reball solder stencils - Page 1
Forum section: electronics / repair

author: pishta
author_rank: Contributor
timestamp: January 06, 2019, 11:57:19 pm
content: trying to reball a proprietary TI Dolby DTS chip and cannot find an appropriate stencil. Its a 17X17mm chip with a 16X16 pad matrix, 256 total pads with a 1.0 mm dot pitch (.050 ball). Do I have to use a generic 1.0 dot pitch stencil that is larger and just line up a portion of it? I also have an Analog Devices ADV7844 that has a smaller .075mm pitch, 23X23 pad (4 wide) with a nested 11x11 matrix. It also takes .050 balls. Am I going to have to hand place these balls under a microscope and toast them in the oven?https://www.eevblog.com/forum/repair/reball-solder-stencils/?action=dlattach;attach=615652;image

author: wraper
author_rank: Unknown
timestamp: January 07, 2019, 12:11:21 am
content: It's completely fine to use generic stencil. You can cover extra holes with adhesive tape. It should be heat resistant if you are going to reflow together with stencil. It's nice to have a jig around the stencil to avoid loosing solder balls. You can also place them manually but it's PITA.

author: pishta
author_rank: Contributor
timestamp: January 07, 2019, 12:26:24 am
content: Thanks! Would solder balls over no pads just ball up and roll off when I remove the stencil? would try and get them positioned first but a few may slip.

author: KE5FX
author_rank: Super Contributor
timestamp: January 07, 2019, 12:28:55 am
content: Dirty little secret: you don't really need a stencil for reballing one chip, just dump a lot of flux on it and touch each ball with a fine-tipped soldering iron, feeding a bit of solder to each. A good reflow profile will cover a mutitude of sins, including this one.

author: wraper
author_rank: Unknown
timestamp: January 07, 2019, 01:15:43 am
content: Quote from: KE5FX on January 07, 2019, 12:28:55 amIt's really "dirty" because result will be crap. A lot of flux will actually prevent from doing it well. You can somewhat do it but there is a lot of trickery to get a good amount of solder onto the pads to make balls of decent size.Quote from: pishta on January 07, 2019, 12:26:24 amThere is no harm in them. They just won't attach to IC.

author: wraper
author_rank: Unknown
timestamp: January 07, 2019, 01:18:22 am
content: Although I've rebelled even 0.4 mm pitch chips with just a soldering iron, it's an advanced level of masochism.

author: KE5FX
author_rank: Super Contributor
timestamp: January 07, 2019, 01:23:14 am
content: Quote from: wraper on January 07, 2019, 01:15:43 amI've found the flux is necessary for consistency, but to be fair that's likely to be a function of the quality and possibly the diameter of the solder being used. If you don't get good results with it, try it without it, and vice versa.Another approach is to add the 'balls' to the pads on the PCB rather than to the BGA itself.

author: wraper
author_rank: Unknown
timestamp: January 07, 2019, 01:24:33 am
content: Quote from: KE5FX on January 07, 2019, 01:19:03 amI did not say it cannot be done and read the post above. Usually most of the solder will either end up on the tip or ball up on end of solder wire. And big amount of flux only makes it worse. To get a decent job you would need a minimum amount of flux, very thin solder wire and iron tip which is mostly oxidized to not attract a lot of solder onto itself.

author: texaspyro
author_rank: Super Contributor
timestamp: January 07, 2019, 03:16:36 am
content: I usually use a stencil + solder paste to re-ball chips. Clean the chip with good wick/flux, stencil paste onto chip... leave stencil on the chip. Reflow paste with hot air. Remove the stencil. There is a youtube video by Paul Daniels that show how to do this (also some Louis Rossman videos).Using a fairly "dry" paste tends to work better than more liquid pastes.

author: pishta
author_rank: Contributor
timestamp: January 07, 2019, 03:27:45 am
content: Thanks all, Im set on using .050 balls because I cant imagine solder paste in the smaller holes. Just seems alot easier to roll a ball into a hole than to squeeging solder paste into metal pores, and to get a reliable solder ball size. The TI chip is most likely bad anyway (Onkyo A/V+recalled TI DSP chip receiver nightmare) so the replacement chip will most likely be pre balled. Its the HDMI switch chip that has the smaller pitch.

author: TheSteve
author_rank: Unknown
timestamp: January 07, 2019, 05:53:23 am
content: I've mounted the chip upside down and then lined up the stencil. The stencil gets a hinge on one end made of kapton tape. I then apply an even wipe of solder paste making sure the top of the stencil is clean. I then flip the stencil up leaving the small blobs of paste. A few seconds with hotair flows them into even balls.In this pic the paste has been applied and I'm ready to flip the stencil up.

author: PKTKS
author_rank: Super Contributor
timestamp: January 07, 2019, 10:53:46 am
content: Yes this is the way to go.I 've seen other folks creating stencils entirely on KAPTON tapeTedious thing but once done works as expectedPaul