By Les Hymes (auth.), Les Hymes P.E. (eds.)
The impetus to create this booklet originated from numerous issues. this type of used to be the perceived worth to the of a set in a single quantity of a variety of info pertinent to the explanations and strategies for de fluxing revealed wiring assemblies (PWAs). This ebook is predicted to be of use not just to these engaged within the electronics packaging but in addition to these in comparable fields looking details touching on workable equipment of facing one of many en vironmental problems with our time: the destruction of the ozone layer surrounding and maintaining the planet with which we've been entrusted. the amount of data relative to supplying PW As freed from residues advert versely impacting operation, reliability, and lifetime of digital items is develop ing, and it'll proceed to extend at an speeded up expense as we search to check our know-how wishes and wishes with our environmental tasks. on the time ofthis writing, which has spanned the latter component to 1989 and early 1990, the problem of selecting a brand new method of generating PW As freed from damaging residues whereas utilizing environmentally applicable production options ap peared to be the key challenge of nearly all of these curious about the broadcast wiring meeting undefined. To many this intended using assorted fresh ing media and/or approach or apparatus improvements; to others it intended the removal of the necessity to fresh via fabrics or procedure changes.
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Extra info for Cleaning Printed Wiring Assemblies in Today’s Environment
These methods are: the copper mirror test, the silver chromate paper (halide) test, the surface insulation resistance test, and the British corrosion test. 1. Test Methods Each of the methods discussed below have specific purposes, advantages, and disadvantages. These will be described along with their procedures. Copper Mirror Test. The copper mirror test is referenced in a number of specifications, and is a measure of a flux's corrosivity to copper. This corrosivity is an indication of the activity level of a flux.
Thus, the requirement is a sliding scale and the gap between it and the control narrows as the control value decreases. This requirement must be met for three different types of comb pattern groups: (1) fluxed, soldered, and cleaned, (2) fluxed, soldered, and not cleaned, and (3) fluxed, soldered with comb face up, and not cleaned. The reason for the third group is to simulate the exposure of the top or component side of a circuit board to flux. This is necessary because some fluxes have been found to be more detrimental when they are not heated to as high a temperature, a situation experienced by flux present on the top side of a circuit board.
6. For temperature and humidity control, one may use either an oven with a saturated salt solution controlling the humidity or a chamber with a microprocessor which controls both temperature and humidity. The latter is preferred simply because there is less maintenance compared to checking a saturated salt solution. Some specifications require minimum absolute SIR values as a pass/fail criterion, whereas others require a minimum SIR relative to the SIR value of a control. A relative value is preferred since it is simply allowing a minimum degradation due to the presence of flux residues.