SMTA International Conference Proceedings


OPTIMIZING CLEANING ENERGY IN ELECTRONIC ASSEMBLY SPRAY IN AIR SYSTEMS: PHASE II

Authors: Steve Stach and Mike Bixenman
Company: Austin American Tech and Kyzen
Date Published: 9/25/2005   Conference: SMTA International


Abstract: At the SMTA 2004 tech forum, Stach & Bixenman (2004) presented research for optimizing cleaning energy in batch and inline cleaning systems. The research questions for the 2004 study asked: What equations define surface energy at board level? How does this energy affect the fluid delivery design in a cleaning system? How much impingement pressure is needed at the board level? Which is better, high pressure or high flow?

Defining an optimized electronic assembly cleaning system requires an understanding of the balance between the static (potential) and dynamic (kinetic) energies to achieve maximized cleaning performance. Attributes or characteristics that influence cleaning performance center around surface energy, surface tension, capillary action, spray nozzle design, equipment design, time, temperature, and cleaning chemistry.

Phase II of this research test the process cleaning rate equation, which equals the static cleaning rate (chemical forces) plus the dynamic cleaning rate (mechanical forces) using spray-in-air cleaning equipment. The baseline for this experiment establishes the solubility rate of the cleaning solution, at static conditions, to determine the dissolution rate of flux residue, at a pre-determined cleaning chemistry concentration and temperature.

Once the cleaning rate is known, how will it be improved by applying physical energy to the board surface? The designed experiment will test the effect of energy applied to the board surface by varying pressure at the board surface. The study’s hypothesis infers that a known dissolution rate and a known surface energy configuration allows an equation to calculate cleaning time and distance. The response variables will be video imaging of the actual cleaning tests, and removal efficiency using ultraviolet detection of residue under low standoff test vehicles.

Independent variables consist of substrate standoff heights, cleaning temperature, and cleaning time with various attributes. Constants include fixed amount of nozzles per square inch, predetermine maximum force that does not result in component marking damage, and chemistry concentration.

Key words: Process Cleaning Rate, Cleaning, Pb-free



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