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AuthorTopic: A4000 recap soldering problems  (Read 661 times)

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Offline David Wright

A4000 recap soldering problems
« on: October 04, 2019, 02:44:13 PM »
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For the life of me removing barrel type capacitor pins is too difficult. It seems flared and even after sucking with power sucker , still can't move it . Now they are busted off inside.
As for the lifted pad, how do I proceed on that?
« Last Edit: October 04, 2019, 02:46:49 PM by David Wright »
 

Offline Brian Hoskins

Re: A4000 recap soldering problems
« Reply #1 on: October 04, 2019, 03:01:54 PM »
I'm not certain what you mean by "power sucker", but I assume this is some form of solder removal tool which uses a vacuum in order to suck the molten solder away.  This type of tool is primarily for through hole components.

For a surface mount comonent, like the one you've shown, the problem is that solder will be underneath the leg of the component and you're not going to suck that out with a vacuum tool.  You're only going to manage to get the surface solder off, and then when you go to pull the component free it'll take the pad with it.

In future, it is best to remove this component using appropriate surface mount tools.  A hot air tool would suffice, but take care to protect the surrounding area - you don't want to blow off components you didn't intend to touch, or melt any surrounding plastics.  Also you need to be careful about how much heat is supplied (and how quickly).

I find it useful to reapply fresh solder to the joints before attempting removal.

Now, regarding your predicament, there are a few options you can consider. 

The best option would be a professional pad repair.  But for this you're going to need a suitable pad repair kit.  It basically involves replacing the lifted pad with a fresh one using adhesive.  You can buy kits with pre-made pads for common footprints, or you can construct your own pad out of copper foil.
Of course, I never damage pads myself  :-X but when I encounter damaged pads (such as corroded pads) I always construct my own replacements with copper foil.
Once the pad is replaced you obviously need to connect it back to the severed trace.  You will need to expose the copper on the end of the trace and apply some solder to join the new pad to the trace.

An alternative option, not recommended (because it isn't clean), is to simply run a small wire from the leg of the new component to a suitable connection point on the PCB.  That suitable connection point might be the end of the severed trace, provided you can anchor to it properly and secure it safely from being ripped up afterward.

There is a lot to consider here to be honest, much of which cannot be easily communicated with basic advice.  You may be better off enlisting the help of an experienced electronics tech to do the job properly for you.
« Last Edit: October 04, 2019, 03:15:44 PM by Brian Hoskins »
 

Offline Brian Hoskins

Re: A4000 recap soldering problems
« Reply #2 on: October 04, 2019, 03:07:14 PM »
By the way, I notice a label showing "pins stuck".  This is a through hole elctrolytic capacitor, right? How did you remove it? Did you simply cut it out?

To remove the 'stuck' legs, at this point the easiest way is probably to apply a soldering iron to the joint (with an appropriate head and adequate heat) until the joint is fully molten top and bottom.  Then, using a good set of needle nose pliars, gently extract the leg.  If you encounter significant resitance, stop and find out why - don't continue to apply more force.

My previous advice about applying fresh solder helps here, too.  Applying fresh solder will help transfer heat into the rest of the joint.

Once both legs are out, use solder braid to clean the joint of existing solder and expose the hole ready for the new component.
« Last Edit: October 04, 2019, 03:10:42 PM by Brian Hoskins »
 

Offline paul1981

Re: A4000 recap soldering problems
« Reply #3 on: October 04, 2019, 06:06:12 PM »
C185 - I wonder if the ends of the legs are bent under a bit on the other side of the board, as that's how they're secured initially if soldered by hand. Those through-hole types I'd always attack from the other side of the board anyway, not the component side. Melt the rear, then gently pull the component out with pliers or your fingers.

Offline Damion

Re: A4000 recap soldering problems
« Reply #4 on: October 04, 2019, 06:38:49 PM »
In lieu of hot air, I recommend using "ChipQuik" for the SMD capacitors. It significantly lowers the solder's melting point, and (in my experience) mitigates the risk of damage to pads already weakened by leaked electrolyte.

For repairing the pad, it can be done perfectly (so don't fret too much!), or as mentioned, a small bit of wire soldered to an adjacent via, or scrape away a bit of solder mask from the trace leading to the pad, and attach a small piece of wire there (about the length of the original pad), then solder the cap in place. (Kapton tape can be helpful, but it will be fiddly regardless.) These later methods can be reliable, but it's worth taking the time to learn to do "perfect" if at all possible (copper foil and adhesive).

In addition to what's been mentioned, a stainless sewing needle might help with the broken through-hole pieces. You can use a bit of ChipQuik on those too, carefully rock the part a bit at a time until it's free. However, a quality desoldering gun is probably the way to go here. Stay away from the cheap plastic "soldapult" type devices, the recoil causes the tip to nick the PCB, causing damage.

 

 

 
The following users thanked this post: Brian Hoskins

Offline Brian Hoskins

Re: A4000 recap soldering problems
« Reply #5 on: October 04, 2019, 09:47:06 PM »
I haven't tried 'ChipQuik' before.  I'd heard of it but couldn't say I really knew about it, if you know what I mean.

Anyway I checked it out and yes, I agree this would be a good idea - particularly in cases where you're dealing with pads which are compromised already by electrolyte or some other issue.  In those cases the less heat you have to apply to the joint to get the job done, the more likely that you can save the existing pad.

Also, for large SMT QFP chips, ChipQuik is undoubtedly a solution for people who don't have an expensive hot air kit with all the snazzy attachments etc.

Thanks!

Offline Vlabguy1

Re: A4000 recap soldering problems
« Reply #6 on: October 05, 2019, 01:54:04 AM »
I’ll fix it.

Offline David Wright

Re: A4000 recap soldering problems
« Reply #7 on: October 08, 2019, 04:48:32 PM »
Forgot to thank all for your input. Vlab offered to fix, hoping he still wants to.