I will post a handful SEM images to Steve, so you get an idea what it's all about. It may take a while, because he is probably on the market place to buy curtains and wallpaper for his new appartment. Or jogging. Or having a drink on the balcony. /Inge ----- Original Message ----- From: "Inge" <[log in to unmask]> To: <[log in to unmask]> Sent: Thursday, September 10, 2009 5:10 PM Subject: Re: [TN] Need clever comments > Jack &Paul, FYI. > > Today I had a close look at the cross sections. What I found was this: > > 1. The Tin plating was done AFTER solder mask (Jack was right) > 2. The solder mask was very uneven, thickness between 5um and 25 um. > 3. Despite the corrupted surface, the solder mask is homogenous, no > vertical cracks found. > 4. The copper that I found earlier on top of the conductor, i.e. on the > solder mask, that copper had no connection with the conductor copper. > Which means that these contaminations had NOT migrated through the solder > mask. > 5. I can still not figure out from where the copper contaminations come. > > So, all that remains is the question about the copper contaminations tha > embedded in the very surface of the solder mask. I have to adjust my > report and resend it to our customer and the board maker. > > Thanks to your critisism, I can now redo the analys, starting from a more > correct standpoint. > > Your are great! > > /Inge > > > > > ----- Original Message ----- > From: "Inge" <[log in to unmask]> > To: <[log in to unmask]> > Sent: Wednesday, September 09, 2009 8:09 PM > Subject: Re: [TN] Need clever comments > > >> Jack, >> >> SMOBC is the common industrial standard, as you pointed out, however, >> there ARE some fabricators that apply the solder mask after Tin/Lead-ing >> the copper traces. The later method has an obvioius disadvantage, see >> below quoted from an article written by US Environmental Agency: >> >> " This method predominates for several reasons. Copper is a surface that >> lends itself to rigorous cleaning, which is essential for solder mask >> adhesion. Tin-lead under solder mask will liquefy during soldering and >> may cause the mask to blister and peel. The hot air solder leveling >> process generally produces less waste water and introduces less lead into >> the waste water stream than tin-lead plating and reflow. Despite these >> advantages, well-known disadvantages also exist. The shelf-life of hot >> air solder leveled circuits is short and solder thicknesses on pads and >> hole barrels is notoriously difficult to control. For these reasons, a >> small minority of specifications continue to call for tin-lead plate and >> reflow or other alternati air solder leveling, nomenclature screening, >> and finally, gold edge plating if necessary. " >> >> I think that is what happened to our boards....." cause the mask to >> blister and peel"... >> >> Another paper describes Tin under solder mask this way: >> >> " Facility F initially was concerned with the soldermask breakdown where >> the Tin leaches underneath the soldermask....etc" >> >> Quoted from EPA (United States Environmental Protection Agency. >> >> When I started the investigation (had just some hours to spend before >> reporting the result!), I was fully convinced that these boards were >> SMOBC, but our customer said they used tinning before soldermask. I have >> asked for a confirmation from the board fabricator, but got no answer. >> >> Thanks for your comment, good critics. >> >> Inge >> >> >> ----- Original Message ----- >> From: "Jack Olson" <[log in to unmask]> >> To: <[log in to unmask]> >> Sent: Wednesday, September 09, 2009 4:44 PM >> Subject: [TN] Need clever comments >> >> >>>I know I'm late to the game, but I can't resist asking this question: >>> >>>>From my experience, the tin is applied AFTER soldermask, so >>> you have mask over bare copper, and tin over exposed copper. >>> >>> The tin in PHOTO2.JPG in the exposed area looks beautiful, >>> so isn't the question (ignoring the whiskers for the moment) >>> "How can bare copper erupt through the mask?" >>> >>> Unless I missed one of your previous posts, it seems to me that >>> any speculation about copper poking through the tin finish is >>> irrelevant. I'm only addressing Question 2 below, but you mentioned >>> introducing a nickel barrier, and that will not be plated under the mask >>> either, will it? only on exposed circuitry... >>> >>> just wondering, >>> Jack >>> >>> >>> -=-=-=- >>> >>> *Subject:* Need clever comments *From:* Hernefjord Ingemar < >>> [log in to unmask]> *Reply-To:* TechNet E-Mail Forum < >>> [log in to unmask]>, Hernefjord Ingemar <[log in to unmask]> >>> * >>> Date:* Mon, 7 Sep 2009 13:21:54 +0200 *Content-Type:* text/plain >>> >>> >>> Hi all, need some professional backup regarding MIL quality boards. >>> >>> Objects: FR-4 Class III double-sided multi-layer boards, populated >>> with SOICS, BGAs,and a lot of passive components. >>> >>> Observation 1 : the non soldered board have lots of Tin whiskers on >>> inside of the PTH barrel. My thought is this: if whiskers can grow >>> long before the board is assembled, then ain't it likely that even CAF >>> can be generated? See photo 1. >>> >>> Observation 2: Copper has somehow penetrated the solder mask. This >>> can be found everywhere along the conductor traces. You need a very >>> good light microscope and a SEM to see it. See photo 2. >>> >>> Board data: Copper with 0.8 micrometer Immersion Tin. No nickel >>> barrier. Solder mask thickness not specified. >>> >>> Application: Typical MIL-883 environment >>> >>> Q1: What is your opinion about that thin Tin directly on copper? I >>> dislike the concept. Copper is very mobile at high temperatures, and >>> combined with humidity, there can be leakage currents and corrosion >>> issues. Even if the boards are CCd, there is a risk with copper . >>> >>> Q2: I gave the advice to introduce a nickel barrier, but our customer >>> claimed, that they can't because of pressfit connectors and pressfit >>> test pins on the board. Furthermore, they had heard that one cannot >>> have nickel platings when pressfitting, because the nickel will crack >>> and oxidize and cause electrical disfunction. Is this your opinion >>> too? Are there any relevant testing behind such statements? >>> >>> Thanks in advance >>> >>> Inge >>> >>> --------------------------------------------------- >>> Technet Mail List provided as a service by IPC using LISTSERV 15.0 >>> 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 15.0 >> 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 15.0 > 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 15.0 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 -----------------------------------------------------