Hi, Dave,
Nothing at all - except that this BGA happens to be underfilled.
The debate, actually, is between my company (the customer) and a design
house. The design house maybe builds occasional circuits by hand, but
otherwise just farms assembly out via their customers or directly to local
assembly shops. The assembly shops here in Singapore normally build TV's or
Computer boards, and have no Class 3 experience or knowledge. The design
seems to have no manufacturing knowledge at all, though they like to think
they do just to save face when there's a problem to discuss.
Peter
"David Fish" <[log in to unmask]> 06/02/2003 05:24 AM
To: "TechNet E-Mail Forum." <[log in to unmask]>, DUNCAN Peter/Asst Prin Engr/ST
Aero/ST Group@ST Domain
cc:
Subject: Re: [TN] Single BGA ball rework
Peter,
Hand soldering seems very risky, because of:
* Potential to damage BGA balls and / or board.
* Inability to activate the flux used for rework.
Appreciating that your assembler may not want to reflow the board in
reworking the BGA, what prevents your assembler using a rework station that
uses hot air or IR energy to reflow the solder balls?
Dave Fish
----- Original Message -----
From: <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, February 04, 2003 11:57 PM
Subject: [TN] Single BGA ball rework
> Dear All,
>
> Thanks to everyone who responded to my last plea for information on
> adhesive for teflon. Tetra-etch is the obvious etchant - I must be
getting
> old not to have thought of it, though the bigger problem is actually to
> separate the still-bonded teflon from its flange in order to clean it up,
> re-etch it and bond it back again. Timing is everything though. and I was
> shown a memorandum yesterday, announcing that the OEM of the component is
> changing the teflon component material to GRP. So maybe we'll buy GRP
> replacement bits and bond them on instead of trying to recover the teflon
> mouldings.
>
> OK. Today's topic will either bring out amused smiles or cries of
outrage.
> One of our suppliers designs boards for us (functional, schematic diagram
> stuff only - though they do basic testing of built boards, once someone
> else has specified the layout design rules the PCB, done all the
> manufacturing stuff, etc.). One board is now failing, and they have
> diagnosed that one ball on the outside row of a BGA is no longer making
> contact with the board. Although only a prototype board, it is a Class 3
> type that could ultimately fly.
>
> For various reasons, the supplier is very reluctant to reflow the entire
> BGA or to replace it in order to solve the contact problem (the BGA is
very
> expensive). Instead, they came up with the idea of manually soldering the
> defective contact. [ I can now sense incredulous reactions from here!].
> They discussed their proposal with a local assembly house, who gave them
> the impression that the idea is possible to carry out (with suitable but
> unspecified equipment). Since then they have been insisting that they be
> allowed to repair the faulty BGA with this method. I used my power of
veto,
> strongly..
>
> I thought it might be a subject to put before learned council here,
though,
> in case anyone else has been thinking of trying this sort of repair. Has
> anyone out there come across any [successful] procedure for - or actually
> tried - manually 'touching up' a single BGA ball? If you have, is the
> procedure approved for anything, what is it approved for (board class,
> specific incidents/circumstances, etc), and where can I get a copy of it?
>
> The BGA in question is a large Xilinx XCV600E FPGA (Field Programmable
Grid
> Array, not a pin grid array), 40mm (1.6 inches) square with 5 rows of
balls
> and an open centre portion. The entire top body surface is covered with a
> metal plate. Soldered standoff height is about 20 mils.
>
> Have fun.
>
> Peter
>
> [This e-mail is confidential and may also be privileged. If you are not
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