Using vias for BGA lands - Page 1
Forum section: electronics / projects

author: Skimask
author_rank: Super Contributor
timestamp: April 21, 2014, 07:39:52 am
content: Order a few LTM8045 to play around with, 40 pin BGA package, 10x4 array, .050" spacing on the balls.Originally used the LM2588, worked good, just too much PCB space to get my +/- 12v out of the 4cell NiMH pack.Thinking I can use a couple of these and get it down to a couple sq.inches.The billion dollar question.....Do I dare try and use an array of vias for the BGA lands?I've got a hot plate and hot air gun for reflow, and an semi-untested reflow oven that I just finished up a few weeks ago. Along with that, I've got plenty of experience with SMDs. No X-ray machine...yet...

author: Psi
author_rank: Super Contributor
timestamp: April 21, 2014, 10:14:50 am
content: i'd probably give it a try, if it was me.Maybe pre-fill all the vias with solder and then wick them flat, so the balls dont all melt away through empty via holes during reflow.

author: Skimask
author_rank: Super Contributor
timestamp: April 21, 2014, 12:02:48 pm
content: I was just about to make a smartass reply...something to the effect of my balls melting away...but before I made a complete ass of myself, I looked it up...then I beat myself.I had always thought that the balls that defined a BGA were real, solid chunks of metal...not actual big 'solder balls'. Pre-filling the vias/lands makes much more sense now.I was only thinking of using the vias to help transfer heat from the hot plate. Considering the LTM8045 runs roughly ~$15USD for each one, you probably just saved me $30 on my first attempt.

author: Psi
author_rank: Super Contributor
timestamp: April 21, 2014, 12:28:15 pm
content: Ive never actually reflowed a BGA before, so maybe wait for someone else to confirm it will actually work.

author: Jeroen3
author_rank: Super Contributor
timestamp: April 21, 2014, 12:48:15 pm
content: You only need 1 untented via for the RUN pin, all other pins can be done using normal traces since the bga has large groups of pads.But maybe you can already route one small signal wire between two reduced size bga pads. Take a look at your pcb manufacturers details.

author: amyk
author_rank: Super Contributor
timestamp: April 21, 2014, 01:00:02 pm
content: Quote from: Skimask on April 21, 2014, 12:02:48 pmYouTube "reballing" and watch a few videos...

author: PA0PBZ
author_rank: Super Contributor
timestamp: April 21, 2014, 01:00:18 pm
content: Quote from: Jeroen3 on April 21, 2014, 12:48:15 pmAssuming that you want to connect RUN to Vin you really don't need anything fancy at all.

author: Skimask
author_rank: Super Contributor
timestamp: April 21, 2014, 01:32:17 pm
content: Quote from: amyk on April 21, 2014, 01:00:02 pmHoly crap! Can I get a reballing video without stupid background music?Good idea watching a handful of videos though. This BGA40 should be a piece of cake, but I don't think I want to try my hand at any GPUs anytime soon.

author: Skimask
author_rank: Super Contributor
timestamp: April 21, 2014, 01:36:07 pm
content: Quote from: PA0PBZ on April 21, 2014, 01:00:18 pmAccording to LTSpice, the run pin only pulls ~203uA using the reference and not much different under other conditions. I'm kinda wanting to breakout everything and that being the case, a tiny trace should do just fine.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 21, 2014, 01:52:00 pm
content: What are you placing this on, a board with 1, 2, 4 or more layers? Looks like it can even be done single-layer with 8/8 design rules, nothing very challenging (not that I'd recommend a single layer build, of course). Two layer should be quite sufficient, with ground plane underneath, vias and bypass caps as suggested in the datasheet.Tim

author: Skimask
author_rank: Super Contributor
timestamp: April 21, 2014, 02:10:38 pm
content: Nope, just planning on double layer board. Doesn't look too difficult, just never designed a board for a BGA before from scratch.Plan on practically copying the datasheet (Fig's 2&3) as far as parts placement goes except I think I'm going to go the route of the demo board (DC1533A) and put 'cuts' in the pours around the V+ & V- outputs so I can change up the board as needed. Or maybe make the top of the board for boost and bottom for inverting, one or the other (but not both!). Haven't decided yet, or figured out if that's possible.