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| Subject: Painted on coatings given a 12 month guarantee? | |
Author: Peter Thornton | [ Next Thread |
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] Date Posted: 15:54:38 02/02/04 Mon I have first hand news of a company in England offering a lead free treatment, guaranteed for 12 months, to enable ANY solder pot to run lead free at any temperature. When I stopped laughing I was told the factory offering this service was inundated with customer's pots to be treated. I ask simple questions. Having had a few years' experience in surface coatings, gleaned from silicon wafer epitaxy reactors, ion implanter wafer holders and such, I know that something as reactive as tin at 260 deg.C is one hell of a soluent. And a "paint on coating" even with a guarantee isn't worth the paper it's written on. 1) Does this coating affect joint reliability by introducing ionic components causing long term corrosion... remember purple plague...? 2) Does this coating work at extended temperatures... >260C? Or do you have to keep temperatures very low, with bad wetting and pull through to top side? 3) Can a painted on coating (2um thick at best, in the weakest place) cope with the abrasion of the force pumped solder... remember, it contains dross and other oxide products, all very abrasive? 4) Does the 'paint on' coating work on pump shafts, where the continuous rotating / friction dross oxygen enrichment occurs? 5) Ask if the guarantee covers consequential liability. If you don't discover a flaw in the painted on coating before you send out boards, you have made joints with metallic contamination... and you won't know until the failures come flooding back in, too late to make amends? 6) You must make your own decision. If you can take a risk, chance your output quality on a cheap, paint on coating, ok: do it. I will take a metalurgically proven, time tested, quality assured solution: if you regard quality as a first issue, you should do the same. Trust silicon carbide / nitride. Silicon wafer epitaxy susceptors run this coating day in, day out in an atmosphere of HCl / Hydrogen (an extremely reducing & corrosive mixture) at 1250 deg.C with no problems... talk to a wafer fab. process engineer in Epitaxy / Diffusion if you don't believe me. email t_eeco@hotmail.com for more information. [ Next Thread | Previous Thread | Next Message | Previous Message ] |