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SAC solder balls reflow with Sn/Pb paste - Voids Issue

SAC solder balls reflow with Sn/Pb paste - Voids Issue

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hi Dave.F and All, I need to reflow SCA solder balls on Sn/... - Oct 04, 2006 by CW

Change mfgrs of paste OR better yet use pbfree paste, If you... - Oct 04, 2006 by RDR

The main cause of voids is your flux out-gassing during refl... - Oct 04, 2006 by

My soak at 150C - 180C for approx. 85sec to 100sec. I belie... - Oct 04, 2006 by CW

Hmmm.. you are in a pickle then. I have AIM's "Reflow Pro... - Oct 04, 2006 by

what is your peak temp.. if you try to go too high say 225-... - Oct 04, 2006 by

My Peak ~ 228-230C (customer wants to see this temperature).... - Oct 04, 2006 by CW

you may want to try a different MFGR of paste, this does hel... - Oct 04, 2006 by RDR

Any recommendation? ... - Oct 04, 2006 by CW

try Alpha OM5100 this is a noclean paste that we use and hav... - Oct 04, 2006 by RDR

Thanks Russ!!! So, you have NO VIODS at all? ... - Oct 04, 2006 by CW

very minimal at very few locations. We do not Xray every bo... - Oct 04, 2006 by RDR

OK. Thanks!! Lastly, is it the nature of the chemistry ... - Oct 04, 2006 by CW

that question I think I will punt it on over to some of the ... - Oct 04, 2006 by RDR

I have noticed certain BGAs void more than others. We place... - Oct 05, 2006 by Real Chunks

Good morning all. We are able to offer some insight into ... - Oct 05, 2006 by Mario Scalzo - CSMTPE, Dartmouth 6 Sigma Brown Belt

I had horrible experiences with a certain brand on multiple ... - Oct 05, 2006 by

Thanks! What's your ramp rate?2 - 3C/sec? What's your ti... - Oct 05, 2006 by CW

* Try 1.5C / sec from RT to 165C * Hot soak at 165-175C for... - Oct 05, 2006 by Mario Scalzo - CSMTPE, Dartmouth 6 Sigma Brown Belt

Thanks All!! ... - Oct 05, 2006 by CW

Mario, what happens when there are components on the board... - Oct 06, 2006 by

CW, make sure your customer is aware of the affect high te... - Oct 06, 2006 by

Here's the BGA voids-reduction profile that I used: ... - Oct 06, 2006 by

What I usually do is keep the peak temperature about 5-10 de... - Oct 06, 2006 by Mario Scalzo - CSMTPE, Dartmouth 6 Sigma Brown Belt

Solid Solder Deposit may work www.sipad.com mk ... - Oct 13, 2006 by

We had a build that showed a relatively high occurence of BG... - Oct 17, 2006 by PWH

CW, The good news is that you are not trying to use SAC pas... - Oct 26, 2006 by

Thanks!!! ... - Oct 26, 2006 by CW

#44317

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 4 October, 2006

hi Dave.F and All, I need to reflow SCA solder balls on Sn/Pb paste, i get a pretty OK solder wetting and collapse apperance, however, i am seeing voids everywhere, some of them is greater than 25-30%, which has exceeded IPC standard. Please advise.

Thanks!!!

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RDR

#44318

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 4 October, 2006

Change mfgrs of paste OR better yet use pbfree paste, If you are collapsing the balls on the BGA then you are possibly overheating the paste/flux quite a bit. most lead pastes do not like much more than 230 C.

I am assuming that you have a decent profile here, running a soak may help if you are not already

Russ

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C.K. the Flip

#44320

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 4 October, 2006

The main cause of voids is your flux out-gassing during reflow. Try a little "knee" or slight soak in your thermal profile to dry out the volatiles a bit.

Typical soak ranges from 130 deg. C to 170 deg. C for around 30-90 seconds.

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#44321

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 4 October, 2006

My soak at 150C - 180C for approx. 85sec to 100sec. I believe this is sufficient.

I can't change my paste because customer wants to use SnPb paste with SAC solder balls. They claimed that they have sucessful result with other CM.

I need to know if this is typical issue with SnPb on Pb-free BGA?

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C.K. the Flip

#44322

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 4 October, 2006

Hmmm.. you are in a pickle then.

I have AIM's "Reflow Profile Supplement" where they recommend a Low-Long-Soak (LSS) profile for situations like your's. It's an old-school type profiling approach where you ramp up to 120*C for about 1 min. then soak at exactly 120*C for 120 to 180 seconds, then proceed immediately to spike.

You can google this document by typing AIM Reflow Profile Supplement in your search window to see for yourself, what the profile should look like.

If this doesn't work, then have your Program Manager tell the customer that Pb-Free Alloys have a tendancy to void, moreso than Sn-Pb - true story actually! If he/she is a typical PM, that answer'd probably be unacceptable.

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inds

#44323

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 4 October, 2006

what is your peak temp.. if you try to go too high say 225-230 deg C there is a fair chance of seeing voids.. depending on your ball size and paste volume you can get a good collapse at temps below 225deg C...

This message was posted via the Electronics Forum @

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#44324

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 4 October, 2006

My Peak ~ 228-230C (customer wants to see this temperature).

solder ball size - 20mil diameter

Please advise ASAP. Thanks a lot!!!

reply »

RDR

#44325

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 4 October, 2006

you may want to try a different MFGR of paste, this does help on many occasions.

Russ

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#44327

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 4 October, 2006

Any recommendation?

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RDR

#44328

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 4 October, 2006

try Alpha OM5100 this is a noclean paste that we use and have done the same thing you are now, reflowing pbfree with pb paste, we run to max temp of 230C with this paste and use a straight ramp with no soak profile is about 4 mins long from ambiant to resolidification. (183 C)

Good luck bro! Russ

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#44331

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 4 October, 2006

Thanks Russ!!!

So, you have NO VIODS at all?

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RDR

#44332

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 4 October, 2006

very minimal at very few locations. We do not Xray every board but sample them. I think you will find pretty good results here (not perfect)

Russ

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#44333

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 4 October, 2006

OK. Thanks!!

Lastly, is it the nature of the chemistry that Sn/Pb solder mixed with Pb-free alloy will be getting voids? If so, what's the physic/chemistry behind it?

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RDR

#44335

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 4 October, 2006

that question I think I will punt it on over to some of the experts here. I really do not the "why". voids for me have always been related to the escape (lack of) of the "stuff" that is in the paste. I have seen diff pastes perform differently relating to voids with same profile. My beleif is that is flux related oin the paste and maybe be related to the post reflow residue level? More residue = more voids? I think I have seen this but will not bet the farm on it.

Russ

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Real Chunks

#44347

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 5 October, 2006

I have noticed certain BGAs void more than others. We place about 8 different brands of BGAs and only one brand voids like crazy and we have to adjust for it.

reply »

Mario Scalzo - CSMTPE, Dartmouth 6 Sigma Brown Belt

#44359

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 5 October, 2006

Good morning all.

We are able to offer some insight into the problem and offer a recommended reflow profile to solve this issue, but it really depends on the solder paste that you use, as different manufacturers use different boiling point solvents.

In a nut-shell, you must reflow the entire package at Pb-Free temperatures to ensure that the finished joint is a homogeneous mixture of the alloys. Without this, the finished joint may have an intermetallic layer that would also cause enbrittlement. More information can be found at knowledge.indium.com.

Please contact me offline and I can send you the information mentioned above. Should you have any further questions, please don't hesitate to ask. My contact information is below.

Regards,

Mario Scalzo, SMT CPE Technical Support Engineer - Southwest Region mscalzo@indium.com 315-853-4900

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C.K. the Flip

#44374

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 5 October, 2006

I had horrible experiences with a certain brand on multiple types of BGA's (I choose not to mention the brand). The paste was nice and active, but almost to a fault when it came to BGA's.

Finally, I arrived at a profile with a more agressive ramp up (had to get it hotter and faster), and a slight soak zone. I proved that re-profiling CAN help with your voids issue, but it sounds like you're free to shop for other solder pastes anyway. That would be the better option.

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#44376

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 5 October, 2006

Thanks!

What's your ramp rate?2 - 3C/sec? What's your time above 217C. What's your peak temp?

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Mario Scalzo - CSMTPE, Dartmouth 6 Sigma Brown Belt

#44377

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 5 October, 2006

* Try 1.5C / sec from RT to 165C * Hot soak at 165-175C for up to 2 minutes (I'd start with 60 seconds flat soak.) * 60-90 seconds TAL (I's start with 60) * 230-240C Peak.

Thanks, Mario

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#44378

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 5 October, 2006

Thanks All!!

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inds

#44393

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 6 October, 2006

Mario, what happens when there are components on the boards that are not rated to take temperature of 230-240 C Peak for a mixed assembly. I guess there are tons of sn/Pb components that have rated temp of 225-230 C.. So in guess you might want to go for a temp that will form the homogenous mixture and not damage components on board. Ofcourse if the customer has no problem burning off few components that works for us ... :)

This message was posted via the Electronics Forum @

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inds

#44394

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 6 October, 2006

CW, make sure your customer is aware of the affect high temp might have on adjacent components on the board. I guess you must have already checked out the rated temperature of all the components on the board

This message was posted via the Electronics Forum @

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C.K. the Flip

#44398

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 6 October, 2006

Here's the BGA voids-reduction profile that I used:

http://img323.imageshack.us/my.php?image=profileka0.jpg

Keep in mind, this was for Sn/Pb BGA with Sn/Pb solder paste. For your situation, you might want to raise the peak temperatures to at least 225*C - 230*C range. It is true that you may be stressing your smaller thermal mass components beyond their rated temperatures as well as burning off too much of your Sn/Pb paste's flux if you go higher than 230*C for your peak.

Those peak temperatures will successfully collapse and "coalesce" your BGA solder joint, as long as you've spent at least 30 seconds above 217*C (SAC's liquidous point). Whether they help your voids, give it a try!

reply »

Mario Scalzo - CSMTPE, Dartmouth 6 Sigma Brown Belt

#44409

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 6 October, 2006

What I usually do is keep the peak temperature about 5-10 deg C below the peak temperature of my lowest rated component, then set everything else up around that. Worse case scenario is to just extend the time above liquidus (TAL) in 5 second increments until I can get acceptable results.

Thanks, Mario

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Matt Kehoe

#44503

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 13 October, 2006

Solid Solder Deposit may work www.sipad.com mk

This message was posted via the Electronics Forum @

reply »

PWH

#44555

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 17 October, 2006

We had a build that showed a relatively high occurence of BGA voids like you were seeing. It was a very small volume first article that took a long time to get through the line so the paste sat on the boards too long. As we ramped up TACT time in production, the voids went away. No change in process other than time.

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sms_don

#44720

SAC solder balls reflow with Sn/Pb paste - Voids Issue | 26 October, 2006

CW, The good news is that you are not trying to use SAC paste with SnPb balls for that would be a void generator due to the ball being liquidous while the SAC paste is still in a flux cleaning stage.

Two points to consider: One, voids are not an issue even with IPC610D, IPC610C it was, but more data and confidence has given proof that a void is not a failure, but in some cases a crack prohibitor. This just needs to be communicated to the customer as an exception. I have case histories that show this, as long as the voids are centered and not located at the pad surface minimizing contact. The real failure issues with voids will show up in shorts or minimum clearances. Two, the knee profile approach helps if you can control the temperature accurately, the paste types and brands can help to some degree, but the profile is the first means within your control of controling it. Sounds like that 20 to 30% void size is acceptable.

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