Quick Question - BGA packages and pcb's

[monkeysolder]

Hello all- I am considering using a BGA packaged module for the first time and was wondering if any of you guys had any experience with making the pcb's for these. It is an 11x11 array with 2.5mm spacing. The other option for the module is a surface mount board-to-board connector, but it is slightly larger.

Would it be difficult to design and route the PCB using a 2 layer board (PCBexpress)? Only about 50% of the pins would be used, but it seems to me there could be issues with routing.

Is the manufacturing/reflow process unreliable or overly expensive for small qty (<100)?

Any other comments and suggestions are welcome.

Thanks,

 

[itsmoked]

Personally... I would avoid those stoopid BGAs like a dose of the clap... They instantly cause you assembly headaches.

But to the point, they aren't trivial but can be done. Generally you would want ground and power planes.
If this is a programmable part you want to assign the pins not let the compiler do it. You want to put all the pins you use on the outer two rows if possible. You will need 40mil vias.

Suggestion. Buy a BGA to pin socket adapter, solder in the socket, then you can just drop in the BGA no soldering and change it at will.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[monkeysolder]

Excellent advice. It is not programmable, so hopefully the original designer has put some thought into the layout... I will have to look more closely at the pinout. I will also look for the socket adapter, but size is the main reason for going twith the BGA package, so that may not work out for us. Thanks!

 

[itsmoked]

These people do it all and are very helpful. You might call them, I would.

http://www.1800adapter.com/

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[felixc]

To add my little penny to the general advice, unless a BGA provides tremendous advantages, go to other packages where you can inspect the solder.

If you have good volumes, this may be a different story.Still, your test procedure will need to have what it takes to properly determine if the part has a problem or not. JTAG is in many cases the best, if not the only way to test BGA-based designs.

2.5mm spacing between balls is quite generous, so manufacturing shouldn't be too difficult. The manufacturer might even have a pad size and trace layout guideline for its product. You said a 11 x 11 grid, but I guess that the center has no balls. How many rows of balls ar there? His will determine how difficult your layout will be.

 

[monkeysolder]

The center has balls too. This is not really a chip - it's a pcb with electronics with a BGA interface to save space. We are going to piggyback another board with either the BGA or board to board connector. Everything I have heard so far points me away from BGA though, so I will think about whether the small space savings is that important.

Thanks.

 

[MikeHalloran]

How you gonna reflow the balls without messing up the top of the little sub-board?



Mike Halloran
Pembroke Pines, FL, USA

 

[itsmoked]

A small space savings is NOT worth it... Unless the product cannot work at all without saving the space.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[logbook]

I hate BGS's big time. Routing is a misery even on 4 or 6 layer boards. Soldering is a nightmare and needs to be done by specialist assembly houses. There is no mechanical compliance like you get on a nice gull wing package. I specifically limited myself to a 12K logic element Altera since the bigger ones use BGA packages. On small production runs you will be hard pushed to get the reliability. Once the volume is higher they can get used to making it and improve the quality, but without XRay inspection of the soldering you don't know how close to the edge you are working.