Measure the size of the pad on the underside of the BGA device.
The size of the pad on the PWB should be about the same size to make the
joint of equal strength at both interfaces.
0.25 for a 0.60mm dia ball sounds far too small to me.
Agreed though that you may still get failure at depanelisation due to
board flexure. Best to avoid that.
Regards,
Ken Bloomquist wrote:
> Yep CAB Maestro 3, http://www.cabtechn.com/maestro3-support.html . We have
> one and it works great!
>
> KennyB
> -----Original Message-----
> From: Mike Sewell [mailto:[log in to unmask]]
> Sent: Friday, July 18, 2008 1:19 PM
> To: [log in to unmask]
> Subject: Re: [TN] Mechanical damage to BGA
>
> I've got the same problem on our FKN with thin boards. At a previous place
> we had a Cab(?) Maestro manual depanelizer that did well on .030" boards.
> The board didn't move into the wheels, you placed the V-score onto a guide
> then pulled the pizza wheel over the score.
>
> Mike
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of McGee, Michael
> Sent: Friday, July 18, 2008 3:13 PM
> To: [log in to unmask]
> Subject: Re: [TN] Mechanical damage to BGA
>
> How thick is the remaining web of material? Can you get away with 7mils (1/3
> the material) or less. Then you should be able to adjust the gap between
> wheels in your FKN to ride in the slot.
> I've seen the problem where there is insufficient groove depth to hold the
> wheel on track. It gets a little messy.
>
> -Mike
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
> Sent: Friday, July 18, 2008 2:56 PM
> To: [log in to unmask]
> Subject: Re: [TN] Mechanical damage to BGA
>
> Well Mike,
>
> The issue is the thickness of the board. I have tried to use our FKN
> depanelizer only to realize that the blades don't really guide into the
> groove. So I've somehow managed to actually cut into the PCB...
>
> Actually this was supposed to be my other question: how can one depanelize a
> V-grooved 21mils thick board?
>
> Thanks,
>
> Ioan
>
> -----Message d'origine-----
> De : McGee, Michael [mailto:[log in to unmask]]
> Envoyé : July 18, 2008 3:28 PM
> À : TechNet E-Mail Forum; Ioan Tempea
> Objet : RE: [TN] Mechanical damage to BGA
>
> Ian,
> I would never dream of manually cracking a v-groove panel with SMT
> parts. Get a "pizza slicer" style depaneler. They can be had relatively
> cheap and work great. They put zero stress on the board. Even an
> inexpensive manual one is faster and more ergonomic than manually
> breaking them.
>
> -Mike
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
> Sent: Friday, July 18, 2008 1:48 PM
> To: [log in to unmask]
> Subject: [TN] Mechanical damage to BGA
>
> Dear Technos,
>
>
>
> I have this BGA that gives me a headache. In many instances the boards
> do not pass test, we press on the BGA and they start working; a
> classic... The problem solder joints are always on the same side of the
> component and on the outer row; needless to say, we have a V-groove line
> that is manually cracked. So the cause is most likely mechanical stress
> that causes the pads to detach from the PCB. After prying off some BGAs
> we see the soldering is good, all the pads come off the board and stay
> solidly attached to the balls.
>
>
>
> The specifics of this board are a bit special and I would need your
> opinion on what to improve in the design in order to eliminate the
> propensity to damage.
>
>
>
> PCB is 18.55x28.65mm, FR4, 0.55mm [0.021"] thick
>
> The BGA is 17x17mm, 1mm pitch, 0.65mm balls assembled on 0.25mm circular
> pads. In the troubled zone the pads are connected to 0.050mm traces.
>
>
>
> My opinion is that the board flexes very easily and even if we fix the
> depanelization (I will modify the panel) all the subsequent handling,
> including the integration of this module, puts the joints at high risk.
>
>
>
> I think the pads are too small so they do not have sufficient adhesive
> force to stay put on the PCB. On top of it, the traces are so minute, so
> the slightest stress will be destructive.
>
>
>
> Would increasing the pad size help? Is this construction (thin PCB +
> superfine traces) viable?
>
>
>
> Could the CTE mismatch be strong enough to cause the damage, instead of
> the mechanical stress from bending the board?
>
>
>
> Thank you,
>
>
>
> Ioan
>
>
>
>
>
>
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--
Eric Christison Msc
Mechanical Engineer
Consumer & Micro group
Imaging Division
STMicroelectronics (R&D) Ltd
33 Pinkhill
Edinburgh EH12 7BF
United Kingdom
Tel: +44 (0)131 336 6165
Fax: + 44 (0)131 336 6001
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