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After having spent 4 hours to hot air solder, multimeter probe, apply flux around the sort circuiting pads, re-hot air, re-probe and finally apply wick & iron to get rid of those shorts I am now concerned with possibly having overwicked them. I can't tell for sure if there is pin to pad connectivity and wouldn't know how to test for it. Also, I wouldn't want to go on soldering the rest of the board only to find out at the end that my no lead packaged chip is not working.

Is there any way I could test this connectivity for a LGA package? It does not expose its pins on the side, it only has bottom pins. I don't know if the multimeter probes are touching the solder joint or just the bare solderless pads underneath.

I tried the resistance to GND measuring method from this answer. My joints are a wreck... Aside from that, I can understand cases 1 and 4 below, but how about 2 and 3?

  1. DMM reading of 1.4 M - probably for the healthy solder joint
  2. DMM reading of 1.0 M - how so?
  3. DMM reading all over the place, or slowly decrementing, or slowly incrementing
  4. DMM reading out of range - probably no contact between the pin and pad
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    \$\begingroup\$ An x-ray machine helps. But lacking that, you would produce two boards, and use one as a test jig for the other which only has the chip and test points to the first. If this is a one off, that sucks. \$\endgroup\$
    – Passerby
    Nov 22, 2017 at 10:26
  • \$\begingroup\$ @Passerby Well, no X-ray machine on my desk... Could you elaborate on the test jig ? I don't understand how that works. \$\endgroup\$
    – kellogs
    Nov 22, 2017 at 10:30
  • \$\begingroup\$ @kellogs if your chip has ESD protection diodes on its inputs, you can probe to GND or VCC with a diode tester. \$\endgroup\$
    – Manu3l0us
    Nov 22, 2017 at 10:30
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    \$\begingroup\$ You build one board that has everything except that chip. You build another that only has that chip (basically a SMD to DIP type adapter). Then you connect the two to test it. If it works like intended you likely soldered it correctly. \$\endgroup\$
    – Passerby
    Nov 22, 2017 at 10:32

1 Answer 1

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Curve tracer maybe? That's a homemade one. In the factory you usually x-ray, then put the board on a tester that does something similar. If you have a known good board you can probe it and get the resistance to gnd, to other pins. Then as @Manu3l0us suggested your diode tester to GND or power. Then compare between your board.

If you don't have any tools... Turn it on and start probing to see if it works.

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  • \$\begingroup\$ nice! can you take a look over the edit in my OP ? \$\endgroup\$
    – kellogs
    Nov 22, 2017 at 16:42
  • \$\begingroup\$ For number 3 I expect some capacitance attached tot hat pin somewhere? \$\endgroup\$
    – Some Hardware Guy
    Nov 22, 2017 at 16:44
  • \$\begingroup\$ yeah, probably, or some semiconductor logic kicking in. I don't suppose that some variance of the read resistance within +/- 25% would cause any issues now, would they ? I mean same points measured in different boards. \$\endgroup\$
    – kellogs
    Nov 22, 2017 at 17:58

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