Temperature cycling and temperature shock are particularly
suitable environmental stresses with which to evaluate or stress screen
electronic assemblies. These environments cause expansion and contraction of
the various materials, and where differences in thermal coefficients of
expansion exist, failures may occur. In the case of LCCs on MIBs, these
environments may cause open solder joints, open vias, or open conductor lines.
Temperature shock is usually conducted by
cycling the unit over thetemperature range of-55°C to +85°C or from -65°C to + 125°C depending
on the size of the test item and its intended end use environment. The test
item is transferred directly from one chamber to the other. Temperature
cycling is usually performed to the same temperature ranges; however, the
transition rate is controlled. The normal methods employed to detect failures
are a continuity test at the board level and a visual inspection plus
functional test for the completed assembly.
Various quantities of ceramic modules have been subjected up to
1000 temperature cycles and/or temperature shocks with little or no
detrimental effects. The most predominant observation was minor solder joint
surface cracks found by visual inspection after completion of the test.
Although countless numbers of the baseline
polymer-glass MLBs have been temperature-cycled, little data exists on the effects
of subjecting these MLBs to long term cycling, i.e., 100 to 500 cycles. One
such experiment was obtained from the publication "Environmental Stress
Screening Guidelines for Assemblies" (see Appendix B) wherein 15 polymer-glass MLBs
were subjected to temperature shockfrom -50°C to +100°C for 300 cycles. This test produced
two solder joint failures and several component failures. It was concluded
that 50 cycles of temperature shock could be safely applied to the MLBs
without decreasing useful life.
In nearly all cases, failures identified during temperature
cycling or temperature shock were attributed to either variations in raw
materials or in manufacturing processes. The test data and technical articles
reviewed leave no doubt that consistent raw materials and a stable
manufacturing process are essential to producing a reliable ceramic