XCore Exchange

I would like to design a board for the XS1-G4 144 BGA package. What pad diameter should I use? How much clearance should I give between the solder mask and pad?

The datasheet says the maximum ball diameter is .4, but there is no dimension for the BGA pad size. Pitch is .8

Here's a good document on PCB design using BGAs:

http://www.altera.com/literature/an/an114.pdf

You can copy the dimensions used on the XMOS boards, by looking at the files with a Gerber viewer. It's a good idea to check with the company that will be assembling your board, as well. That's especially important when it comes to solder-mask defined vs. non solder-mask defined pads. NSMD seems to be preferred.

I tried downloading the design files, but I haven no idea what file type that is. Where can I get gerbers?

Look for pcb_XC-1_1-0_7.zip on the XMOS web site. I downloaded it some time ago and it has the Gerbers in it. I was able to import them into the Pulsonix PCB software I use. I just checked the Gerbers with GC-Prevue; the BGA pads are 0.45 mm diameter and the vias are 0.5 mm diameter, with a 0.127 mm drill.

Ok. I had seen those, those just were not the types of gerbers I have seen before.

So the BGA size for the 512 package is a bit bigger, with a .5mm ball diameter vs the .4 of the 144 BGA.

Do you think I will be fine with a .35mm diameter pad and a .55mm diameter mask clearance?

That pad seems too small.

The maximum ball size for the 144 BGA is .4mm, is .35mm really too small? It seems consistant with the .45 and .5mm for the 512 BGA.

It's usually recommended that the pad diameter is the same as the ball size, for optimum reliability.

From what I read, you want the pad the same as the BGA pad, not ball. If the pad is too big (i.e. the max ball diameter) than the solder will pull away from the BGA. Too small and the opposite happens.