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Old 11-07-2019, 02:00 AM   #1
caspian
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Default New Tiny Pad Installation

Dear Forum Members,

Yesterday, I removed a corroded IC from a laptop mainboard (as in the photo). During this process, Pad 19 got ripped off. This pad must be connected to the capacitor above it.
Unfortunately after cleaning, the ground copper appeared under Pad 19. I have to install a new pad on Pad 19. The new pad must not touch the the ground copper.

What is the cheapest substance or glue that I can use to cover the ground copper and install a new pad for Pad 19?
I do not have solder mask. Can I use any other substance for this work?
the substance must be heat-resistant as I will apply heat to solder a new IC on these pads.
What are your recommendations on this work?

Thanks
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File Type: jpg IBM-T61____after cleaning1.jpg (236.8 KB, 39 views)

Last edited by caspian; 11-07-2019 at 02:09 AM..
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Old 11-07-2019, 08:45 AM   #2
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Default Re: New Tiny Pad Installation

I'd recommend some sort of uv glue, epoxy or soldermask.
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Old 11-07-2019, 10:02 AM   #3
caspian
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Default Re: New Tiny Pad Installation

I was thinking of using Silicon Glue that can tolerate 200'C. It will cover the ground copper and will hold the new pad too. But I do know if it will be suitable for this job in practice.
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Old 11-07-2019, 11:33 AM   #4
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Default Re: New Tiny Pad Installation

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Last edited by budm; 11-07-2019 at 11:36 AM..
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Old 11-07-2019, 12:09 PM   #5
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Default Re: New Tiny Pad Installation

Why don't you just install the new ic, then run a thin wire from pin19 to the cap. There is no need to replace that pad, trying to will likely just result in a mess or more damage.

Last edited by R_J; 11-07-2019 at 12:14 PM..
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Old 11-07-2019, 01:13 PM   #6
caspian
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Default Re: New Tiny Pad Installation

Thank you.
I forgot to mention that the IC is QFN. So soldering a wire to it is difficult.
I thought there might be a standard way to repair such a damaged tiny pad. Is there such a way or I have to soldering a wire to the IC?
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Old 11-08-2019, 10:48 PM   #7
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Default Re: New Tiny Pad Installation

Quote:
Originally Posted by R_J View Post
Why don't you just install the new ic, then run a thin wire from pin19 to the cap. There is no need to replace that pad, trying to will likely just result in a mess or more damage.
Agree
Before placing the IC:
- Make sure ALL pads retain connection
- Lift / bend pin 19 before soldering the IC
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Old 11-09-2019, 06:04 AM   #8
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Default Re: New Tiny Pad Installation

Quote:
Originally Posted by megaraider View Post
Agree
Before placing the IC:
- Make sure ALL pads retain connection
- Lift / bend pin 19 before soldering the IC
QFN has no pins - it has pads like a socket775 cpu
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Old 11-09-2019, 12:02 PM   #9
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Default Re: New Tiny Pad Installation

Maybe you could find a similar trace from a scrap board, Then fill the hole on the board with a bit of epoxy, then position the new trace on top of the epoxy. that should prevent it from touching the ground trace below pin 19 and also hold the replacement trace in place.
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Old 11-09-2019, 07:31 PM   #10
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Default Re: New Tiny Pad Installation

Quote:
Originally Posted by stj View Post
QFN has no pins - it has pads like a socket775 cpu
Sure, that's why i mentioned "bend".
Most low count I/O QFN ICs usually allow the pads to be bent outwards the package (from backwards to the side).
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Old 11-09-2019, 07:57 PM   #11
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Default Re: New Tiny Pad Installation

no they dont, that's a PLCC package!
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Old 11-09-2019, 09:07 PM   #12
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Default Re: New Tiny Pad Installation

You may be able to tack a small wire to the side of the ic on the qfn
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Old 11-10-2019, 02:40 AM   #13
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Default Re: New Tiny Pad Installation

I'd use some Chemtronics thermal epoxy, it will take 315 șC for a minute. https://www.chemtronics.com/circuitw...hesive-syringe
Tin a fine piece of wire, lay it in place of the track, place QFN on top.
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Old 11-11-2019, 03:35 AM   #14
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Default Re: New Tiny Pad Installation

The last time I had to deal with something similar to this on a Macbook, the customer had already attempted the repair their-self and subsequent damage to the board exposed one of the internal ground layers. I back filled the exposed area with a hard curing UV solder-mask, the remaining arrangements were taken care of with several preformed copper wires soldered to their related nearby components or tracks tinned and positioned under the qfn pads. Thermal re-flowing completed the repairs to a satisfactory working standard. Suggest plenty of practise before attempting this.
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Old 11-11-2019, 03:11 PM   #15
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Default Re: New Tiny Pad Installation

Quote:
Originally Posted by stj View Post
no they dont, that's a PLCC package!
imo some QFN allow it to be done... or at least trimmed from backwards to the side (see picture attached to this post)
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Old 11-12-2019, 02:25 AM   #16
caspian
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Default Re: New Tiny Pad Installation

UV light is usually applied to a mainboard when there is no IC on it. But I have to apply it when there are various kinds of ICs on the mainboard such as CPU, North-Bridge, Embedded-Controller, Buck-Converters, Mosfets. but there is no UV-sensitive EPROM on it.
The mainboard belongs to IBM Thinkpad T61 laptop.
Can UV light damage any IC on this mainboard?
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Old 11-13-2019, 04:12 PM   #17
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Default Re: New Tiny Pad Installation

Quote:
Originally Posted by caspian View Post
The mainboard belongs to IBM Thinkpad T61 laptop.
Can UV light damage any IC on this mainboard?
No it won't. But protect your eyes!
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Old 11-14-2019, 08:06 AM   #18
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Default Re: New Tiny Pad Installation

I am working on iphone boards and most often there is a broken trace which needs to be repaired. 0.01-0.02mm wire, UV glue and UV lamp are very good for that job.

For your case 0.1mm wire should work fine. Just cover the ground with a very small amount of UV glue and let it dry under UV lamp. Then clean that wire, solder it to the capacitor and place it where it needs to be. Cut to lenght and apply a new layer of UV glue on it, let it dry under UV again.

Btw, that is far from tiny

Last edited by RethoricalCheese; 11-14-2019 at 08:34 AM..
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