I'd have to concur with most of the discussion, X-ray is a waste of time
and money and is an un-necessary comfort zone. It does come down to
process control and I might add good design. There is an interesting
article in either SMI 96 or 97 on Optimal BGA land pattern design. The
reflow profile is the most critical in the process, a coleague of mine
had a run of reject product and found that the profile had changed.
Prior to that yields in the 99+.
Another area to watch out for is shelf life of boards, especially Au/Ni.
Freshly supplied boards that are chewed up quickly resulted in high
yields. Boards that sat around for a couple of months did not fair so
well.
As Paul mentioned, depanneling is important, or the method rather. We
had a mechanical break out tool that that separated the panels which was
rather violent. I also observed that some people were also breaking
boards by hand. I tried a small experiment where by initialising the
boards prior to depanneling and achieved a yield figure. I then
depanneled the boards with the mechanical breakout tool and found the
yield dropped by 7%. Since then we used a Depanelling tool that is a
board separator using a blade that runs along the V-Groove. No drop in
yields from pre to post breakout testing.
Regards
Zoran Raich
> ----------
> From: Paul Klasek[SMTP:[log in to unmask]]
> Sent: Monday, August 03, 1998 5:14 PM
> To: [log in to unmask]
> Subject: Re: [TN] Glenbrook x-ray??
>
> It's fine Dave ; you definitely did not leave THAT impression ; that
> was
> the beaut .
> True; we have it "easier" here ; without validated process or change
> we
> can not even pull button on P&P .
> But with the "inspection" with XR for enviro life ; yes the amount of
> solder visible would make me feel good ; but the invisibilities of
> joint
> quality would not make it quite that comfortable , especially for
> demanding environments .
> One of our fellows here used to make modem cards on FR4 laminate and
> uttered one day a remark (not a polite one) on the reject ratio trap
> he
> set on his subjects ( tested cards prior to depaneling with a top
> 99.xx
> yield , and no prizes for guessing he did not get that AFTER
> depaneling
> ! [-7%!]) . Fixed by redesigning and resequencing the process .
> I personally think the shorts are in the past and not reliability
> relevant (apart from "rework" damages) ; opens are the issue nowadays
> .
> Not much to do for XR .
>
> Paul Klasek
> http://www.resmed.com
> > ----------
> > From: David D
> Hillman[SMTP:[log in to unmask]]
> > Sent: Saturday, 1 August 1998 4:10
> > To: [log in to unmask]
> > Subject: Re: [TN] Glenbrook x-ray??
> >
> > Hi TechNet - Your right Steve/Paul, it is not necessary to xray and
> > test
> > every BGA on every assembly (I didn't mean to leave that
> impression).
> > A
> > reasonable sampling in plan in conjunction with good process control
> > as
> > outlined in JSTD-001 allows for low process cycle time and
> reasonable
> > costs. I have seen some examples of where several assembly houses
> have
> > a
> > good handle on the placement gauge R&R, inspect their solder paste
> > print
> > and have tuned in their reflow profile - they do only sample
> > electrical
> > testing, no xray and are producing quality product. I think the
> amount
> > of
> > "inspection" is also part of an assemblers comfort level for the use
> > environment their product has to live in.
> >
> > Dave Hillman
> > Rockwell Collins
> > [log in to unmask]
> >
> >
> >
> >
> >
> > "Stephen R. Gregory" <[log in to unmask]> on 07/30/98 06:48:32 PM
> >
> > Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please
> > respond
> > to [log in to unmask]
> >
> > To: [log in to unmask]
> > cc:
> > Subject: Re: [TN] Glenbrook x-ray??
> >
> >
> >
> >
> > In a message dated 98-07-30 19:14:35 EDT, you write:
> >
> > [log in to unmask] (Paul Klasek)
> > To: [log in to unmask]
> >
> > I concur with David ; have been watching this discussion for some
> > time
> > and kept out as I thought perhaps I'm the odd one out in extreme as
> > usual ; but since Dave cracked the pot the way it is :
> > If the process is out of window to such a degree this kind of
> > machinery
> > is needed ; I'd say $ much better spend would be in the process
> gear
> > ; not
> > inspection gear . >>
> >
> > Hey there Paul!
> >
> > Well since you and Dave started this, I'm gonna jump on the
> bandwagon
> > too.
> > I
> > asked the question that I'm about to ask on another web forum a
> while
> > back,
> > and the reponses were kind of guarded...(it was like they didn't
> want
> > anybody
> > to see them answer with what some may percieve the wrong response).
> > But my
> > question was; why does it seem that if you want to do BGA, the
> > consensus is
> > you need to have xray capability?
> >
> > I know that xray is a tool that will allow you to see things that
> you
> > normally
> > can't see, but is it REALLY necessary? It would seem to me that if
> you
> > can
> > make sure that you lay enough paste down, put the part where it's
> > supposed
> > to
> > go, and got your oven cranked-up with enough heat, you're in the BGA
> > business...and you can do all that stuff without an xray machine.
> >
> > "But you can't see the solder joints dross-breath, that's why you
> need
> > an
> > xray
> > machine.." some may say. But I didn't see everybody getting
> spooled-up
> > about
> > having xray when we started putting decoupling capacitors beneath
> DRAM
> > years
> > ago...can't see those solder joints either. So, is it really
> > necessary?
> >
> > -Steve Gregory-
> >
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