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Uncoalesced solder problem in fine pitch IC pads

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hai, we r using type 4 solder paste in our pcb assembly pro... - Sep 06, 2008 by ramesh.r  

#56374

Uncoalesced solder problem in fine pitch IC pads | 6 September, 2008

hai, we r using type 4 solder paste in our pcb assembly process - we are now facing the following problem. 1. two component pads soldering was seemed uncoalesced soldered joint except all the other components. 2. what will be the problem & solution for this above mentioned prolem.

Can any body provide us solution.

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#56376

Uncoalesced solder problem in fine pitch IC pads | 6 September, 2008

We can't help but wonder: * What are the measured temperatures on a good solder connection and the picture connection? * Why use use Type 4 solder paste?

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#56379

Uncoalesced solder problem in fine pitch IC pads | 7 September, 2008

Does look like a poor reflow profile needs to be hotter, is it Pb free

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#56382

Uncoalesced solder problem in fine pitch IC pads | 8 September, 2008

1.The Temperature on the pad is 247.C & also it is an lead free profile, the same profile we have used till last lot but we had obsereved this problem earlier to this current batch. 2. Both in Type3 & Type 4 paste we are using because of we are using the micro bga in this PCB.

3. I had analysed the bare PCB & obsoved the following. a).the PCB manufactured before 15 months. b).the pads ( land area )ics found to be fungus formation & some pads found oxidised.

From the above analysis , i found to be confused that what was the possible cause for the uncoalesced soldering problem.

can any body help us.

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#56386

Uncoalesced solder problem in fine pitch IC pads | 8 September, 2008

Here we go with another "solderability problem". How do you know the pads on the bare PCB are oxidized? Just based on its colour? If that is the root cause, then why ohter parts on the same board are fine?

If you want to solve the problem, get it's analyzed!!!

Regards,

Vlad

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#56397

Uncoalesced solder problem in fine pitch IC pads | 8 September, 2008

Of the six pads in the picture, which are the two that are unacceptable?

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#56400

Uncoalesced solder problem in fine pitch IC pads | 9 September, 2008

God..... give it a rest.

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#56408

Uncoalesced solder problem in fine pitch IC pads | 9 September, 2008

I wish i saw at least one problem posted here being solved by the "knob turning" technique

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#56422

Uncoalesced solder problem in fine pitch IC pads | 9 September, 2008

Perhaps people are solving their problems by turning knobs and thus not finding the need to post here.

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#56425

Uncoalesced solder problem in fine pitch IC pads | 9 September, 2008

May be you right, but I spend a lot of time on Technet (a similar site maintained by IPC) and people who posted questions usually come back saying whether the problem has been solved, as someone else may face a similar problem down the road. I think it'sa good "habit". Don't you agree?

Regards,

Vlad

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#56431

Uncoalesced solder problem in fine pitch IC pads | 10 September, 2008

In the real world where I work, I turn knobs (really key boards, mouse, or touch screens) every day to solve solder related problems. I can tell you exactly why I have to for each one I adjust.

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#56433

Uncoalesced solder problem in fine pitch IC pads | 10 September, 2008

And I bet you are not alone :-). All I'm trying to say is that there are problems which can be fixed by knob turning, but there are also others which can not. So, the appropriate analysis should be done to find the root cause and fix them.

In the real world where I work, I see the both types all the time. I'm not sure whether you saw it or not, but I posted some images showing a "solderability problem" in one of the treads (it's the longest one for now) asking whether it could be fixed by knob turning (I knew it couldn't).

Regards,

Vlad

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#56434

Uncoalesced solder problem in fine pitch IC pads | 10 September, 2008

You missed my point.

People often don't find the need to post their problems here to begin with because "knob turning" solved them *before* they needed to lean on the collective experience of SMTnet, Technet, or what-have-you.

Your posts seem to be saying that if you have a problem, get the board analyzed at the outset to eliminate any question as to whether or not there is contamination, oxidation, etc.

While knowing up front if there is a material issue would be great, getting to that point is costly, and with the number of times I've had true solderability problems with either parts or boards, I'll put my money on finding another solution first, for far less cost.

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#56435

Uncoalesced solder problem in fine pitch IC pads | 10 September, 2008

Amen to that!!!

When I was still on the production floor and had problems I couldn't go to the production manager and tell him/her we had to shut down the production line and have the boards send in for analyses. (He/She would have seriously questioned if I was the right person for the job)

I would have been told that solderability issues could be avoided by proper vendor qualification and/or incoming inspection.

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#56436

Uncoalesced solder problem in fine pitch IC pads | 10 September, 2008

True words of wisdom. Production managers need product out the door, not tied up in wip waiting on an analysis to go and fight a vendor for errors in their manufacturing. Especially if you are a Low Vol High Mix facility. Quite frankly, the resources are not available to send problems out for an x amount of time for analysis. Solutions need to happen in real time and as quick as possible.

I do want to mention though that I wish there was enough resource for analysis. I think that it is a pretty cool thing when allowed. I dont knock what you do. I think myself and most others are just giving real life testimonies to the work environment in most facilities that demand solutions from their engineers, by their engineers and faster than they ask for it.

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#56437

Uncoalesced solder problem in fine pitch IC pads | 10 September, 2008

Am glad we got that straight

There is a big difference between the �real world� and the �ideal world�.

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#56438

Uncoalesced solder problem in fine pitch IC pads | 10 September, 2008

Dave,

I don't think you will get a response in the mean time he found the right knobs to fix the problem.

Sorry couldn't resist

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#56440

Uncoalesced solder problem in fine pitch IC pads | 10 September, 2008

No arguments there. I 100% agree that quality engineers can and do solve a lot of problems on the spot. I've nevern said "run an analysis as soon as you get a problem".

The whole nine yard started with a solderability problem. In my previous production environment, if guys on teh floor get a solderability problem they would bring it to us (the lab) to figure out what is going on for a very simple reason: the parts had been previously qualify (we ran solderability tests with wetting balance for incoming), so somthing must be wrong. In the majority of the cases, the solution wasn't in the turning the SMT process.

So, what I've been saying is that there are cases when the problem can not be fixed on spot and that is when one would want to send it for analysis.

A turn around time is a legit concerned, but it always works out with our customers to their advantage:-)

Regards,

Vlad

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#56445

Uncoalesced solder problem in fine pitch IC pads | 10 September, 2008

I am dealing with a similar uncoalesced solder issue. This defect has come and gone several times during the last 6 months. See image. In my case, I am using conventional SnPb solder and an entire strip of my OSP finished board (includes various device; types, sizes and lead finishes) shows some evidence of uncoalesced solder. I am using a Rheopump and I suspect separation of the metal and flux vehicle as the Root Cause. Can anyone offer any supporting evidence for this suspicion?

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#56446

Uncoalesced solder problem in fine pitch IC pads | 10 September, 2008

"I 100% agree that quality engineers can and do solve a lot of problems on the spot."

*cough*

*snicker*

Or did you mean "engineers of high quality"?

By and large, the QE's that I've worked with only found, identified, highlighted, or conjured up problems. Never had one actually solve one.

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#56447

Uncoalesced solder problem in fine pitch IC pads | 10 September, 2008

Should have sent them in for Xray/microsection Steve that sorts out the QA guys over here

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#56448

Uncoalesced solder problem in fine pitch IC pads | 10 September, 2008

Do those Balls pass IPC LOL Looks like the paste has been stored incorrectly probably stored stood upright and the flux medium has 'moved' so you have very rich flux areas and getting slumping due to it. Paste in cartridges should be stored flat refrigerated and turned daily.IDEALLY Or you have not printed it but flicked the paste onto the board Cheers Greg

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#56450

Uncoalesced solder problem in fine pitch IC pads | 10 September, 2008

At the risk of painting with too broad a brush: QEs are like seagulls: fly in, make lots of noise, crap all over things, then fly away.

Back to the knob turning vs. analysis debate. Part of it may be different industries. We're in the high reliability industry where there are safety and very expensive warranty/recall penalties for sending bad product out the door. If we turn a knob it may just mask the problem and we could be sending walking wounded out the door. When we solving a problem we have to be absolutely sure it's really solved.

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#56451

Uncoalesced solder problem in fine pitch IC pads | 10 September, 2008

"When we solving a problem we have to be absolutely sure it's really solved."

Conversely, it's always good to return things back to the way they were when you conclude that THAT knob turn didn't solve the problem.

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#56452

Uncoalesced solder problem in fine pitch IC pads | 10 September, 2008

To me it speaks about teh quality of the engineers. I[ve seen both types, though

Vlad

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#56453

Uncoalesced solder problem in fine pitch IC pads | 10 September, 2008

And doing analysis you are NOT changing things.

Vlad

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#56465

Uncoalesced solder problem in fine pitch IC pads | 11 September, 2008

Paste stored tip down, so separation in the tube is not suspect. Remember that the defect was produced on a screen printer running with a Rheopump. A few more details are that the strip of the board containing the uncoalesced solder is consistent with the direction of the pumphead travel. There is also an area of the pumphead that extends about 2" past any apertures (no direct paste depletion). On the other side of the uncoalesced strip there is step for a thick stencil area (8-10mils vs. neighboring 5-6mils). The thick stencil area is needed to attach a connector using the pin-in-paste method. This is a relatively large automotive connector (Pin Field ~1" x 6") that extends nearly the length of the board. Summary - Uncoalesced solder was observed in a strip between the connector and a parallel edge off the board, in the direction of print head travel and the pumphead overhangs the board by about 2� near the uncoalesced solder). Does anyone have any evidence supporting a theory that the uncoalesced solder may have resulted from paste separation in the pumphead.

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#56466

Uncoalesced solder problem in fine pitch IC pads | 11 September, 2008

Sorry all I know is that storing the paste Tip down the flux will run to the tip of the cartridge so will be runny initially then dry up as you use the cartridge. Unless the Rheopump mixes it before application

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#56467

Uncoalesced solder problem in fine pitch IC pads | 11 September, 2008

Flux is less dense than metal so it 'floats' to the back NOT the tip when the tubes are stored tip down.

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#56469

Uncoalesced solder problem in fine pitch IC pads | 11 September, 2008

ISSG, I didn't see you mention anything with respect to profiling. Should we assume that you've already ruled out any thermal issues?

Based on the proximity of your problems to a big honkin' connector that's where I'd have looked first.

But then again, I'm a knob turner. ;)

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#56470

Uncoalesced solder problem in fine pitch IC pads | 11 September, 2008

Yes sorry you are right so you have answered your own question anyway. Dry to start runny at the end

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aj

#56471

Uncoalesced solder problem in fine pitch IC pads | 11 September, 2008

Hi,

I had similar problem a while back.

Diagnosis was a combination of two things:

1 - Gold thickness was below spec. which gave us solderability problems. There should be other areas of the board that show signs of this.

2 - The devise in queastion had too small of a footprint - in other words the lead width was wider than the pad itself. This contributed to the lead attracting more solder than it should.

aj...

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#56473

Uncoalesced solder problem in fine pitch IC pads | 11 September, 2008

YES! Reflow Profile knobs have been verified.

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#56479

Uncoalesced solder problem in fine pitch IC pads | 11 September, 2008

I'm curious how many knobs have left to be turn? :-) Isn't time an issue in a production environment?

Vlad

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#56486

Uncoalesced solder problem in fine pitch IC pads | 11 September, 2008

For Production purposes, the problem goes away when a new solder paste lot is used. As I reported in my first message though, the problem keeps coming back. Most likely, paste lot is not the Root Cause (3 different lots now in the last 6mo). I really want to know whether anyone has any supporting data for a theory that paste separation in the Rheopump as it is used with my board is the true Root Cause.

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