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Hot Air Gun Issues
Old 5th June 2019
  #1
Gear Head
 

Hot Air Gun Issues

Hey,

Newbie modder and having some real issues using a hot air gun. Purchased a Kendal 853D rework station and when soldering with the iron at 375 on an old pcb (assume it's 60/40 solder and using no clean tacky flux) I have no issues and the solder melts after about 2 seconds, but the second I try to use the air gun it all falls apart.

With the air gun at the same temp and flux it almost doesn't melt and I've actually burnt the practice board. I've tried various tips, higher temps and air flow settings and nothing seems to work. I've watched a ton of vids and I really just can't figure out what I'm doing wrong.

Here are my questions:

1) Generally speaking I should be at the same temp for air as iron, correct?
2) How does air flow affect the process? Should it be off/low or high?
3) I should be about 1/2 an inch to an inch off the pcb and parallel to the board?

What else am I missing or doing wrong?
Old 10th June 2019
  #2
Lives for gear
 
ulysses's Avatar
I was surprised to learn I need much less air flow than I had expected. I'm doing new assembly, with stenciled solder paste and hand-placed SMD components (0805 is about the smallest package I use). Too much airflow and the components get blown out of position, so I'm using a rather light flow.
But I'm also preheating the board from underneath. That might be impossible if you're reworking assembled boards that have components on the opposite side. I don't have a dedicated preheater plate as I'm only doing prototyping, I actually use my glass-top electric stove, but the effect is the same. At first I found it impossible to get solder flow without preheating, although now that I've gotten better at it, and have a decent hot air system and have my settings settled in, I find that I can in fact flow solder without preheating if I have to. And I'm using SAC305 solder (lead free) with a higher melting point. I'm also using water-soluble organic flux, which means extremely thorough washing is mandatory when I'm done, but it also improves my solder flow quite a lot in my experience.
Old 10th June 2019
  #3
Gear Head
 

Quote:
Originally Posted by ulysses View Post
I was surprised to learn I need much less air flow than I had expected. I'm doing new assembly, with stenciled solder paste and hand-placed SMD components (0805 is about the smallest package I use). Too much airflow and the components get blown out of position, so I'm using a rather light flow.
But I'm also preheating the board from underneath. That might be impossible if you're reworking assembled boards that have components on the opposite side. I don't have a dedicated preheater plate as I'm only doing prototyping, I actually use my glass-top electric stove, but the effect is the same. At first I found it impossible to get solder flow without preheating, although now that I've gotten better at it, and have a decent hot air system and have my settings settled in, I find that I can in fact flow solder without preheating if I have to. And I'm using SAC305 solder (lead free) with a higher melting point. I'm also using water-soluble organic flux, which means extremely thorough washing is mandatory when I'm done, but it also improves my solder flow quite a lot in my experience.
I use no clean flux and added various amount, but I did notice last night when fixing my wife's hair dryer that the tubes to melt over the wires have 125C listed on them as their reacting temperature, but I had to go up to almost 225 before they really shrunk in to place at a reasonable speed.

I think I'll give it another go later this week on my practice pcb and crank it way up to 475-500 and see.
Old 10th June 2019
  #4
Lives for gear
 
ulysses's Avatar
And you're sure your hot air gun isn't calibrated in degrees Fahrenheit?
Old 10th June 2019
  #5
Gear Head
 

Quote:
Originally Posted by ulysses View Post
And you're sure your hot air gun isn't calibrated in degrees Fahrenheit?
I'm 99.9% sure, but I'll double check
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