EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: extraextra on March 26, 2018, 09:25:10 pm
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I have a board with a fried DFN chip and I'd like to replace it. It's a MOSFET in a DFN package and all of the pads are underneath it. This is the chip: http://www.ubiq-semi.com/en-article-upi-663-1875 (http://www.ubiq-semi.com/en-article-upi-663-1875)
I've never done work on SMD components much less DFN and I'm not 100% sure where to start. I know I'll need a heat gun and tweezers for sure, and I saw somewhere that I can use foil to prevent me from blowing away the surrounding components, along with a note sheet recording what components were where so when I do accidentally blow them away I can put 'em back. What else do I need to have on hand? Flux, solder paste, some applicator(s), luck?
I searched around and found a lot of information on what is required for general SMD rework -- what I saw (including the EEVBlog videos) made sense but it all relies on having access to the pins (or at least it seems to).
Related: Is there a video by Dave about this specific subject? I couldn't find one with the term "DFN" in it. There's this video (QFN, close enough): https://www.youtube.com/watch?v=M_rO6oPVsws (https://www.youtube.com/watch?v=M_rO6oPVsws) but it demonstrates a way to install the chip with visible pads.
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I do this kind of stuff by lightly pre-tinning both PCB pads and chip pads. Very lightly. Then put some flux and roughly position the chip. Apply heat. No need to cover anything, unless you have some plastic components nearby. If your air blows away surrounding components, you've got too much air, it will also blow away the chip you are trying to solder. Once solder is molten, poke the component slightly on the side, it should return to is right place with surface tension of the solder.
Look at Louis Rossmann channel, he soldered plenty of chips with invisible pads.
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Thank you, that makes sense. Solder paste and flux it is!
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You don't even need solder paste. The combined amount of solder on the pads and the board after pre-tinning should be sufficient for reflow.
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for this puppy i use paste solder and hakko hot air station, the center pad is sometime used as dissipation surface
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Check out some of Luis Rossmann's Macbook repairs on Youtube, plenty of QFN chip replacements to be seen (same style of package, but with pads on all four sides, hence the "Q" for quad, as opposed to "D" for dual).
Hot air, flux and solder (no paste required) :-+