Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Blistering issue, mixed LF/SnPb process

Views: 2262

Good afternoon, We run mixed LF/SnPb process for most of ... - Jul 28, 2006 by Pavel Murtishev  

#43024

Blistering issue, mixed LF/SnPb process | 28 July, 2006

Good afternoon,

We run mixed LF/SnPb process for most of out products. Most of chip passives have lead free termination and some of them tend towards blistering issue. SnPb solder wets component in very strange way. Wetting phenomena seems to be abnormal. Please look at next photos:

http://www.yousendit.com/transfer.php?action=download&ufid=D0D74F59399A4704

http://www.yousendit.com/transfer.php?action=download&ufid=44CD17DA56F47A60

Solder gets on the top of the component forming huge void. Fillet form is abnormal. Void inside such filled is really very huge (about 80-90% by volume). Resulting alloy is very soft and can be punched with tweezers easily (photos). I do not think that it is process related issue. For one product we changed the process to pure lead free and defect still remained after that. I never saw such defect before. Defect seems like wicking, but it is not wicking, I�m practically sure. What can it be?

Your help is much appreciated. Thanks.

BR, Pavel.

reply »

Chunks

#43027

Blistering issue, mixed LF/SnPb process | 28 July, 2006

What does your reflow profile look like?

reply »

#43029

Blistering issue, mixed LF/SnPb process | 28 July, 2006

Two lines of thought are: * That you have some solder connections points us towards components. It seems like the solderability protection on some components need to have the reflothermal recipe tailored for that component. * Paste selection is a BIG driver in void production.

reply »


RDR

#43030

Blistering issue, mixed LF/SnPb process | 28 July, 2006

Are all these defects related to the trace that enters pad? Looking at #2, the good fillet has side trace entry and the bad has front entry.

I would suggest that a profile check is in order, then the paste would be next culprit.

Russ

reply »

#43033

Blistering issue, mixed LF/SnPb process | 28 July, 2006

Good afternoon,

Profile is standard ramp-soak-spike (According to paste manufacturer requirements), paste is Almit V16L HM1-RMA, type 3, Sn62Ag2. Look here for details:

http://www.yousendit.com/transfer.php?action=download&ufid=98684D1201B0F001

reply »

#43034

Blistering issue, mixed LF/SnPb process | 28 July, 2006

Good afternoon,

No, defects aren�t trace related. I�ve just posted reflow profile (reply to Chunks). I suspect the component only. All other components are fine. But I can�t understand what exactly happens with this component. I tried to play with soak time to resolve possible wicking issue. No result. Defect rate doesn�t depend on soak time.

BR, Pavel

reply »

Chunks

#43035

Blistering issue, mixed LF/SnPb process | 28 July, 2006

Yur profile looks OK for a leaded paste. It may be tyour paste as stated below. Is this a new problem? Also, have you profiled your oven lately? Could be one zone out of control.

reply »

#43036

Blistering issue, mixed LF/SnPb process | 28 July, 2006

Oven is controlled properly. We run a lot of products at this line. Moreover, same problem appeared at other production line (ovens are different). Yes, problem is new; I never saw this defect before.

BR, Pavel

reply »

#43038

Blistering issue, mixed LF/SnPb process | 28 July, 2006

Good afternoon,

1. Yes, most of all I suspect the components. Could you explain what does mean "reflothermal recipe"? Ramp-to-spike? Ramp-soak-spike? Something special? Thanks.

2. Void is really huge. This voiding differs from "standard" voiding effect. We used lead free solder paste to take off suspicion from solder paste. Defect remained in lead free process also. Fillet appearance was the same (huge void etc.)

BR, Pavel

reply »

Chunks

#43039

Blistering issue, mixed LF/SnPb process | 28 July, 2006

Ah, part issue. Good luck, unless you saw these parts being made, you can only speculate.

reply »


Rob

#43041

Blistering issue, mixed LF/SnPb process | 28 July, 2006

No, you can easily find out if it's a part issue - put down another component with the same footprint(either a chip cap or a different value resistor - like the one in the picture)on the pads where you are having problems and relow as normal. If it keeps happening to the substitute components you know it's not related to that.

reply »

Chunks

#43043

Blistering issue, mixed LF/SnPb process | 28 July, 2006

Hi Rob,

I guess what I meant was if you know it's this resistor that it only happens too, you may have a tuff time finding out why it's only this part doing.

reply »


Rob

#43044

Blistering issue, mixed LF/SnPb process | 28 July, 2006

Sorry Chunks!

Not really with it - Friday afternoon, with 10 minutes to go.

From experience I'd go with termination coating problem, linked a a few values, as they batch coat by value - so a 220R may be affected, but not a 100R.

reply »

Chunks

#43045

Blistering issue, mixed LF/SnPb process | 28 July, 2006

Yes I agree with the termination problem and the Friday thing!

reply »

#43046

Blistering issue, mixed LF/SnPb process | 28 July, 2006

Please. Why over engineer this the end. Simply wave solder them!

reply »

chrisgriffin

#43051

Blistering issue, mixed LF/SnPb process | 28 July, 2006

Thats a great idea Doc. If we all listened to your suggestions, there would be zero defects in PCB manufacturing. I bet your using Bahodum solder which, I'm sure, is incapable of defects.

Pavel, sounds like you can rule out reflow as the problem. Let us know what you come up with.

reply »

#43063

Blistering issue, mixed LF/SnPb process | 29 July, 2006

This recipe is nice for leaded soldering. The time above liquidous plus 20*C is too short for mixed alloy soldering. Remember all that nonleaded stuff that you add to the solder acts to increase the liquidous temperature of the alloy. Try slowing your conveyor.

reply »

#43064

Blistering issue, mixed LF/SnPb process | 29 July, 2006

Well, a "reflothermal recipe" is a typo. It should read "reflow thermal recipe". Sorry for the confusion. Most people call this THE PROFILE. We think a profile is the output of a profiler when it portrays the result of a reflow recipe.

We're guessing that those large voidy areas are the result of the solder not reflowing properly. You need to turn-up the dial on your oven and increase the time the oven sits above 200*C.

reply »

kris

#43097

Blistering issue, mixed LF/SnPb process | 31 July, 2006

Did you try a different lot of components or a different vendor of the components to see if the problem remains ?

reply »

Plasma Prior to Conformal Coating

SMT Equipment