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
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