9
\$\begingroup\$

I am involved in a project in which I need to create a few prototype boards that will use the AT91SAM9G20B-CU processor in the LFBGA217_J package.

Because this is a fine pitch BGA package, I'm not sure how to go about building prototypes that can be populated by hand. One thought I had was to have a PCB manufacturer create a simple "breakout" or adapter board that contains the BGA package and brings out the pins in some manner that will allow the board to be fairly easily soldered onto a main board that has the memory and I/O ports etc. Basically I'm trying to find a way to have a CPU board manufactured that converts the BGA package into a form that is more friendly to use in prototype boards.

I have the ability to solder fine pitch SMT packages with legs, but I can't deal with BGA's. I realize that once the prototype board is proven I can have the boards manufactured and assembled by a PCB fab house that can deal with BGA's, and that is what I eventually plan to do.

Currently I'm laying out my boards using Eagle CAD 6. Do you have any recommendations or advice for me?

\$\endgroup\$
9
\$\begingroup\$

From my experience, one-off assembly is extremely expensive in the US. Most places would not even bother giving me a quote for a single piece. Furthermore, you're likely to have the same problem with building a breakout board, since that will have to be assembled (it just displaces the problem). However, I have found that (with some work), it is possible to do BGA parts if you have access to a reflow oven, or if you have access to a fairly good heat-gun.

For heat gun instructions: http://devbisme.webfactional.com/blogs/devbisme/2012/08/24/mounting-bga-pcb-quickly-and-cheaply

For a reflow oven: I used #186 rosin flux at 295 C for 90 seconds with a 200 C preheat (180 seconds). This is higher than most manufacturers recommend, but the oven I have access to was donated to the University and is from the early 90s, so it doesn't actually get that hot. It was not necessary for me to use a stencil or even apply any solder paste, I simply coated the footprint area with flux and carefully aligned the package to the silkscreen.

One bit of layout advice if you do not have access to an oven is to make the board as small as possible. This makes it possible to heat up the entire board to a consistent temperature.

Also remember to tent vias under the BGA, if you do not, capillary action will cause the solder to flow from the balls into the vias, which is not what you want to do. http://siliconexposed.blogspot.com/2012/07/bga-process-notes.html

Finally, if you don't have access to x-ray inspection, make sure your silkscreen outline is precise. It should be slightly bigger than the package to assist you in aligning the part. You can print out the silkscreen layer in Eagle on a conventional laser printer with 1:1 scale to make sure you can align it on paper first.

\$\endgroup\$
3
\$\begingroup\$

A couple of things you might consider trying: 1. Sparkfun may still sell a toaster oven temperature controller. 2. Try an electric frypan... just don't tell your mum what you're going to do with it!

\$\endgroup\$
  • \$\begingroup\$ Thanks. I've decided to go ahead and just buy a proper re-flow oven. Seems I can get a decent small one for about $800. \$\endgroup\$ – Chimera Sep 20 '13 at 19:40
  • \$\begingroup\$ +1, and, don't use your mum's (or anyone else's) frypan if your using leaded solder! \$\endgroup\$ – bitsmack Jan 11 '16 at 18:51

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.