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These small LGA16 parts needed replacing:

enter image description here

Desoldered them with heat gun, cleaned with acetone, put new parts into place, fixed them with this sticky aluminum tape, applied flux and put them to the oven:

enter image description here

upped the temperature a bit on the soaking part of the profile and baked them. They all came out bad (brand new parts used). Tried doing them manually with the heat gun as usual in an attempt to fix any non contacting pads without any luck.

What would the main culprit be here, upping the temp a bit from a 204 deg C max to 212 max, with the max reached some 10-15 seconds faster, or that aluminum foil ?

------------------EDIT-----------------

In response to the comments - I should have mentioned that all else besides the two changes are my standard procedures / tools that I have been using, mostly successfully. A third culprit comes to mind: the bag with parts got unsealed some 30 hours before I did the work. I did not left it open but neither did I reseal it. The humidity indicators inside looked fine after those 30h, parts being of MSL 3.

--------------------EDIT2----------------

What do you mean by "they all came out bad"? – Justin 20 hours ago

Actually, this particular batch of 5 do not respond on I2C. Usually when they turn bad it means their sensing capability is diminished

--------------------EDIT3----------------

After many more hours of frustration I have (likely) discovered some more subtleties of reworking; have not used the oven but just the hot air gun

It seems when I only do 185 - 190 deg C just so the solder melts I am getting opens like @Chris Stratton suggested As soon as I go 200+ no mor eopens, but the sensitivity is badly impacted... I am, how should I say, in despair...

kellogs
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    I'm hardly an expert on the topic, but is cleaning with acetone such a good idea? See this: https://electronics.stackexchange.com/questions/317859/is-acetone-or-isopropyl-alcohol-better-for-removing-rosin-flux Why aren't you using isopropyl? – Lundin Nov 04 '20 at 12:22
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    You should be using a "hot air tool" not a heat gun. You want to heat the specific part *and watch what happens* not put the entire board in an oven. – Chris Stratton Nov 04 '20 at 13:34
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    Did you use only flux or solder paste with flux? For modern boards using lead free solder, 212C won't be enough to melt the existing solder. – user1850479 Nov 04 '20 at 14:15
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    What do you mean by "they all came out bad"? – Justin Nov 04 '20 at 15:23
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    So the soldering looks good? Does it have a ground pad underneath? On some parts, you can measure if the ground pad is disconnected using an ohmmeter to a tiny metal bit of the leadframe that sticks out of the package at the corners. – Justin Nov 04 '20 at 15:55
  • @Justin soldering is fine, no ground pad – kellogs Nov 04 '20 at 15:58
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    Maybe try soldering them with just a soldering iron on the pads one by one after preheating the board a bit. It might result in less heating internally. – Justin Nov 04 '20 at 16:01
  • @Justin i actually tried that at another person's suggestion a week ago, no chance! I ain't that skilled... Anyway, both the oven and the heat gun (or hot air gun, I did not know they were separate tools) methods are more or less fine. Never did I have 5 out of 5 boards come out with the MEMS fried like it happened yesterday. – kellogs Nov 04 '20 at 16:05
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    So your normal method usually works for these same parts, and your modified method with 2 changes doesn't work? Can't you go back to the original method? – Justin Nov 04 '20 at 16:10
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    Get yourself a 10x eye loupe and carefully inspect where the solder fillet meets the chip all around. It's far more likely that you have simple opens than damage to the ICs. – Chris Stratton Nov 05 '20 at 17:47
  • Why would you leave the aluminum tape on there? It will just suck heat from the joints and prevent the parts from self-aligning. The layout also looks wonky- is there actually solder mask on one of the pads? The chips should pull themselves into alignment by surface tension (well, unless the layout is unbalanced). – Spehro Pefhany Nov 08 '20 at 02:41
  • Reflowing like this should be pretty easy. If you're spending many hours and it isn't working, you're killing multiple parts, etc then you are fundamentally doing something very wrong. Explain exactly what you did (tools, materials, procedure, etc) and exactly what happened and maybe someone can tell you what you're doing wrong. Otherwise, your guess is as good as ours. – user1850479 Nov 08 '20 at 03:14
  • Double check the part rotation if you didn't already. – user57037 Nov 08 '20 at 03:25
  • Again, use a proper temperature controlled precision hot air tool, **not a "heat gun" !!!** – Chris Stratton Nov 08 '20 at 03:53

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