Preheating a board with large through hole components/modules on both sides

[potfish]

Hi

I have a PCB that uses thick copper and has through holes with no thermal relief. The boards were professionally assembled with SMT components on both sides and through-hole (large connectors etc.) on the top, but I need to add motor drive module that goes on the bottom side with through pins coming through to the top. I have good soldering iron and heat gun, but it's not enough.

I asssume that preheating the board will help a lot, and I'm trying to find the right equipment. The board is 180x120mm which rules out a lot of the small cheap heaters, and the module is 22mm tall so anything that just heats a local area probably won't do it. I think I need something to soak the entire assembly.
 
I need to buy something off the shelf in the US. I do not have time to build a DIY toaster oven, nor time to wait for something from China. I don't have a budget in mind, but I don't expect to use this regularly so I'd rather not pay too much money. If it's more than say $500 I would be better off just finding someone else to do the job for me.

Does anyone have any good suggestions?

Many thanks.

[Smokey]

Not the answer you are looking for....  but....
Redesign the board now and take the respin cost hit.  It will save you production time and money over the product life.
Thermal isolation around through hole pads is not rocket science. 

[potfish]

Thanks for the feedback, and I will consider that for a future rev, but for now I have to work with the board I have.

[thm_w]

You probably want to tape the module in place with kapton, preheat, then solder from the top side.

https://www.amazon.com/Preheating-Electronic-Preheater-Soldering-Motherboard/dp/B0CFTZKYTB
https://www.ebay.com/itm/326199890221

Other option might be some kind of griddle from a thrift shop.

https://www.eevblog.com/forum/reviews/recommended-board-preheater/
https://www.eevblog.com/forum/manufacture/yihua-preheater-853a/
https://www.eevblog.com/forum/manufacture/preheater-recommendation/

[ajb]

Other option might be some kind of griddle from a thrift shop.

Yeah, you don't need anything fancy here, and you don't necessarily need precision temperature control for the preheat (although that helps).  Heat loss is proportional to the difference in temperature, so go for a staged approach: A griddle or something that can warm the whole board up from underneath, then a hot air gun to further heat the working area, then a high capacity soldering iron to do the actual soldering. 

If you do use a griddle or hot plate for cooking, the temperature control will certainly be garbage by soldering standards.  A cheap Amazon temperature controller can help with that, and might be necessary to avoid overheating things if you end up with something that only has an 'off/high/low' sort of control.

[potfish]

Thanks for the links. I had read those threads already (I did try to search for a while before posting) and I am not sure how well a griddle would work when the board is separated from the heat source by 22mm. I would be heating the module nicely but not the board so much.

The hot air ones look better than a griddle for this, but my board is larger than those small, easily available ones can accommodate.

I was thinking one of the larger hot air preheaters would be best for this, but I cannot find anything that can be bought quickly in the US.

Edit: I decided to risk $80 on one of the cheap eBay IR ones, and we'll see!

[thm_w]

If there are other objects on the module side that have a height of 22mm, then yeah griddle is not going to work. If its just a short module then you could add sand or other transfer material to conduct the heat to the surrounding board. As a temporary method.

Alternatives for large hot air preheaters would be a temperatured controlled heatgun (wagner furno) or a general hot air rework station and a arm to hold the handpiece.
But I prefer IR over hot air preheat personally, as do most repair techs on youtube.

[langwadt]

If there are other objects on the module side that have a height of 22mm, then yeah griddle is not going to work. If its just a short module then you could add sand or other transfer material to conduct the heat to the surrounding board. As a temporary method.

Alternatives for large hot air preheaters would be a temperatured controlled heatgun (wagner furno) or a general hot air rework station and a arm to hold the handpiece.
But I prefer IR over hot air preheat personally, as do most repair techs on youtube.

I've seen some use old school halogen lamps

[CaptainBucko]

I use a paint stripper style hot air gun and a non contact thermometer. I choose a few points on the board to take temp measurements, and hold the board vertically, facing me. Once I reach the desired temperature, normally 125 deg C, I remove the board with leather globves into a position where soldering can commence. It makes a world of difference.

[Doctorandus_P]

A paint stripper (some experience to judge apprximate temperature / distance) combined with a thermostat is a nice and pretty universal combination for pre-heating objects. Thermostats are pretty much COTS products but getting them for the right temparature may be either industrial or DIY, paint strippers are cheap.

... leather globes ...

Are those for stumpy nubs?
(Stumpy numbs?)
https://www.youtube.com/@StumpyNubs

[Accu-Sembly]

Any chance you happen to be in Southern California?  Stop on by and use our selective solder machine with IR and convection preheat.  Our minimum is much less than the $500 you mentioned to have someone else do it.

If you had it professionally assembled in the first place, maybe that place would do your addition at reduced cost?

If you want to DIY, I know you are already aware of oven and hot plate options.  Do you have a high wattage iron?  What about two irons?  You can definitely power through a high copper plane with two irons at once, but risk of thermal damage is much higher.  Be quick and have appropriately sized tips.  I find that a >100W iron with a hoof tip that has a concave slot the exact size of my pin and barrel can also power through most thermal obstacles.  Like this:  https://www.jbctools.com/cartridges-category-4-design-Barrel-menu-4.html