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October 2011

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From:
vladimir Igoshev <[log in to unmask]>
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Date:
Wed, 26 Oct 2011 17:50:16 +0000
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Hi Ioan,

The reason I said "careful" EDS was that the results as always depend on several things. The depth of penetration for a given material will depend on the accelerating voltage and the angle between the electron beam and the sample surface. I'd need to see the actual spectra to tell more.

Yes, FTIR is only good for organic contaminant, but in many cases CAREFUL SEM can show if the surface was contaminated or not. The images you posted don't have enough info to tell what is going on.
Vladimir

SENTEC Testing Laboratory Inc.
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca

-----Original Message-----
From: Ioan Tempea <[log in to unmask]>
Sender: TechNet <[log in to unmask]>
Date: Wed, 26 Oct 2011 13:27:21 
To: <[log in to unmask]>
Reply-To: TechNet E-Mail Forum <[log in to unmask]>,
        Ioan Tempea
	<[log in to unmask]>
Subject: Re: [TN] Discoloration on plated over vias

Cross-sectionning has been done, inside and outside of the orange zones. No significant variation in the Ni layer detected.

FTIR was done prior to sectioning and nothing found. I was told by the lab this method is good for organic residues only and would not detect oxides. I did not argue on the method, since we originally wanted to know if residues from the process were the cause.

The PCB fab said having done EDX and found only Ni and Au (I have the measurements). One question here: how deep EDX penetrates? Wasn't it supposed to pick up the underlying Cu, even under the normal 160 micro in of Ni?

Thanks,

Ioan Tempea, ing.
Ingénieur Principal de Fabrication / Senior Manufacturing Engineer
T | 450.967.7100 ext.244
E | [log in to unmask] 
W | www.digico.cc

N'imprimer que si nécessaire - Print only if you must


-----Message d'origine-----
De : vladimir Igoshev [mailto:[log in to unmask]] 
Envoyé : October-26-11 1:08 PM
À : [log in to unmask]
Objet : Re: [TN] Discoloration on plated over vias

That was exactly what I'd also suggest but from my understanding, some of the sectioning had been done already and at least some information can be pulled out from them.

Honestly, I'd be skeptical about the idea of Cu diffusion, unless the layer of E-Ni is EXTREMELY bad.
Vladimir

SENTEC Testing Laboratory Inc.
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca

-----Original Message-----
From: "Stadem, Richard D." <[log in to unmask]>
Date: Wed, 26 Oct 2011 11:55:22 
To: [log in to unmask]<[log in to unmask]>; [log in to unmask]<[log in to unmask]>
Subject: RE: [TN] Discoloration on plated over vias

A set of microsections directly through some of the affected pads will reveal the thickness of the nickel, and may also reveal information on any hole-fill epoxy smear, lack of planarization, or other fabrication issues that may have caused the root problem; inability to plate the nickel properly.
The way to do this is to microsection the edge of the pad, wet-etch in weak acid, coat in hard, clear epoxy, photograph, microsection again further into the pad, repeat the process and photograph again, etc., until you have at least 4 sectional views.
Most good analysis shops can do this for you. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of vladimir Igoshev
Sent: Wednesday, October 26, 2011 11:42 AM
To: [log in to unmask]
Subject: Re: [TN] Discoloration on plated over vias

Hi Ioan,

Careful EDS may be able to tell. 
Vladimir

SENTEC Testing Laboratory Inc.
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca

-----Original Message-----
From: Ioan Tempea <[log in to unmask]>
Sender: TechNet <[log in to unmask]>
Date: Wed, 26 Oct 2011 12:21:14 
To: <[log in to unmask]>
Reply-To: TechNet E-Mail Forum <[log in to unmask]>,
        Ioan Tempea
	<[log in to unmask]>
Subject: Re: [TN] Discoloration on plated over vias

Once again, thanks everybody for the replies on my problem below.

 

I got one more question:

What test method would indubitably determine if the orange spots are Cu that surfaced?

 

Thanks,

 

Ioan Tempea

 

 

 

 

Dear Technos,

 

I got this issue, see http://ipc-technet.groupsite.com/gallery/21662

 

So 6 layer, 2oz Cu per layer PCB, epoxy filled vias and plated over. After assembly we see 4-5 vias having reddish stains, on most boards. Had it analyzed, no trouble with via integrity, no cracks in cover plating, no migration of fluids from inside out. FTIR does not detect any surface contamination.

 

Au plating thickness stands at 2.09 micro inches.

 

Nothing special detected in the stains, so the lab concluded what we see is an optical effect due to a certain roughness of the Cu. The logical conclusion is no issue, cosmetic defect.

 

However, our end customer, high reliability, want to know what the stains are and want absolute confirmation that long term reliability is not affected. Also, we've been warned that no such issues will be tolerated on future lots.

 

My questions to your infinite knowledge is: have you seen this before? How can I convince the customer everything is OK? What is the root cause and how can I get rid of the issue?

 

Many thanks,

 

Ioan Tempea, ing.
Ingénieur Principal de Fabrication / Senior Manufacturing Engineer
T | 450.967.7100 ext.244
E | [log in to unmask] <mailto:[log in to unmask]>  
W | www.digico.cc <http://www.digico.cc/> 

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