lead free bga pads

Hi all

I'm having trouble finding pcb layout recomendations on the altera and xilinx web sites for lead free bga's. I'm wanting to use an altera F256 package and I can find all I need for the leaded version but nothing for the rohs packages. Does anyone know where I should be looking or what changes to the leaded footprints I should make?

all the best in 07

Colin

Reply to
colin
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I'm facing that issue right now for a FT256 package, and I'll do what I've done with all the other RoHS BGA parts I've had done leadfree (and that's quite a few) - use non-SMD pads with the recommended sizes from the leaded versions.

If my manufacturer thinks it needs to be tweaked - after all, they do a

*lot* of BGAs - they'll let me know.

So far I haven't had any problems provided I use a gold finish; of course, I haven't had sufficient time to get decent long term reliability data.

Cheers

PeteS

Reply to
PeteS

Thanks Pete, I will do the same.

Colin

Reply to
colin

Hi Vasile, Good link! As you say, I think the OP meant something else, but thanks for this! I'll add it to the RoHS BGA thread. Cheers, Syms.

Reply to
Symon

You're welcome.

As it happens, after re-evaluating the design, I am going to plonk down a 456 ball RoHS compliant BGA (and 2 256 parts plus some - 6 - at about

100 balls apiece), so I'll let you know how it all turns out.

Cheers

PeteS

Reply to
PeteS

Hi Pete, I read somewhere* that engineers used solder mask defined (SMD) pads for early BGAs because the parts were made of ceramic and could pull the pads off the board during vibration testing. With a SMD pad I guess the pad area can be larger to stop this. When lighter packages came along, the SMD pads were no longer needed, but folks carried on with SMD pads maybe because** "that's the way we've always done it". However, it turns out that SMD pads have a proclivity for microvoids*** at the pad/solder boundary. So, I wonder, now that Xilinx BGAs have metal heat spreaders built in, whether their mass has increased enough to make the SMD pad necessary once again. What do you think?

Cheers, Syms.

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Reply to
Symon

I've been bitten *very* hard from SMD pads on BGAs, especially fine pitch stuff. I've put down a lot of devices with heat spreaders on non-SMD and never had a failure due to reflow, but I've had a *lot* of failures (microvoids -> HiZ, and shorts pad to pad) using SMD whether they had heat spreaders or not.

Unless there is a compelling reason for SMD pads (some specialised manufacturers specify it and I *always* ask for the reason) I won't use them.

Cheers

PeteS

Reply to
PeteS

Hi Pete, Thanks for your comments. It more or less reflects my experiences, although I've not vibration tested an FPGA with heat-spreader design.

On a related subject, what do you think about via-in-pad. I've had great success with this, but recently people seem to be shying away from it.

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Near the bottom, Solving the Metric Pitch BGA & Micro BGA Dilemma

On page 30, the guy says that the voids are no problem, which backs up my experience. I wondered if you have a view on this?

Thanks, Syms.

Reply to
Symon

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