IC pads are a missin'

So after using a solder sucker on some IC pads, they lifted off. I was able to pathetically push one back into its place but I’m still worried about the results. I still see metal on the inside of the hole. It’s on a voicecard and not Mobo which is a blessing. Can you guys give me some advice when it comes to soldering those bad boys? what I should possibly expect on power up? I’ve seen some bridging techniques on the online but I figured I’d ask trusted folks. Thanks

Look at the schematics to check what the pad was connected to, and recreate the connection with a piece of wire directly between the two parts.

An aside,
I had to try replace the dc jack on my microKorg XL recently , firstly the dc jack is a proprietary make , standard 3 leg offset wont fit , and I managed to lift a couple of pads -, I was not abusing the pcb , yet the pads slid off like decals. I ended up drilling a new hole in the case, putting in another type of jack and bridging to elsewhere on the circuitboard. Crap build quailty , Mr Korg!

Do the top side pads matter with the ICs? Following the SMR4 chart it seems what i broke is whereIC3 hooks up to C8. Is this what I should solder on the underside?

Top sides are connected to the bottom sides anyway…

Now for the reason the Pads came off: you are working at to high temperature and/or Leadfree solder. I use leaded Solder only and 303°C (yeah the number is a reference…) and simple approx 1,5mm DesolderingBra(i)d™ and i can desolder a LCD falling out without without tearing apart anything. Although the white silkscreening will look slightly burned…

I meant, do I need to solder top and bottom with homemade connections or will bottom get the job done?

I am not sure I understand your problem. Don’t bother with the PCB. Connect the socket or IC pin to the component lead.

Ah, i see, he wants to know it the Pad itself sometimes is used as a Via?

Ah yes, I see the problem now. Sometimes a pad is used to connect two components, so you’ll need to recreate both connections. Can you tell me which pad/pin we’re talking about? You mention IC3 and C8 but they are not connected… Let me know the IC number and pin number and I’ll tell you what it is hooked to.

Pin 15 on IC 3 LM13700N that has a trace connected diagonally to C8 100N

Oh crap, I was looking at the Shruthi SM4 mkII board :frowning:

So C8 is a bypass cap. There’s an enormous chance the circuit will work well without it :slight_smile:

The only important thing is to make sure that pins 10 and 12 of the IC are connected together.

Those should be directly connected with a wire because I borked the bypass? Or just make sure those are finely soldered?

No. Pins 10 is connected to a pad, which is connected to a PCB trace, which goes to a pad, which goes to pin 12. Looks at the PCB image closer - the trace that goes from pin 10 does not go to C8 - it snakes between the capacitor pins and goes to pin 12.

Since you have destroyed pad 10, this connection is destroyed, so you need to connect pin 10 to pin 12.

I’m a bit excited to do this, I really appreciate you giving me the “why” behind everything. You are a yogi of electronics and it is great to be enlightened as I enjoy this facet of reality. And I’m glad I know how to count those pins. Are your IC’s always counted counter-clockwise? I asked google how to count IC pins and a company depicted it as such:

9 10 11 12 13 14 15 16
1 2 3 4 5 6 7 8

Here is the result of your suggestion, let me know if its too sloppy or something. I have noticed that pad 11 on IC3 of another voice is also gone. That looks like it hooks up to C8?

Pad 11 goes to C8 but don’t bother.

If you want to check your hob, use a multimeter and check that there is continuity between the things that should be in contact, and not between the things that shouldn’t be in contact…

It was the first thing I did and great success! I’m cool with forgetting about it, but would you like to let me know why pad 11 and C8’s relationship isn’t necessary?

C8 is a bypass capacitor. It serves as a local energy reservoir in case the op-amp or OTA needs a sudden surge of current (it might take a while otherwise for the regulators to adjust to the change in demand, causing a temporary voltage variation on the supply rails, which can, in some circuits, leak into the audio path). There are cases when not having them causes instability / noise. Instead of learning the hard way (ie, once a proto has been built) when and where they are needed, it is a common practice to put such caps everywhere (a 100nF on each power pin of each IC, and a bigger one in each subsystem and/or near parts that switch a lot or do A/D or D/A conversion.

On these filter boards, I doubt there are large change in the current taken by the LM13700, and if it happens, there are bypass caps on the nearby chips to provide for some current.