no-clean processes - are gloves necessary?| 21 October, 1999
Does anyone have any info in regards to wearing gloves, finger cots in a no-clean process? Are there ionic contamination levels that validate the costs involved in setting up a system? Appreciate any feedback -Rich
Re: no-clean processes - are gloves necessary?| 21 October, 1999
An excellent question and one which is often totally ignored. If you wish a "no-clean" flux to be as safe as it possibly can be, the PCB and the components must all be contamination free (ionic and non-ionic). Only then can you be sure that the residues are as safe as the flux manufacturer intended. Unfortunately, it is only too frequent that the components (including the bare board) are delivered to the assemblers with deplorable amounts of contamination which can not only remain through the soldering/reflow process, but they may also interact with the flux chemistry, reducing its efficiency. The same applies to handling contaminants.
I have always said that "no-clean" is not what the name implies: it displaces the main part of the onus of cleanliness responsibility from the assembler to the suppliers. Unfortunately, we assemblers tend to live in our little microcosm, blithely ignoring what goes on behind the scenes before or after (unless something goes seriously wrong). This is sometimes acerbated by Purchasing who prefer a supplier who is half-a-cent cheaper per $5 IC but not knowing his components have an ionic contamination of 12 �g/cm2 eq. NaCl, as against 1 �g/cm2 eq. NaCl for the slightly more expensive one. If you think I exaggerate, come down to earth: I have measured ICs and other components at over 20 �g/cm2 eq. NaCl AND bare boards at over 10 �g/cm2 eq. NaCl. IMHO, the figure for both should be less than 1 �g/cm2 eq. NaCl if you are not going to do a post-clean, for most applications involving professional electronics. This is part of what concurrent engineering is all about because the bare board and component manufacturers, along with purchasing should be brought into the pre-production phase, so that they know your requirements (and why I have checked that this message should appear in other relevant forums). My guess would be that at least 50% of subsequent problems on a properly designed assembly which is not cleaned are due, at least partially, to contaminants present before soldering.
So, to reply to you, if you are producing something where you expect a modicum of good service life, especially under poor operating conditions, the effort and cost of using at least white cotton gloves (the cheap chuck-away types are good enough) is justified, as well as making sure your suppliers give you clean components.