Soldering WLCSP for prototypes by hand placement and reflow - Page 1
Forum section: electronics / projects

author: sacherjj
author_rank: Frequent Contributor
timestamp: November 29, 2012, 01:57:28 pm
content: I'm trying to figure out if it is even possible to solder a WLCSP prototype with microscope assisted hand placement and small reflow oven soldering. The specific chip I'm trying to test is FAB3103 (package info:http://www.fairchildsemi.com/dwg/UC/UC012AA.pdf)This is a 3x4 ball at 0.5mm pitch, and the whole device is 1.86mm x 1.44mm. I'm not sure how I'll place solder paste accurate enough.Is this anywhere close to possible? The chip is under a $1 at 10x quantity, so I'm willing to try a few takes to get it on there if needed. Just not sure if I can verify it is soldered without xray or similar. I guess testing resistances with test points or something may be possible.Anyone do something this small successfully?

author: robrenz
author_rank: Super Contributor
timestamp: November 29, 2012, 02:15:03 pm
content: Maybe tin the footprint with a tinned iron under the scope getting a nice dome of solder that forms from surface tension. This should make sure that no bridging can occur from excess solder. Clean and flux and place chip and reflow with a small tip hot air on backside of board so you don't blow it off while watching in the scope to make sure it seats and does not rotate. Or if you have a small hotplate do it on there while watching in the scope. Just thinking out loud, I have no experience with these.

author: nctnico
author_rank: Super Contributor
timestamp: November 29, 2012, 02:16:25 pm
content: Just tin the pads with braided copper (like soldering wick). Clean with alcohol, apply flux, position the chip and use a hot hair station from the other side of the PCB. I have succesfully replaced BGA memory chips this way. Because your chip is so small you may be able to apply the hot air from the component side but make sure to heat the surround PCB and not just the chip. The PCB needs most of the heat.BTW: some assembly houses have problems with soldering these packages. Because the chip is so light it doesn't push itself down enough but it also may have to do with the amount of solder paste.

author: sacherjj
author_rank: Frequent Contributor
timestamp: November 29, 2012, 02:33:24 pm
content: That is a good idea for pre-tinning the pads. I'm definitely getting the Amscope in before I try this. I'm wondering about doing a hot plate bottom to preheat the board to near melt temp (do tests to see what this setting is on another board and the time it takes to get there) then finish at the right time with hot air top.Great suggestions all, thanks.

author: robrenz
author_rank: Super Contributor
timestamp: November 29, 2012, 02:41:06 pm
content: I suggest spending the extra $19.00 for the trinocular head even if you dont think you will use it. My thread about ithere

author: sacherjj
author_rank: Frequent Contributor
timestamp: November 29, 2012, 03:23:55 pm
content: Quote from: robrenz on November 29, 2012, 02:41:06 pmYep. Already with you there. I'm looking at getting this model right now:http://store.amscope.com/sm-4tz-144a.htmlFrom what I'm reading, the Amscope cameras are just OK quality and we might want to source that somewhere else. But I agree that having the option is an easy choice to make.

author: nctnico
author_rank: Super Contributor
timestamp: November 29, 2012, 08:08:29 pm
content: A magnifier lamp will do just fine if you can't afford a Mantis... Either way there is not much to see on BGA packages.