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Subject:
From:
Vladimir Igoshev <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Vladimir Igoshev <[log in to unmask]>
Date:
Tue, 20 May 2014 10:10:46 -0500
Content-Type:
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text/plain (149 lines)
‎Well, considering the information Carmen provided I wouldn't even think of a solderability issue (manifested after 3 years in service???). 

BP also is out of question as the boards were HASL finished. 

The only thing I can suggest is to do a proper FA. It's always better than speculations based on overall optical images.

Regards,

Vladimir Igoshev
SENTEC Testing Laboratory Inc.
11 Canadian Road, Unit 7
Scarborough, ON M1R 5G1
Phone: 647-495-8727
Cell: 416-899-1882
[log in to unmask]
www.sentec.ca
  Original Message  
From: Stadem, Richard D.
Sent: Tuesday, May 20, 2014 9:40 AM
To: [log in to unmask]
Reply To: TechNet E-Mail Forum
Subject: Re: [TN] Rif: RE: [TN] Rif: Re: [TN] pcb issue led to smt components drop from pcb

It is easy to see it is probably not a reflow profile issue, although some could argue that a longer time in reflow may have improved the IMF to the copper. But if the molten solder wetted and formed a good enough IMF to the component leads and many other pads on the PWB, then it should have wetted to these pads as well.
But because the solder joint is completely formed and seems to have wetted well to the component leads (as you noted) and not to any pad in the pictures, and because of the gray gunpowder-like oxidation residue, my first guess would be a plating issue. 
If it is HASL on copper, then possibly some type of oxidation took place that allowed the HASL finish to coat over the pads, but no real IMF formation ever took place. That is my first guess.
I do not think this is BP; it does not appear to be HASL or solder on ENIG, but I would not rule out that possibility. When I copied these pictures and blew them up and clarified them, it is easy to see grey strands coming off of the edges of the solder joints, almost like a Donald Trump profile shot.
An FTIR analysis of the copper pads is required. A microsection would not be of any use at this stage. The attached pictures only give an indication of the inability of both the HASL and the molten solder paste to form an IMF with the copper pads on the PWB. 
Something is wrong with the solderability (wettability) of the PWB pads, and that is the direction I would go.

Ok, let the argument begin!

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Tuesday, May 20, 2014 9:07 AM
To: [log in to unmask]
Subject: Re: [TN] Rif: RE: [TN] Rif: Re: [TN] pcb issue led to smt components drop from pcb

Hi Carmen!

Finally got your photos! I have them posted now. They are here:

http://stevezeva.homestead.com/1.jpg

http://stevezeva.homestead.com/7.jpg

So, is this happening on multiple boards? The same location on all boards? This looks pretty serious, I wouldn't trust the boards.
Definitely need a cross-section at a minimum to see what is going on...

Steve 


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Carmen Aloisi
Sent: Monday, May 19, 2014 7:17 AM
To: [log in to unmask]
Subject: [TN] Rif: RE: [TN] Rif: Re: [TN] pcb issue led to smt components drop from pcb

Hi Steve
here they are, these are the only kind of components that dop the other ones are well fixed on the pcba.
Thanks a lot,

Carmen



Hi Carmen!

Just reply to this email and I'll post your pictures....

Steve


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Carmen Aloisi
Sent: Monday, May 19, 2014 12:58 AM
To: [log in to unmask]
Subject: [TN] Rif: Re: [TN] pcb issue led to smt components drop from pcb

Dear all
thanks a lot for your promt reply and suggestions, the pcbs have leaded hasl surface finishing I agree with you about potential intermetallic issues... fail pcbas are travelling right now from customer to our plant here in Italy and then I'll make some cross section.

I'd like to share pictures, how shall I contact mr Steve Gregory in order to post them?

Have a nice day
Carmen

Carmen Aloisi
Quality Manager

Eutron S.p.A.
Via Crespi 29 24020 Pradalunga (BG) Italy ph. +39 035697011 fax +39
035697090 m. +39 3355666074 www.eutron.com p.i. 01805190160




Hi Carmen-

You must get the surface analyzed. I believe that it "looks like" bare exposed copper, but the odds are highly against that. As Vladimir has suggested, you can hire an expert to do the whole analysis. Or you can try to make this an educational journey for yourself. If you get the surface analyzed, you'll need an analytical technique capable of identifying the various species and thicknesses of intermetallics which are on the metal surfaces.

Also, you need to understand the usage environment. I believe that with the appropriate amount of temperature cycling, you can get the components to fall off of anything, provided there is a temperature or temperature coefficient of expansion difference between the component and substrate.

Looks like I might be the first to set off some tirades by mentioning "black pad". This is a very ugly intermetallic which is associated with ENIG surface finish, and we providers of electronic assemblies spend many sleepless nights about it because you can have a beautiful joint which fails in even fairly mild usage environments. Obviously we don't have enough information to suggest this as your problem, but it fits the final result (as do many other things!).

Shock will take off SMT components also, but that's usually a negligible probability (exceptions include crystals separating from cell phone motherboards when the cell phones are dropped or thrown).

Can you provide pictures? We like to see pictures in TechNet. You can't broadcast them directly, and we were using some kind of sharing site, but this guy named Steve Gregory takes pride in making it easy to send him pictures and he'll post them. I think the "cc" address in this email is his current one, but he's changed companies a few times, so I'm not positive.
He seems to always watch for opportunities to help like this.

Once you post shots, all of the TechNet experts will come out of the woodwork with additional questions and arguments guaranteed to be somewhat amusing and possibly very educational.

Wayne Thayer

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Carmen Aloisi
Sent: Friday, May 16, 2014 11:48 AM
To: [log in to unmask]
Subject: [TN] pcb issue led to smt components drop from pcb

Hello
I'm new to this forum and I'd like to address the following issue to the
group:
after 3 years from delivery of a batct of pcbas we got back from customer some of them where components are dropping from the pcbas, the solder remains on the component pin and the pads are with exposed copper.
Could you help me in understanding what was wrong on pcb supplier process or on ours?

Thanks a lot in advance
Carmen Aloisi
Quality Manager

Eutron S.p.A.
Via Crespi 29 24020 Pradalunga (BG) Italy ph. +39 035697011 fax +39
035697090 m. +39 3355666074 www.eutron.com p.i. 01805190160


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