My guess is you have a bunch of bad PCBs and every board built is a likely
potential failure.
You might take some bad board, those on which you can pop off leads, and
give them a long slow reflow. If that "Mixes Up" the solder to metal
interface it might help.
It does not sound good. I would not want any of those boards in my system,
reflow or no reflow.
Bob K.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Carl VanWormer
Sent: Tuesday, September 20, 2011 12:53 PM
To: [log in to unmask]
Subject: Re: [TN] large parts falling off finished surface mount board
assemblies
If this really is a PCB problem, is there anything the assembly house can do
to mitigate the problem? Is there an easy (nondestructive) way to tell if a
board will have this problem?
Thanks,
Carl
-----Original Message-----
From: Wenger, George M. [mailto:[log in to unmask]]
Sent: Tuesday, September 20, 2011 6:58 AM
To: TechNet E-Mail Forum; Carl VanWormer
Subject: RE: [TN] large parts falling off finished surface mount board
assemblies
Carl,
The pictures indicate you have a brittle fracture at the ENi/Ni-Sn IMC/
Solder interface.
Regards,
George
George M. Wenger
Senior Principal Reliability / FMA Engineer Andrew Corporation - Wireless
Network Solutions
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 Office (732) 309-8964 Mobile
E-mail: [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Carl VanWormer
Sent: Tuesday, September 20, 2011 9:51 AM
To: [log in to unmask]
Subject: Re: [TN] large parts falling off finished surface mount board
assemblies
Steve has posted pictures of my PCB failures on his site. Upon further
examination, prompted by several suggestions from the group, I have found
that the solder seems to stay with the components, leaving just the dull,
fine granular surface that seems to be the actual pad texture without any
Gold showing on the top surface. Does this mean that the Gold combined with
the solder (as expected), and then the remaining
solder/Gold/Nickel/inter-metallics (Technet words I picked up) boundary
failed?
We have seen 2 bad assemblies (from this batch of 30) that failed in this
manner, and 5 good assemblies (still in our stock) that take significant
force without failures. We are in the process of checking any more
assemblies we can locate.
- What made these bad boards different from the others in the same
production run?
- Can these bad boards be "fixed" by re-processing through the IR oven?
- How can I keep this from ever happening again?
Any more thoughts, hints, and/or opinions are appreciated.
http://stevezeva.homestead.com/csi1-pads_and_solder_on_leads.jpg shows a
crystal that popped off with medium fingernail pressure. Almost all of the
solder stayed on the leads, with the surface of the PCB pads left flat with
no major accumulation of solder.
http://stevezeva.homestead.com/csi2-pads_and_solder_on_leads.jpg shows an
inductor that popped off with medium fingernail pressure. Like the crystal,
the solder stayed with the inductor pad. It could be peeled of the inductor
pad with the knife blade. When the knife blade was scraped across the PCB
pad, there was no significant quantity of solder, and the hard granular
surface made a much "harder" scraping sound.
http://stevezeva.homestead.com/csi3-pads_after_component_popped_off.jpg
shows the pads where a SOT-23 transistor was popped off, leaving similar
no-solder PCB pads with all the solder left with the good looking fillets on
the SOT-23 leads.
http://stevezeva.homestead.com/csi4-pad_before_soldering_thumb.jpg shows a
bare board pad, before the soldering process.
http://stevezeva.homestead.com/csi5-pad_after_component_popped_off.jpg
shows the same position, after the pad has been processed, then the
SOT-23 had been popped off of that pad. There was no significant
accumulation of solder left on the PCB pad.
Thanks,
Carl
-----Original Message-----
From: Steve Gregory [mailto:[log in to unmask]]
Sent: Monday, September 19, 2011 3:32 PM
Hi Carl,
Send me some pictures and I'll post them...
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Carl VanWormer
To test this possibility, I wedged the X-Acto blade under the plastic
package of a SOT-23 transistor. A pin lifted up. I held that pin down with
a fingernail, re-inserted the blade, and the other two pins popped off the
board. All 3 pins had solder blobs the shape of the pads, and all 6
surfaces were uniformly granular.
Does anybody want to see some pictures? If so, I can try to get some to
Steve.
Thanks,
Carl
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Goodyear, Patrick
I'm with Phil, sounds to me like the thermal mass on the component was too
large for the 'BIG' components to fully heat and they never actually got a
melt or good reflow, due to too short a dwell time, the only thing that was
holding the component on was the binder in the flux in the paste which had
slightly solidified with a minor melt. But that is just a guess.
Pat
Pacific Gas and Electric
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Bavaro
I might have missed something but are you sure the solder actually melted?
It almost sounds as if the bottom side heaters in the reflow were off and
you only got topside heat applied. You should not have been able to see any
yellowish metal beneath the solder connections.
-----Original Message-----
From: Carl VanWormer <[log in to unmask]>
A surface mount PC board assembly (made by a local assembly house and passed
by our outgoing test) was returned from the end user, along with an
electrolytic capacitor that they had "knocked off" the board. After looking
at the assembly and component under a microscope, I noticed that the "gold
plated" PC board (Lead free) had a fine granular solder appearance (much
smaller grain than solder paste balls) on the pads newly exposed, with the
whole "melted solder" blobs (in the shape of the
pads) attached to the capacitor leads (with a similar granular appearance).
After minor scraping of various parts, I had come to no brilliant
conclusions, so I pressed my finger nail against an inductor that was of
similar size to the capacitor. It popped off the board with the same
symptoms as the capacitor. After recovering from my surprise, I realized
that I have no clue about the causes or cures for my component adhesion
problem. Can any of the more experienced members of this fine group direct
me to some key words that might lead me to a quick education (and solution)?
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