BGA for CO network or computer without underfill is OK (little or no
thermal shock and mech. Shock requirements). Fly is different story. I
would use underfill. Let me know if anything flying carrying people,
except NASA stuff, without underfill. I'll make sure avoid them next
time I am travel (not the TV set for entertainment...which I couldn't
care less... As long as they are not linked with cockpit power supply).
Arrows coming my way, I can see it... Need shield....just my 2 cents...
jk
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of
>[log in to unmask]
>Sent: Wednesday, February 05, 2003 8:52 PM
>To: [log in to unmask]
>Subject: Re: [TN] Single BGA ball rework
>
>
>Hi, Ted,
>
>Underfilling is historical and because we've conducted all our
>qualification tests on this product using it. It stems from
>the days when our first BGA-mounted cards were designed and
>built by a company in the States. The first time we put them
>near any (very mild) vibration, they failed miserably. I was
>new into this company then, when I was asked to take a look at
>why these boards failed, and it became obvious to me that the
>workmanship standard was terrible.
>
>I was also new to BGA's then (boy, have I learned a lot about
>them since!). I had a couple more cards assembled here in
>Singapore, working closely with the assembly house to ensure
>that the processes were as good as we could make them. I also
>came across underfilling as a means of supporting BGA ball
>contacts, especially for use in harsh environments. Whatever,
>I threw that process into the mix as well, as a sort of
>insurance policy. It pleased the bosses to think they had a
>good, visible solution to the problem, and certanly none of
>this model of board have failed since.
>
>Another reason I chose underfilling was to ensure that there
>could be no air/moisture/...contaminants (he says with bated
>breath) trapped underneath by the later conformal coating.
>
>Maybe next time we design or build a board with BGA's, we'll
>do away with the underflling process. I don't like it for many
>reasons - It's a manual process for us, potentially messy,
>certainly time consuming and involves more elevated
>temperature exposure for the board while we fill and then cure.
>
>Peter
>
>
>
>Ted Kong <[log in to unmask]> 06/02/2003 06:15 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
>
>
>
>
>
>
>
>
>Hi Peter,
>
>What make this BGA so unique that you have to use
>underfill? Also interest on what you have decided to
>do.
>
>Ted
>--- [log in to unmask] wrote:
>> 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 the
>> intended recipient, please delete it and notify us immediately; you
>> should not copy or use it for any purpose, nor disclose its
>> contents to any other
>> person. Thank you.]
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Technet Mail List provided as a free service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
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