ENIG has its own set of problems. I prefer immersion silver. You still have to be careful not nearly as careful. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Dale Ritzen Sent: Monday, July 07, 2008 8:21 AM To: [log in to unmask] Subject: Re: [TN] Immersion Tin Problem Rex et al, We have had the same problem with white immersion tin finishes. They are to be avoided if you can talk your customer into something else. We are currently in the process of talking with our white tin customer about an ENIG PCB finish. However, if you MUST use them, there are some reflow profiling changes that you can use to successfully do this most of the time (and they will make your process guys go bonkers). They mostly concern running at the lowest end of your Pb-free reflow temperatures (read: so you get MOST of the solder paste "BB's" to flow) and praying that the copper-tin mix on the exposed side doesn't start changing chemically before you reflow it. We have found that minimizing the heated, non-soldered surface exposure to oxygen does help a lot (i.e. nitrogen atmosphere during 1st and 2nd reflow). Plus, we store the boards that have completed the SMT process in a nitrogen cabinet between the SMT and PTH steps of the build. This does slow down the oxidizing effect on the surface of the tin, but it is not the final answer since it does nothing to stop the creation of Tin/Copper intermetallic under heat. Yes, all this extra handling/process control raises the price of the completed assembly significantly. The most effective process is to use brand new boards (no shelf life), speed the product through any/all processes it needs to go through at the lowest temperatures possible (that is tough with Pb-free solders), and minimize exposure to oxygen until the product is finished goods. Actually, the final solution is to avoid immersion tin like the Black Plague... Dale Ritzen, CQA Quality Manager/ISO Management Representative Austin Manufacturing Services -----Original Message----- From: Rex Waygood [mailto:[log in to unmask]] Sent: Friday, July 04, 2008 4:35 AM To: [log in to unmask] Subject: [TN] Immersion Tin Problem We do not usually use Immersion Tin finish boards but we have some with a problem. The boards are about 10-12 weeks old, stored in original packing, double sided PTH and lead free processed. Side 1 processed OK Side 2 had some non-wet problems (Profiles and dwells etc are industry 'norm') Hand soldering has proved to be nigh on impossible. The immersion tin is within the thickness specified (typical values 1.1 to 1.2 micron) Should we have avoided ImSn (as we have done previously)? Is the spec for the ImSn OK? Has the PCB mfr done something wrong? Have we? (apart from accepting ImSn) Rex Rex Waygood Technical Manager PartnerTech Poole Ltd Benson Road Poole Dorset BH17 0RY United Kingdom Tel: +44 (0)1202 674333 Fax: +44 (0)1202 678028 DDI: +44 (0)1202 338222 Mob: +44 (0)7887 997403 [log in to unmask] www.PartnerTech.co.uk ---------------------------------------------------------------------------- --- The information contained within this e-mail and any attachments contained therein may be confidential and/or legally privileged and is for the use of the intended recipient only. If you are not the intended recipient please delete it from your system and notify the sender by return e-mail. The content of this e-mail may not be copied or disclosed to any third parties without prior permission from the sender. E-mail is susceptible to data corruption, interception, tampering and viruses. 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