Bob,
Of course you and NPL (Davide, Chris)were my main sources of knowledge in
this matters, and I thank you all for this and the work you have done.
I know that every assembly has its own problems, and I suppose that I will
have to work hard to have acceptable results.
I somehow have the feeling that this issue is far from being resolved yet,
and that all is fine and interesting as long as you do research, but
Everybody involved in production has to learn the hard way to cope with
these facts.
By the way, I WAS SURE THAT YOU WILL ANSWER ME.
Tomorrow I will send you the cross sections, but I am sure that they will
not be something new for you.
Thanks
Gaby
-----Original Message-----
From: Bob Willis [mailto:[log in to unmask]]
Sent: Monday, July 27, 2009 8:34 PM
To: 'Gabriela'
Subject: RE: [TN] OOPS! The copper is gone!
Assume you sore this the other day on dissolution and the reports?
This is a common problem in the past in my youth and now also in a lead-free
world. Remember its not just capacitors that can have problems. In the case
of capacitors it can be seen in manual soldering and in wave soldering if
there is no barrier layer of nickel.
Any parts without barrier layers may be affected. There are a few examples
of this and standard copper dissolution in the NPL Defect Database. Happy to
add your examples to the site if you like at
http://defectsdatabase.npl.co.uk it helps users to have a good reference
source to defects.
The issue of barrier layers is covered in the report and process guide
produced at NPL with good examples and suggestions on this issue, also
provides examples other parts that can be an issue without a barrier layer
or increasing the thickness of existing barrier layers in a lead-free world.
You can request a copy of the Copper Dissolution Guide and Industry Report
from [log in to unmask]
The content was also covered in my monthly page in Global SMT magazine see
http://content.yudu.com/Library/A18cr7/GlobalSMTPackaging96/resources/6.htm
Bob Willis
2 Fourth Ave, Chelmsford, Essex, CM1 4HA England
Tel: (44) 1245 351502
Fax: (44) 1245 496123
Mobile: 07860 775858
www.ASKbobwillis.com
www.SolderingStandards.com
PCB Design for Manufacture & Assembly Workshop 15th October
www.ASKbobwillis.com
PCB Inspection & Quality Control Workshop 3rd November
www.ASKbobwillis.com/faworkshops.pdf
Book Bob's "Step by Step Failure Analysis Workshop" 4th November
www.ASKbobwillis.com/faworkshops.pdf
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gabriela
Sent: 27 July 2009 18:57
To: [log in to unmask]
Subject: Re: [TN] OOPS! The copper is gone!
Right.
Scrolled the internet for a couple of days, much on copper dissolution
there.
Another present from ROHS.
Luckily we had no delamination because we used high Tg board material, but
also luckily we have no BGA's on it, because my latest information is that
High TG board material is bad for pad cratering. (another present from
ROHS).
I wonder how many cross sections I will have to do in order to validate the
process.
Gaby
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Monday, July 27, 2009 7:39 PM
To: [log in to unmask]
Subject: Re: [TN] OOPS! The copper is gone!
Hi Gaby - you found the unhappy recipe for lead-free soldering: thick
pwbs, lots of thru hole connectors and heavy internal copper layers =
danger of copper dissolution. Both the IPC APEX and SMTAI International
Conference proceedings for the last 2 years have some excellent papers on
the topic of copper dissolution which may be helpful for your issue. You
may need to investigate using a different solder alloy instead of SAC305
(?) to control the amount of copper dissolution. Good luck.
Dave Hillman
Rockwell Collins
[log in to unmask]
Gabriela <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
07/27/2009 11:56 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Gabriela <[log in to unmask]>
To
[log in to unmask]
cc
Subject
[TN] OOPS! The copper is gone!
No surprise at all.
Assembly went through lead free SAC selective soldering. Thick, 20
internal
layers motherboard. Immersion silver plated.
Lots of connectors (not only), populated on both sides. Conventional 25um
copper in holes, outer layers over 1/2 oz copper.
Was soldered before with Sn/Pb.
No free meals, haha.
Want to redesign to ENIG - seems to be the only choice.
I wonder if there is a thumb rule for selecting the possibility of
selective
soldering according to design and platings.
Also, if ENIG is safe for this process, even if rework with SAC ot Sn100
for
hole fill and shorts must be performed.
We will try to overcome the problem, in the meantime by using Nihon
superior, but in order to get good hole fill for such a thick board, the
parameters will be too harsh , I suppose.
Cross sections look very beautiful- pads are gone, knee is gone, barrel is
playing hide and seek, inner layers just end to nowhere.
How did you wise people validate this process and never mentioned anything
on the NET?
Gaby
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