Hand BGA soldering and more - Page 1
Forum section: electronics / projects

author: blueskull
author_rank: Unknown
timestamp: November 01, 2015, 08:42:06 am
content: I just found this video, made by Colin, the chip whisperer guy. I think it might worth taken a look at.

author: crispy_tofu
author_rank: Super Contributor
timestamp: November 01, 2015, 09:14:42 am
content: Fantastic, thanks for sharing!I loved the uncertainty at 14:57 when he was lowering the QFP...

author: TheRevva
author_rank: Regular Contributor
timestamp: November 01, 2015, 11:43:05 am
content: Quote from: crispy_tofu on November 01, 2015, 09:14:42 amYep, I loved it too... (I'm guessing it boils down to an issue of 'self-confidence'?)When I was l was looking at 27:08 where he was checking the registration of the QFP thru the scope I saw the shorts on the chip beside U15 & C45 and then I noticed he'd already made some overlay comments on the video.I'm a total novice @ SMD and yet my first SMD 'project' involves a similar 144pin QFP (Atmel AT91SAM3X8E) along with a whole bunch of 0402 passives. Have pity on me!

author: John_ITIC
author_rank: Frequent Contributor
timestamp: November 01, 2015, 10:04:27 pm
content: It would be very interesting to know what the pitch and ball size was on that BGA. He blundered around a fair bit when placing that BGA so I would not be surprised if there were solder ball shorts underneath. I found myself only putting solder paste on non-BGA parts. Once all parts were hand-placed, I simply used tacky flux on the BGA balls, aligned the BGAs manually and then reflowed the whole board. This minimizes the risk of solder shorts under the BGA. The down-side is that if the BGA balls are not properly aligned vertically (i.e. different size after reballing) it is possible to have bad solder joints due to less than ideal wetting. I would love to get my hands on a reasonably priced Xray machine to be able to verify a proper reflow under BGAs. Currently, I use an inspection mirror and stereo microscope to inspect for proper ball collapse on the outer ring of balls but there's no way to check for shorts or bad solder joints on inner balls.

author: mrpackethead
author_rank: Super Contributor
timestamp: November 01, 2015, 10:13:50 pm
content: Quote from: John_ITIC on November 01, 2015, 10:04:27 pmunless you have xray inspection.. but thats not so common in the average workshop.

author: marshallh
author_rank: Unknown
timestamp: November 02, 2015, 03:18:40 am
content: Some notesDon't mix leaded and leadfree - BGAs come preballed generally with leadfree unless you specifically order otherwise (usually at great expense)I prefer assembling BGA with paste instead of just flux. I have had a couple failures with just flux, but no failures with paste.Even if you flub the placement and have to nudge it around some, it will still work. Even for QFPs. However depending on how much you smeared there will be some leftover beaded up solder that will cake into place after reflow. This is safe but can still be cleaned off with ultrasonic wash.I usually grab small bgas with my smd curved tweezers. Bigger chips that are too heavy I just use my fingers and drop it on like a dorito.To get good, crisp paste deposition the key is to only squeegee that area ONCE. If you go back over it any more it will force paste through the apertures and smear. It'll still solder fine but may have harmless beaded up solder balls afterwards.See the link in my sig for more notes - it's the same one Colin used.I have done dozens of bgas now and had no problems after the first 2 several years ago.Below, all hand assembled and 100% working down to 0.8mm pitch.