stres ses and as a result other parts of the bond become more highly loaded and can fail first. High-speed testing is widely used for assessing the brittleness of solder joints or the sus- ceptibility of a PC board to pad cratering under impact conditions (JESD22-B115A, JESD22-B117A).
Connector Testing Connector failures
Weibull plot for number of cycles to failure at a bend angle of 80°.
with care, a bond can be made to fea- tures that are <100µ in diameter. One application is pad cratering (IPC
are generally associated with abrasion of the con- tact materials. Re peated insertion and retraction of connectors wears away
coatings and can lead to corrosion of the base metal. Ongoing wear, in general, has a detrimental effect on
Creep Measurements Creep measurements
are important for solders, polymers and adhesives where large strains can develop over time, and strain rates are very tem- perature-sensitive. Although creep is es -
sentially a shearing pro cess, it can be assessed using ten- sile, compressive and bend tests.
There are three types Materials testing table.
9708). Latent damage introduced dur- ing processing of the PC board can cause a pad to fail by crack propaga- tion through the composite.
the insertion force and electrical resistance of the connections. Cyclic loading of connectors not only pro- vides useful information for deter-
of creep test: The stress rup- ture test, measures the long term load bearing charac- teristics of the component. Stress or load relaxation methods, measure the slow replace- ment of elastic strain by plastic strain at constant total strain. The
melting point. The behavior of plas- tics depends on their glass transition
Creep for leaded solder. Continued on next page
mining the number of times connec- tors can be plugged and unplugged, but is also a means of testing design
constant stress/load test measures sample strain rate under conditions of constant load or stress.
February, 2013
Peel test.
changes, such as pin shape, spring force and coatings.
As a rule of thumb, for metals,
creep is important for temperatures above half the materials’ absolute
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