OOPPSS maybe it really is theology not rheology that is getting this to work.....must be a Freudian slip Mike B. > _____________________________________________ > From: Barmuta, Mike > Sent: Friday, July 28, 2006 9:05 AM > To: 'TechNet E-Mail Forum'; 'Stadem, Richard D.' > Subject: RE:(2) [TN] BGAs; SnPb vice SAC Balls > > Gentlemen: As I said you need to develop the correct time, temperature > profile in conjunction with the flux activation system for this to > work properly. If it is set up properly it will not burn off the flux. > Also the theology has nothing to do with it. It's the thermal > activation and decomposition temperature ranges of the flux system > that must be considered. > > You do not need to run a full blown leadfree profile. There is a > middle ground between a standard Sn/Pb and a Pb free profile. The key > is in determining what that is for the particular board design you are > processing > > Yes, components on the board are going to see 230-240C. As I stated, > the problem is getting parts that are compatible with the higher > temps. If you can't you may have to redesign with lower temp parts on > the opposite side of the board as the BGA or if BGA's are on both > sides do a lower temp post reflow. Also you will start seeing more and > more parts with higher temperature ratings from the suppliers. Another > thing is don't take the component data sheet temperature ratings as > gospel. Due to the short duration of time at the higher temps many > components do not have a problem. > > Reballing is certainly an option but if you don't want to screw around > with logistics, added cost, inventory, added supply chain complexity > and reballing quality issues then this is another route to take. These > issues become more of a player when running high volume lean > production. > > I never said it was easy and if you don't have the technical > expertise, material science and resources then choose an alternate > path. > > > Regards > > Michael Barmuta > > Staff Engineer > > Fluke Corp. > > Everett WA > > 425-446-6076 > > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D. > Sent: Friday, July 28, 2006 8:15 AM > To: [log in to unmask] > Subject: Re: [TN] BGAs; SnPb vice SAC Balls > > Danielle, > Yes, excellent point. I do not think anyone makes a 63/37 solder paste > whose flux rheology is intended for those types of reflow profiles. > Thank you. > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of Danielle Casha > Sent: Friday, July 28, 2006 10:04 AM > To: [log in to unmask] > Subject: Re: [TN] BGAs; SnPb vice SAC Balls > > Well put Richard. > > I have one additional comment: I would caution you to watch the ramp > temps with PbSn paste and a Pb Free profile. You may burn off the > flux > too quickly. > > > > Danielle L. Casha > > -----Original Message----- > From: TechNet [SMTP:[log in to unmask]] On Behalf Of Stadem, > Richard D. > Sent: Friday, July 28, 2006 10:59 AM > To: [log in to unmask] > Subject: Re: [TN] BGAs; SnPb vice SAC Balls > > Mike, > I believe the actual melting temperature of the SAC alloy is > more like > 220 deg. C or slightly higher. This means that the other > components are > seeing temperatures in the range of 230 deg. C to 240 deg. C, > because in > order to get the temperature under a BGA to 220 C minimum with > a > longer > TALT, the other portions of the pwb that are more exposed to > the > heat > are (typically) reaching much higher temperatures as a result. > Since you > need to hold this TALT for a longer time in order to achieve > the > more > homogenous alloy mix on the resultant SAC/63-37 mixed solder > joints for > the BGA, you will be subjecting the rest of the components on > the board > to temperatures and dwell times that they should never see. > While your > particular assembly and set of components (including the > printed > wiring > board itself) appear to be holding up to this process and you > have > undoubtly qualified it properly, I doubt that most other > standard SMT > assemblies in the industry can or will. This is why, in > general, > it is > more often wiser to strip off the SAC alloy and reball the > BGAs > if you > are tied to a 63/37 process. There is far less risk to > cycles-to-failure rates using BGAs that are reballed properly > than there > is using mixed alloys and higher reflow temps and TALTS. > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of Barmuta, > Mike > Sent: Friday, July 28, 2006 9:34 AM > To: [log in to unmask] > Subject: Re: [TN] BGAs; SnPb vice SAC Balls > > Bogert: We are faced with the same predicament. As a > manufacturer of > Test and Measurement equipment we are not covered under RoHS. > Hence we > are free to use 63/37 Sn/Pb solderpaste. However we are seeing > more and > more BGA's switching over to SAC only availability. > > Your statement:" There have been published test studies done > that show > that if one solders BGA's having SAC balls in an assembly > soldering > process using traditional Sn63 solder, an unreliable solder > joint may > exist." Is both true and false. > > If you use a traditional Sn/Pb reflow profile it is true. > However the > profile can be modified to increase temperature and duration > above the > 217-219C melting of the SAC alloy. By using the right time, > temperature > and flux activation system you can create a homogenous > dispersion of the > Sn/Pb throughout the SAC solderball. Thus creating a reliable > solderjoint. This is the route we have chosen to take. > > We have conducted metallurgical and reliability testing and > are > continuing to run long term reliability testing of SAC BGA's > with Sn/Pb > solder. We have not seen any reliability issues. > > The real problem is getting all the other components on the > PCA > to > withstand the higher process temps. > > > Good luck on whatever direction you take, I know it's a real > dilemma. > > > > Regards > > Michael Barmuta > > Staff Engineer > > Fluke Corp. > > Everett WA > > 425-446-6076 > > > > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of - Bogert > Sent: Thursday, July 27, 2006 5:16 PM > To: [log in to unmask] > Subject: [TN] BGAs; SnPb vice SAC Balls > > July 27, 2006 > > Folks, I have a dilemma regarding the transition to Pb free. > > As a military user, we have no intention of transitioning to > Pb > free > assembly soldering at this time, and probably never, unless > industry can > positively provide documented evidence, based on accelerated > life > testing acceleration factors, that establish that the use of > Pb-free > solders, such as SAC, will provide a product that will meet > the > same > reliability life requirements that Pb based solders have been > proven to > meet, and that this level of reliability can be easily and > consistently > achieved on the production floor without hiring a "Rocket > Scientist" or > a team of 20 people to establish the soldering process using > Pb-free. > > Given this, I am frustrated by some BGA manufacturers apparent > "Don't > give a dam attitude" about the military users of BGA'S since > some folks > are eliminating Pb from solder balls in favor of alloys such > as > SAC. > Appears they are more interested in their bottom line > industrial > and > commercial customers than us military folks. This is > understandable > since us military folks constitute a very small % of their > overall > business. > > Although some manufacturers will still provide Pb BGA balls, > some will > only provide SAC balls. Also if Pb balls are requested, there > may be > long lead times involved. > > There have been published test studies done that show that if > one > solders BGA's having SAC balls in an assembly soldering > process > using > traditional Sn63 solder, an unreliable solder joint may exist. > > Based on the above, our current intent is to prohibit the use > of > any BGA > that does not use SnPb balls. > > My question is, which is the least reliable alternative. That > is, > allowing BGA'S with SAC balls soldered using Sn63 solder, or > having > someone take the BGAs and have the SAC balls replaced with > SnPb > balls? > > What suppliers have the capability of doing this ball > replacement? > > My preference is to stick with the prohibition on non-Pb BGA > balls. The > down side of this is that by doing this, we may not be able to > take > advantage of new technology parts that may only use SAC balls. > > This Pb free issue is driving up costs. Since about 50% of > the > part > manufacturers are eliminating Pb from their part finishes > without > changing their part numbers, we are forced to implement XRF > testing of > parts received by our OEMs to verify they contain the 3% Pb > mandated by > most military specifications. > > Just because it is a mil spec part does not mean one will not > get Pb > free part terminations. There have been several recent GIDEP > Alerts > that indicate that some mil parts contained pure tin finish, > in > violation of the mil spec. > > While my experience to date is that part manufacturers who > have > transitioned to a Pb free finish such as pure tin have > implemented > tin-whisker mitigation methods, there is no guarantee that all > folks > have done this. Additionally, even though JP002 tin whisker > mitigation > methods can reduce the risk for growing tin whiskers, if one > uses pure > --------------------------------------------------- > 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 > ----------------------------------------------------- > tin, there is no positive guarantee that a tin whisker will > never grow. > > This message (including any attachments) contains confidential > and/or > proprietary information intended only for the addressee. > Any unauthorized disclosure, copying, distribution or reliance > on the > contents of this information is strictly prohibited and may > constitute a > violation of law. 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