Hi, OSP is more subjected to erosion issue especially (rework) in Plated-Through-Hole processes.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of HuGause
Sent: Friday, 4 January 2008 3:33 PM
To: [log in to unmask]
Subject: Re: [TN] OSP w selective gold
Hi Genny,
Ryan's information is very comprehensive.I concur w/ them and some of my experience share as below:
1. OSP is a good solution for lead free products, about 30% PCB use OSP as surface finishing. For lead free high temperature reflow application, some of the conventional OSP may not work, you shall use the high temperature compatible OSP chemical,like Entek Plus HT, or Gilcoat-SMD F2(LX).
2. The ICT probe ability maybe a concern, the OSP thickness control is important.
Best Regards,
Gause
> Date: Thu, 3 Jan 2008 17:52:11 -0700> From: [log in to unmask]> Subject: Re: [TN] OSP w selective gold> To: [log in to unmask]> > Hi Genny,> > OSP is actually the "preferred" finish with selective gold because you> do not need to mask the gold in order to apply the finish.> > Of course, there are gotchas!> The OSP solution tends to precipitate out onto the rollers of the line,> which then transfers as big globs onto the board, if the line is only> run occasionally. Suppliers who run the OSP line continuously don't see> this problem very much.> > Certain OSP formulations carry copper into the solution and transfer it> onto the gold, causing it to discolor. (The more common OSP> formulations don't have that problem.)> > OSP has a limited shelf life.> > OSP does not like to be baked. Baking your boards for 24 hours at 125C> will render them unsolderable, so beware!> > On the positive side, you can have boards recoated with OSP to restore> the solderability. So if you store boards!
for 2 years, or bake them to> unsolderability, you can send them back to the supplier and they will> restore the solderability by micro-etching the copper and reapplying the> OSP.> > Which brings up another gotcha. Since each OSP application involves a> micro-etch, too many times through the OSP application will> significantly reduce the copper thickness in the vias. So you will want> limits on the number of times boards are allowed to go through OSP> application. Sometimes the board shop will re-work boards through the> OSP line before you even get them the first time!> > Many board shops do electrical test before OSP because the OSP causes a> high number of false failures. This means the micro-etch in the OSP> process can open up marginal vias, but there won't be a test to catch> the opens. Instead, the open vias will be caught after you assemble the> product.> > The OSP micro-etch presents a "risk" of chemical entrapment if your vias> are tented on only one side.> > Sold!
erability through the wave is marginal and more difficult to get top> side fillets.> > Exposed copper surrounding a solder joint is common. While this isn't a> problem, just be aware that the solder will not wet all the way down the> sides of pad, or to the corners, etc..> > Solderability is not as good as ENIG or imAg, so marginality in the> soldering process will appear sooner.> > The OSP can usually be removed by the stencil/board wash system.> Getting washed boards back to the line is not especially time critical,> but don't expect to wash boards and put them back into inventory to sit> for a long time before re-use.> > The copper will discolor like it is oxidizing (because it is) after each> reflow. Don't be alarmed! It still solders.> > OSP will not hide the galvanic effect that occurs during the gold> plating process, so some SMT pads will appear oxidized because their> surface texture will be rough. Don't be alarmed! This is typical when> there is a large difference !
in surface area between the gold plated pad> that is connected to a non-gold plated pad. It doesn't noticeably> affect solderability.> > There are probably other gotchas, but I can't think of them right off> the bat...> > > In spite of these gotchas, OSP still works quite well and has the huge> advantage of simplicity for the PCB supplier; and you are soldering to> copper instead of nickel compared with ENIG. For most shops, this is> the cheapest finish, especially if you require selective electroplated> gold. You don't need any "special" handling criteria except what was> stated above. Nitrogen is NOT needed for soldering to OSP, and I really> haven't seen any no-clean solder paste that has a problem with OSP. In> other words, soldering to OSP is not difficult.> > Good luck.> Ryan> > -----Original Message-----> From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard> Sent: Thursday, January 03, 2008 3:22 PM> To: [log in to unmask]> Subject: [TN] OSP w selective gold>!
> We have never used OSP for anything, but we may be required to switch> one of our products to it. Can anyone point me in the direction of some> good solid info regarding working with this finish? > How common is it, especially if you need selective gold? Are there any> solder process pitfalls to watch out for? > This is for leadfree products.> > Thanks in advance,> Genny.> > ---------------------------------------------------> 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> -----------------------------------------------------
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