Thanks for this info. It raises a number of questions in my mind. Would
US affect the peel strength of very fine tracks (<100 µm)? If so, energy
intensity at the board, frequency(ies)? etc.? I can easily imagine that
an imploding cavity close to the track could shake up a tenuous bond,
where the copper treatment is dimensioned so that the pitch between
asperities is > the track width. I think this is a subject that could be
looked at by someone???? Perhaps by Gould or one of the other copper
"makers"??? Maybe it needs a new treatment??? Then, what about HDIS
additive copper???
Brian
Ryan Grant wrote:
> O.K. all you nay-sayers, I'll back up Paul's statement. Based on
> internal data, a single digit DPM failure rate on BGA's was finally
> traced back to our 40kHz "Sweep Frequency" 500W transducer stencil wash
> used to clean misprinted boards. It took several years, numerous DOE's,
> and millions of assemblies to finally trace the root cause to the
> ultrasonic cleaner. One of the reasons the cleaner was overlooked for
> so long, is that we still don't have a working theory of the physics
> behind the failure. PARTICULARLY because "bare boards", without any
> components, that are washed in the ultrasonic cleaner will end up with
> broken solder joints on BGA's. The failure mode is separation of the
> BGA land pad from the laminate and it is extremely dependent on the land
> pad size, as well as other dependencies such as package design and PCB
> layout. We don't see the effect when the land pad is larger than
> 0.29mm. And yes, we are very aware of all the other confounding effects
> that also cause pad separation when the pad size is smaller than 0.29mm.
> We suspect there is dependency on proximity to the transducer, but we
> ultimately decided it would be easier to just increase pad size and not
> wash boards where we couldn't increase pad size, than pursue another
> large sample study. (We can turn the defect on and off, at a DPM level,
> on specific PCB layouts, by washing with ultrasonic and not washing with
> ultrasonic). Because of the pad size dependency, the low DPM
> occurrence, and design dependencies, I suspect all the "other" published
> studies would never find this failure mode.
>
> -Ryan
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
> Sent: Wednesday, August 03, 2005 6:39 AM
> To: [log in to unmask]
> Subject: Re: [TN] Question on cleaning boards with BGA.
>
> Hi Paul! What is the physics behind the ultrasonic cleaning system
> causing
> cracked BGA solder joints? Is your comment based on published data or
> internal data?
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
>
>
> Paul Edwards
> <paul@SURFACE-ART
> .COM>
> To
> Sent by: TechNet [log in to unmask]
> <[log in to unmask]>
> cc
>
>
> Subject
> 08/02/2005 09:41 Re: [TN] Question on cleaning
> PM boards with BGA.
>
>
> Please respond to
> TechNet E-Mail
> Forum
> <[log in to unmask]>
> ; Please respond
> to
> Paul Edwards
> <paul@SURFACE-ART
> .COM>
>
>
>
>
>
>
> Never use an ultrasonic cleaning system with BGAs unless you want to
> generate cracked solder joints...
>
> Assuming your ECN is at the former label location which is why you need
> complete adhesive removal... find out from your label supplier what type
> of adhesive they are using and have them suggest something...
>
> We use an alcohol/glycol/water mix to remove most label adhesives...
>
> Paul Edwards
> Surface Art Engineering
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of David Harman
> Sent: Tuesday, August 02, 2005 4:58 PM
> To: [log in to unmask]
> Subject: [TN] Question on cleaning boards with BGA.
>
> We are remanufacturing (reworking some of product) due to an ECR
> release. We apply a label with non-conductive adhesive that once
> removed leaves adhesive on the PCBA. This adhesive prevents the board
> from passing due to not making contact. The current process requires an
> operator to use IPA and a soft scrub to remove it. This process is time
> consuming. My CM has suggested that we ultrasonic the boards using S-10
> solvent.
>
>
>
> My boards have BGAs, interconnect pins, and switches along with the
> normal SMT parts. Will using this s-10 solvent in an ultrasonic cleaner
> work, and will it not cause any reliability issues with BGAs or other
> parts on the boards?
>
>
>
> Anyone have any other suggestions for auto cleaning my boards to remove
> the adhesive. We use the no clean process.
>
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