Masters Abstracts (1995)
DHANESHWAR, KAMALESH
(March, 1995), TRW Automotive Elec. Group, Marshall, IL
Email: dhanesk@shsmtp.fh.trw.com
The Intrinsic Measurement of Solderability Using Wetting Balance Analysis
Solder joints in a surface mount printed wiring board (PWB) assembly provide electrical connections and mechanical support. Solderability is an important factor in determining the integrity of a solder joint. Therefore, the importance of the solder joint dictates the need for good solderability of the soldering surfaces and wetting characteristics of solder pastes in surface mount PWB assembly. Besides, the problems associated with the repair and inspection of solder joints enhances the need to ensure good solderability. Knowledge about the solderability of surface mount components and boards and the exact behavior of solder pastes during soldering can be very useful while assembling PWBs. This can help prevent the enormous costs associated with the repair or rejection of defective circuits. The wetting balance is a versatile apparatus used to quantitatively measure the solderability of specimens.
In this research a microprocessor controlled closed loop temperature controller was used to subject the solder paste to a heating cycle similar to the temperature profile inside a reflow oven. A small deposit of solder paste was used to produce wetting in contrast to the original test procedure in which the test specimen is dipped in a flux prior to immersion into the molten solder bath (maintained at a constant temperature). Standard test parameters that are to be used during the evaluation of solderability with respect to the characteristics of the solder deposit such as the area, thickness, shape and the immersion depth of the test specimen have been identified through experiments designed using Taguchi methods.
A comprehensive study was conducted on several commercially available solder pastes (water soluble and no clean) for the wetting characteristics during reflow using this new test procedure. This research provides the surface mount process engineer with an excellent tool to understand the capabilities of the components and the solder pastes prior to using them in actual PWB assembly lines.
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