[Coco] Sort of OT: Recapping

[Rick Ulland]

Hit send to soon. Hot glue is not conductive and sets so fast you can 
hold your part a bit off the board to insulate it from the traces you 
have just glued it on top of.



On 11/28/20 5:32 PM, Rick Ulland wrote:
> I've got to admit, without tools I would probably just stick a new cap 
> to the board with hotsnot and tack it to the remains of the old leads....
>
>
>
> On 11/28/20 2:38 PM, Richard Lorbieski via Coco wrote:
>> The problem is not with the copper thickness or amount of layers. 
>> Most IBM retro motherboards (1990 era) are 6 or more layers.
>>
>> The three most common problems that occur with DIP multi-layer rework:
>>
>> 1) Failure to get the lead(s) out of the thru hole ground/power plane.
>>
>> 2) Old solder clogged inside the thru-hole of via.
>>
>> 3) Damage to the thru-hole plating (most catastrophic).
>>
>> I discourage the use of sharp objects or using brute force can lead 
>> to damage the plating and thus cut the connection between internal 
>> and surface pads of the PCB.
>>
>>
>> On 11/28/2020 6:55 AM, Dave Philipsen wrote:
>>>
>>>> On Nov 27, 2020, at 11:09 PM, Richard Lorbieski via Coco 
>>>> <coco at maltedmedia.com> wrote:
>>>>
>>>> Based on the photos, this is a multi layer IBM clone PCB with 
>>>> possible internal ground and power planes.
>>>>
>>>> The problem is that the heat is being dispersed onto the ground (or 
>>>> power) plane and not enough heat is being applied to the solder.
>>>>
>>>> This kind of rework requires more than a 70W soldering iron.
>>>>
>>>> You will need a rework station with a heat gun and possibly a 
>>>> variable convection type oven.  A conventional oven could damage 
>>>> components on the PCB or melt some of the plastic parts. You will 
>>>> also need a soldering iron that is capable of reaching 900F and use 
>>>> a proper solder tip. Most consumer soldering irons usually reach 
>>>> 600F-650F.
>>> You could even use a larger Weller “soldering gun” (you know, the 
>>> one that actually looks like a gun!) to heat it up enough (for the 
>>> weekend hobbyist who doesn’t do enough of this sort of work to 
>>> justify the cost of a hot-air rework system or an oven). Keep a 
>>> slight pull on the cap lead while heating the joint. As soon as the 
>>> solder melts you pull the lead out and remove the heat of the gun. 
>>> On radial lead parts like those in the photo you may have to 
>>> alternate back and forth between the two leads a couple of times to 
>>> “rock” it out.
>>>
>>> Practice on a junk board first until you feel comfortable with it.
>>>
>>>> I also recommend NOT to sharp knives or force the leads out of the 
>>>> PCB. This could damage the internal connections on the PCB.
>>> Although I would only recommend cutting the connection to the ground 
>>> plane as a last resort, I would have to disagree with your comment 
>>> on not using a sharp knife to cut the copper foil. The copper is 
>>> relatively soft at a thickness of maybe 2 thousands of an inch. An 
>>> Exacto or similar knife can cut through it fairly easily. However, 
>>> the prepreg layers used to separate an internal copper layer of a 
>>> 4-layer board are going to be probably more than 7 thousands of an 
>>> inch thick and *much* tougher to cut through than the copper. When 
>>> cutting through copper traces/planes it is very easy to see when 
>>> you’ve gotten through the copper and reached the substrate. If you 
>>> are fearful of cutting too deep, use less pressure on the knife and 
>>> several successive cuts to get through the copper. I have never cut 
>>> a trace deep enough on a multi-layer board to damage an internal layer.
>>>
>>>
>>
>