Sona: Back in the "old" days we did a lot of tin plating as the final finish on Teflon MLB's, typically for high frequency signal generators. You definitely didn't want to mess these up or it could get real expensive rear quick. It's a very tricky process but if all factors are controlled properly it works. Unfortunately most people doing tin plating these days are only using it for etch resist and are not aware of the multiple issues needed to produce an acceptable electroplated tin final finish. So let me give you some pointers on how we did it. 1. Bath Type: Lea Ronal(Rohm and Haas) Bright Acid Tin Sulfate Electrolytic Plate. This is a fine grain structure finish not requiring any type of reflow processing. Due to low porosity and tight grain structure of the deposit it is not as susceptible to staining as a matte/semi-mate tin. 2. Underplate: To help prevent slivering you need an electrolytic nickel underplate between the copper and tin 3. Rinsing: To minimize staining after tin plate you need multiple rinses cold followed by hot. Any acid drag over in final rinsing will result in staining. 4. Resist Strip: The resist stripper chemistry has to be designed for compatibility with bright tin, if not you will get staining. 5. Etch: You need to control your etcher(ammoniated), pH, chemistry, temp, speed, etc, to minimize undercut which will produce slivers. Again rinsing is critical here too. 6. Soldermask Prep: Do not scrub the panels. 7. Soldermask Bake: Bake at 140C for 60-80 mins AT temperature. If you have discoloration you probably have done a poor job of rinsing somewhere above or have poor water quality. Poor air circulation in the oven can also be a cause. 8. Tin Plate Bath Control: Control of the multiple component organic brightners, levelers and grain refiners is critical. Also the stannic, stannous, sulfuric acid constituents, cathode agitation, amount/velocity of filtration, trace metal impurities, organic build-up, etc, need to be monitored and properly controlled. If done right the end result will be an acceptable product but screw up just one factor and you will have garbage. You need to ask yourself how much you are willing to commit to offer this type of final finish and is it worth it. Regards Michael Barmuta Staff Engineer Fluke Corp Everett WA 425-446-6076 -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Fineline Circuits, Inc Sent: Friday, October 14, 2005 9:39 AM To: [log in to unmask] Subject: Re: [TN] Electrolytic Tin Plating Colin: 2-3 years back we ran an experiment with a tin vendor where we did electrolytic tin plate, etch, and mask.Tin was supposed to be the final finish per vendor.Vendor told us that he had customers that did this. However the tin got tarnished and dark grey after cure and we just did not like the look off the final finish. We did not pursue it further. Sona ----- Original Message ----- From: "Colin McVean" <[log in to unmask]> To: <[log in to unmask]> Sent: Friday, October 14, 2005 10:33 AM Subject: Re: [TN] Electrolytic Tin Plating Are you suggesting that you use the tin plate as your final finish? I'm no chemist, but I think that could spell trouble, with the open structure of the electroplated tin giving rise to whiskers. We use Electroplated tin, but only for the etch resist application - we strip it off, solder mask, then final finish, either Immersion Silver, Immersion Ni/Au, or lead free HASL dependant on customer requirements. Colin McVean M.Inst.C.T. Production Manager Artetch Circuits Limited Main: 01903 725365 DD: 01903 712926 Email: [log in to unmask] www.artetch.co.uk -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Fineline Circuits, Inc Sent: 14 October 2005 15:20 To: [log in to unmask] Subject: [TN] Electrolytic Tin Plating Hi Technetters: Now that Leadfree is here or close to, we would like to change the electrolytic tinlead plating tank to electrolytic tin tank. I would like to know if the other fab houses have done this and if so which vendors tin chemistry has a wider window of operation. Are they seeing any tin whiskers/sliver problems etc..especially if the boards are stored for few months. Also it is my understanding that you can mask over this plated tin since it does not flow. In this case you can totally avoid stripping the tin and tin levelling. We currently do offer other finishes including electroless tin , immersion nickel/gold, silver.... If there are other consideration in making this change I would appreciate your input. Franklin, like you I would like to see more fab houses participating but I would like to remain with technet. Thanks Sona Sitapara Fineline Circuits Inc. --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------