Michael,
Dr. Johnson also identified a rotary brush prep process of reworked
underfilled BGA/CSP sites that also improved the Mech Shock survivability
even more. Probably due to roughing up of the solder mask which improved
underfill adhesion.
Bruce Misner
> ----------
> From: WEEKES, MICHAEL HS-SNS[SMTP:[log in to unmask]]
> Reply To: TechNet E-Mail Forum.;WEEKES, MICHAEL HS-SNS
> Sent: Wednesday, May 15, 2002 10:35 AM
> To: [log in to unmask]
> Subject: Re: [TN] BGA's on ruggedized assemblies...
>
> Is underfill really reworkable - I know rework may be feasible, but let's
> be
> honest about the detrimental effects of the thermal effect and
> contamination
> of a site where underfill was applied, cured, heated and
> mechanically/chemically removed. I welcome comment - our assemblies are
> too
> expensive to scrap out. Any personal experience with any loctite or other
> "reworkable" undefilled - I rank "reworkable" up there with "washable, but
> not soluble".
>
> -----Original Message-----
> From: [log in to unmask] [mailto:[log in to unmask]]
> Sent: Tuesday, May 14, 2002 8:01 PM
> To: [log in to unmask]
> Subject: Re: [TN] BGA's on ruggedized assemblies...
>
>
> Our Rockwell friends, through the fumes of Mountain Dew and Coke, will say
> "No" if your attachment processes are good enough. Personally, though,
> after some early (low level) vibration failures with some third party
> designed and assembled boards, I built some more to my own spec and
> introduced underfilling as an insurance policy. I hope to be able to
> vibration qual test boards with and without underfilling to see if this
> process is really necessary.
>
> To answer your question, it depends .... on your processes, the operating
> conditions and expected life of the product, and maybe even the board and
> BGA materials. Underfill manufacturers claim that using underfill can
> improve the fatigue life of BGA solder joints by a factor between 3 and 5,
> but it is another process and it involves heating boards an extra time (if
> you use the capillary action type underfill) to carry out the underfill
> process and cure the material. The no-flow type is applied and cured
> concurrently with the assembly of the BGA onto the board and doesn't
> involve the extra thermal excursion.
>
> I recommend you try qualifying boards with underfill and without it to see
> if you need the extra process. Underfilling is not necessary in all
> situations, nor a recommendation, but it won't do any harm either if you
> want to use it anyway.
>
> Peter
>
>
>
> [log in to unmask] 15/05/2002 05:08 AM
> Sent by: TechNet <[log in to unmask]>
>
> Please respond to "TechNet E-Mail Forum."; Please respond to SteveZeva
>
> To: [log in to unmask]
> cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
> Subject: [TN] BGA's on ruggedized assemblies...
>
>
>
>
>
>
>
>
> Hi All!
>
> Gotta question, when BGA's are used on ruggedized assemblies (at least
> Level-4, probably Level-5), is underfilling BGA's recommended, or a
> necessity?
>
> Thanks, as always...
>
> -Steve Gregory-
>
>
>
> [This e-mail is confidential and may also be privileged. If you are not
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> intended recipient, please delete it and notify us immediately; you should
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>
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