Kapton tape and heat guns on retro boards

[msknight]

I'm continuing my learning on soldering, desoldering, etc. and I've invested in a heat gun to assist desoldering large chips/sockets on retro 8 bit electronics ... (I'm continuing to work on my de-solder gun technique, but I'm not there yet) ... and someone advised using Kapton tape to protect other components.

I'm using about 340c at low volume and it seems that as some of the heat is transmitted through the board, I was wondering what use the kapton tape will be to me ... presumably because I believe the main aim will be to deflect heat flow away from neighbouring chips and not... as I read others using the tape for... for its adhesion. As my purpose will likely be to prevent the heat flow from reaching other components, is there something else, preferably re-usable, that is employed instead for this purpose?

Grateful for advice please.

[Gyro]

Kapton tape is most useful for preventing nearby components from being blown away by the air blast. If you want to reduce heat spread, taping Aluminium foil around the area to be heated is very good for conducting excess heat away.

[Gyro]

I was just re-reading and noticed that you are mostly working on through hole stuff. In this case, there is obviously no risk of blowing parts away but the Aluminium foil is still useful for limiting heat spread.

It sounds as if you are being a little cautious on the airflow. You really want to get sufficient heat into the area in the shortest possible time. This implies h`igher airflow and shielding, rather than an extended period of slow heating, which encourages transmission of heat to other areas. The airflow is a balance thing between excessive dwell time and de-laminating the board that comes with practice.

[RoGeorge]

Kapton or Al foil might help, they might be reused a couple of times if needed.

What's way more useful to ease desoldering is a preheater.  Place the preheater underneath the board, such that a large area is pre-heated (at a temperature lower than melting point), then use the hot air station from above to add the higher temperature air that will melt the solder for the wanted chip.

The preheater can be bought, but after all it's just a source of heat.  Doesn't has to be rocket science, I've seen cheap halogen light bulbs used to improvise a preheater (the kind of bulbs for ceiling spot lights).

[msknight]

Regarding the pre-heat side, I am using the desolder station to heat the lower side of the board before moving to the top.

I'll certainly look at delivering more heat, faster... and certainly using some aluminium foil to deflect.

Thanks very much for all the advice.

[jpanhalt]

I agree with the use of aluminum foil to shield.  It does not have to be applied tightly.  In fact, I tend to wrinkle it a little (visualize the heat shields on spacecraft).  Kapton tape, of course, can be used to hold it down, but is usually not necessary in my limited experience.

[RoGeorge]

heat the lower side of the board before moving to the top

Try heating from both sides at the same time, a pre-heater underneath, and once the bard got hot let it running while adding an extra heat (at higher temperature) from above, only where the chip to desolder is.  That was very help for SMD, but I wouldn't try hot air at all for 8bit vintage computers and alike through holes.

The most successful way to desolder those (from when I was builsing Z80 computers) was to use a syringe needle of 0.8mm external diameter.  It's inner diameter was just right so a normal IC pin can fit inside the needle's hole, like this:





That is meant to be used with a normal soldering gun or iron.  Put the needle on top of the pin, and rotate the needle while heating the solder pad.  Eventually the solder will melt, and the needle will "cover" the pin, passing through the PCB hole.  Once it passed through the other side, remove the soldering iron and keep twisting the needle back and forth (so the solder wont stick to the needle), until the solder pad solidifies back.  Do that for each pin of the IC.  In the end, the IC will almost fall out by itself.  Works very well for those IC for which the pins were bent to anchor the IC to the PCB (at the factory, before soldering).  Second picture is to illustrate the idea better, that IC was never soldered there.

I wouldn't try hot air on anything through-hole technology.  In case you don't have the right needle diameter, there are ready-made desoldering needle tools (with a handle, too).


If you already have had success desoldering THT chips with hot air, and only need some reusable heat deflectors, maybe cut out a silicone mat for the shape of a single IC, or DIY some funnels-like out of aluminium foil (to guide all the hot air only on top of the chip to desolder).  There are some single-use food plates (and disposable launch-boxes) made out of a much thicker Al foil then normal Al wrapping foil.  I used the thicker material a few times.  It can easily be formed in the desired shape, yet it is thick enough to maintain its form.

As for reusable kapton-like, cutting out template forms from a silicon mat should work.  There are some 5mm thick translucent "soldering-helper" silicon mats, too, and they are outstanding heat isolators.  There are some high-temperature resistant silicon mats (sold as mats for oven cooking), in case you want thinner material than the soldering silicon mats.

Another aspect to the 5mm thick soldering silicon mat is that the material is also a great reflector for heat, so if you just sit the PCB on the silicone mat and heat with air from above, all the heat that manage to pass through to the other side of the PCB, will be reflected back to the PCB.  The reflected heat from the mat helps almost as much as a preheater.  The material looks like these:

https://duckduckgo.com/?q=translucent+silicone+mat+high+temperature+resistant&iar=images&iax=images&ia=images (the one I've tried so far is the translucent/slightly transparent kind).

[tatel]

Perhaps you would consider using something like a desoldering gun. I works very well for me. I have no more problems desoldering through hole components. It's now an easy and quite fast task.



https://aliexpress.com/item/32957483227.html

[msknight]

I do have a desoldering gun, but I'm continuing to get sweat joints despite continuing to try with it. Hence the minimal heat to just kick the sweat joints enough to finish the job.

Next trick is to try adding solder to the old joints before I attempt to desolder.

[Gyro]

If you're working on old 8 bit stuff, it is almost certain to be using Leaded solder rather than higher melting point Lead free. Adding some 63/37% might bring the melting point down by little bit though, just not as much.

[MathWizard]

That's a nice trick with the needle for de-soldering stuff.

Does anyone ever use fibreglass insulation from something like a furnace or boiler ? I remember a video of a train mechanic holding a piece on his glove and hitting it with I believe an Oxy-Acetenlyne torch, and it doing nothing.

Fibreglass fibre's are not nice to work with, but maybe they use it in some industrial soldering settings ?