[Coco] assembly questions?

[jdaggett at gate.net]

Kevin

What is nice about PC motherboards are that they are often not 
dropped from belt hiegth or from the top of a desk. You ought to see 
how much the PCB of a cellphone or a pager(beeper)  flexes during 
a 4 foot drop onto tile floor. A lot has to do as to where the supports 
are and how stiff the area is where the BGA part is located. In one 
product I worked one there were two 256Kx8 SRAM  in fine pitch 
BGA. Two joints on only one of the two rams would break during 
drop testing. The other SRAM device  never had a problem It was 
all location. The one that had problem was located the fartherest 
from any su pport and in a drop that section of the board would flex 
at least a quarter of an inch. 

Large BGA parts are offer some stiffing to the board, especially 
when a heat sink is placed on it. Alters the vibration frequencies 
when dropped or during board flexures. 

I have a good experience in this area. 

james




On 26 Jul 2004 at 21:18, Kevin Diggs wrote:

Date sent:      	Mon, 26 Jul 2004 21:18:14 -0700
From:           	Kevin Diggs <kevdig at hypersurf.com>
To:             	CoCoList for Color Computer Enthusiasts 
<coco at maltedmedia.com>
Subject:        	Re: [Coco] assembly questions?
Send reply to:  	CoCoList for Color Computer Enthusiasts 
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> Hi,
> 
>  These BGA things sound scary. The old 386 I have mentioned
> before ... the one that is 13+ years old ... the one that has had a
> glass of cranberry juice spilled on it ... and had mice pee on it ...
> Still works. Makes me wonder how long my much newer Intel D815 (p3)
> and D845 (p4) motherboards are gonna last?
> 
>      kevin
> 
> jdaggett at gate.net wrote:
> > 
> > Mark
> > 
> > The biggest problem with BGA is when the BGA pads on the PCB
> > themselves. I have sliced and dice enough PCBs with BGA joint
> > and looked at joints under a scanning electron microscope to know
> > about how any BGA joint can fracture.
> > 
> > The BGA pads need to be protected at all stages after initial etch.
> > In the line of work that I used to do, 90% of the failures were at
> > the PCB/Ball joint. Often due contaminations from the PCB processing
> > that even presolder cleaning will not correct. Often what happens is
> > when a weakened joint is exposed to high stress and board flexure,
> > there is an icreased risk of failure.
> > 
> > Simply this, if you solder to copper chloride the joint is going to
> > fail. Almost invariably the contaminat is chlorine.
> > 
> > james
> > 
> > james
> > On 26 Jul 2004 at 15:57, mmarlett at isd.net wrote:
> > 
> > From:                   mmarlett at isd.net
> > To:                     coco at maltedmedia.com
> > Date sent:              Mon, 26 Jul 2004 15:57:08 -0500
> > Subject:                RE: [Coco] assembly questions?
> > Send reply to:          mmarlett at isd.net,
> >         CoCoList for Color Computer Enthusiasts
> > <coco at maltedmedia.com>
> >         <mailto:coco-
> > request at maltedmedia.com?subject=unsubscribe>
> >         <mailto:coco-
> > request at maltedmedia.com?subject=subscribe>
> > 
> > > David,
> > >
> > > We have no internal Xray, all done at the vendor. The thing you
> > > have to watch out for is that when the boards are assembled they
> > > are clean, parts are clean. Thus you have contact, poor, but
> > > contact. So you functionally test and the board passes. As
> > > oxidation occurs you now start to have problems in the field, the
> > > worst kind to have, $$$$$$.
> > >
> > > We are all new to this and haven't had alot of rework on the BGA
> > > side. Our rework station will do just about anything. Get the
> > > correct nozzle and you are set.
> > >
> > > Mark
> > > Cloud-9
> > >
> > > >Ya, we've been looking at getting it for my work to repair our
> > > >new boards which would be BGA.
> > > >
> > > >The actual board stuffing takes place at our board house vendor. 
> > > >As far as X-Ray analysis, we're just planning on doing a
> > > >functional burn-in test to make sure they work instead.
> > > >
> > > >You probably have to go thru all that for mil-spec stuff which
> > > >can add greatly to the cost of the board over just getting the
> > > >board stuffed.
> > > >
> > > >
> > > >Dave
> > > >
> > > >-----Original Message-----
> > > >From: coco-bounces at maltedmedia.com
> > > >[mailto:coco-bounces at maltedmedia.com] On Behalf Of
> > > >mmarlett at isd.net Sent: Monday, July 26, 2004 3:16 PM To:
> > > >coco at maltedmedia.com Subject: RE: [Coco] assembly questions?
> > > >
> > > >Dave,
> > > >
> > > >$12k, that is a bargin. Ours is $85K. Not Cloud-9's either, this
> > > >is a hobby for me. That would be my REAL job's machine.
> > > >
> > > >Regards,
> > > >
> > > >Mark
> > > >Cloud-9
> > > >
> > > >>BGAs really need to be set on a board by machine.
> > > >>
> > > >>Normally both sides of the board are heated for a predetermined
> > > >>time and/or temperature when the chip is set.
> > > >>
> > > >>You can see what a small BGA rework station looks like at
> > > >>coopertools.com
> > > >>
> > > >>The Weller one is real nice for small scale stuff, and it's a
> > > >>bargain
> > > >at
> > > >>12 grand!  ;)
> > > >>
> > > >>
> > > >>Dave
> > > >>
> > > >>-----Original Message-----
> > > >>From: coco-bounces at maltedmedia.com
> > > >[mailto:coco-bounces at maltedmedia.com]
> > > >>On Behalf Of Kevin Diggs
> > > >>Sent: Monday, July 26, 2004 2:28 PM
> > > >>To: CoCoList for Color Computer Enthusiasts
> > > >>Subject: Re: [Coco] assembly questions?
> > > >>
> > > >>Hi,
> > > >>
> > > >>    Regarding previous discussions on this thread, Is there
> > > >>no way to use these new packages (BGA) with some kind of
> > > >>adapter on older circuit boards that hobbyists can make?
> > > >>
> > > >>                                   kevin
> > > >>
> 
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