Right On,
I agree with the comments on the ENIG nonsense. The only real reason for
ENIG I hear is the ENIG finish is "Flat" compared to HASL.
I don't know what I hear more:
ENIG is really good when the process is good.
Or
I have a bunch of stinking ENIG boards that won't solder right.
I am sticking with HASL.
Bob K
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M.
Sent: Tuesday, September 20, 2011 4:51 PM
To: [log in to unmask]
Subject: Re: [TN] large parts falling off finished surface mount board
assemblies
Robert,
I don't understand your "Given it is a wetting problem to the PCB" comment.
What's wrong with the wetting? Carl's photographs Steve posted see to show
good soldering. The solder paste appears to have completely melted,
dissolved the IAu and wet well to the underlying ENi. There solder fillets
appear to have wet the entire pads and formed good low angle contact to the
PCB pads.
Carl,
If you have not guessed by now I am not a fan of ENIG. There are two
reasons. The first is there have been years of discussion about ENIG
problems concerning BP and brittle failures and where they are similar or
different. The general answer when there is an ENIG problem is the board
shop didn't control their process. What part of the process they didn't
control is never mentioned. All that is said is they didn't control their
process. That means to me that there is not a good handle on exactly what
is causing the problem but something must be causing it and to fix it
control everything. The second reason is that with ENIG you are soldering
to ENi not CU. If one does an Izod Impact test on a solder joint to ENi and
compares it to one done on a solder joint to Cu the results show the impact
strength of a solder joint to copper is better than to ENi.
When I look at the photographs you had Steve post I see an oscillator and an
inductor that stand off the board and when you push on their bodies you
there is a large moment arm and the solder joint fractures. I can't tell
you why the oscillator and inductor on the couple of boards fell off when
you pushed on them and the others didn't. You might find if you put an
greater impact on the oscillators and inductors on the boards you will find
they pop off also.
My guess is if you send the bad boards back to the board shop they are going
to look at the components that didn't fall off and tell you "see the PCB is
okay" "the components that fell off must not have been solder well and the
problem is your assembly process and not the PCB quality".
Good luck.
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 Robert Kondner
Sent: Tuesday, September 20, 2011 2:13 PM
To: [log in to unmask]
Subject: Re: [TN] large parts falling off finished surface mount board
assemblies
Given that it is a wetting problem to the PCB can't we narrow down the
issues here?
1. There was something wrong with the paste. I think this is unlikely.
2. There was something wrong with the PCB. Possible. Plating and
contamination are possibilities.
3. There was a bad reflow profile. Not likely since large components
seemed to reflow OK.
I mean the boards are scrap, right? Lifting a lead and pulling the solder
off the pad is a complete horror story, right?
The only real question is who pays for everything?
Please, enlighten me to the other possibilities! :-)
Bob K.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Reuven Rokah
Sent: Tuesday, September 20, 2011 2:02 PM
To: [log in to unmask]
Subject: Re: [TN] large parts falling off finished surface mount board
assemblies
Hi Carl,
It seems wetting issue. You should do the following:
1. Cross section of bare and assembled boards to measure the Ni and Au / IMC
layers thicknesses .
2. Check bare PCB with the same solder paste used in reflow but without
components, to check wetting.
Reuven
On Tue, Sep 20, 2011 at 7:52 PM, Carl VanWormer <[log in to unmask]> wrote:
> 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.jp
> g 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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--
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*Reuven Rokah*
Mobile: 972-52-60-120-18
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