Wetting, solder temperature control

The adhesion of specimens subjected to environmental exposure tests was evaluated prior to and subsequent to the contact. Wet thermal shock testing consisted of five cycles each for IS minutes in boiling water and 2 minutes in ice water. The maximum transfer time between the two baths was 30 seconds. Thermal and temperature/humidity exposures were performed in controlled atmosphere chambers for 200 hours. Simulated solder tests comprised immersing the test. specimen in a silicone oil followed by solder flotation. The solder temperature varied from 232 to 288 C and the contact time was S or 10 seconds. In some cases, two flotations were performed on the same sample. The effect of a heat treatment at 135 C prior to solder testing was examined the heat treatment time varied from 0 to 16 hours. ... 

The chapter authors feel that the sessile drop technique represents a more precise and versatile tool for quantifying wetting, particularly in high-temperature systems where environmental control is imperative. For solderability assessment, the technique involves placing a solder alloy on a preheated substrate either as a molten (Uquid) drop or as a solid mass that subsequently melts. Wetting in the sessile drop method is spontaneous rather than forced. Therefore, it shares a strong similarity with the conditions that prevail in many commercial soldering processes. 

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