Reflow Oven Replaceable With A Heat Gun?

[bmarc92]

TL;DR Summary

Looking to see if a reflow oven can be replaced with heat gun

I was looking to get a reflow oven but now I am wondering if the same effect can be accomplished with a simple heat gun. It's a little extra effort, but not sure if the convenience of a reflow oven justifies the cost difference. I mean, it just has to reach a certain temperature right?

 

[berkeman]

How big is the section of the SMT PCBA that you want to solder? For small areas, Hot Air SMT Rework wands are common to use. For anything bigger than a square cm or two, you will need at least a small reflow oven to solder your PCBA.

https://www.adafruit.com/product/3941

 

[bmarc92]

How big is the section of the SMT PCBA that you want to solder? For small areas, Hot Air SMT Rework wands are common to use. For anything bigger than a square cm or two, you will need at least a small reflow oven to solder your PCBA.

View attachment 341369
https://www.adafruit.com/product/3941

What is the reason for the dimensional constraints?

Let's say I have a board 3x6 in. Once I have my components and soldering paste in place, where might the difficulty from the dimensional factor come into play if a heat gun were to be used?



P.S

(off topic)
I could not reply to your message regarding the double accounts, I kept getting a "spam" msg error for some reason.. I'll go with this account Bmar92, thanks-

 

[berkeman]

What is the reason for the dimensional constraints?

Let's say I have a board 3x6 in. Once I have my components and soldering paste in place, where might the difficulty from the dimensional factor come into play if a heat gun were to be used?

One issue is dealing with closely-spaced SMT components. As you solder one, you can desolder an adjacent one and blow it askew on its pads. You can get directed nozzle attachments that can mitigate this, and you can design your PCBAs to be easier to rework/solder (space the components out more, which results in increased PCBA area and cost).

How many PCBAs do you need to solder? What size components are used, and how closely are they packed?

 

[Borek]

Depending on the size of elements involved blowing them out can be a serious problem. Low airflow helps, but only to some extent.

 

[Rive]

I was looking to get a reflow oven but now I am wondering if the same effect can be accomplished with a simple heat gun.

In this business a 'simple heat gun' may be OK for some destructive desoldering job only.
With some experience they might be used for pre-heating, but still not proper.

For proper soldering work you need one with finely adjustable airflow and temperature, and it'll still work only with serious constraints (the locality of the heat and the mechanical effect of blowing wind can be quite troublesome).
For multi layered bigger PCBs a HotPlate may be able to mitigate that to some extent, but at the end, soldering work is for (soldering) irons and (reflow) ovens.

 

[Averagesupernova]

In the past I've done thousands of rework jobs with a heat gun. Mostly SOICs, a few PLCCs. It's going to depend on several factors. How much air blast is coming from the gun to blow parts around if they were not glued down, and experience of the operator are the main ones. Very steady hands and a cool head are required. A good tool to lift the part off helps a lot.
This one for instance:
https://www.amazon.com/Jiayouy-Extr...nt-Placement/dp/B08V8W39FQ/?tag=pfamazon01-20
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With experience I was able use a good pair of tweezers.
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Disclaimer:
The boards I reworked were of decent quality. Some consumer grade stuff I'm surprised make it through assembly. They may not survive rework at all.
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Before placing the new part back on the board, add a dot of solder to each pad. Again, experience will help here. Place the new part on and apply heat. When the solder melts, tap the board lightly. This action causes the surface tension of the molten solder to pull the part into place. If your heat gun moves the part around you have to much air blast. I never had this trouble. Had the right gun I guess.
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I assume you are trying to accomplish rework and not first time assembly. Unless you are doing first time assembly on very low parts count boards in small numbers I don't know why you wouldn't have an oven of some kind.

 

[TheJerC]

From experience, you can get away with using a heat gun up to a certain point. You're going to get varying results dependent on your dexterity and experience with a heat gun. An oven is going to get much more uniform results.