Electronics > Repair

Preheat temp setting duration when using AOYUE (etc.) 853A rework pre-heater

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wb0gaz:
Need to handle a small reflow task (this isn't a repair task, but this kind of requirement probably comes up during repair so thought i'd start here.)

I'm going to use an Aoyue (etc.) 853A rework pre-heating unit before hot air soldering.

Any guidance available on what temperature preset and pre-heat duration I should use?

Any guidance available on what workpiece temperature I should measure before using hot air to reflow?

Would a Flir-type IR imager be sufficient to measure temp of the workpiece?

Solder will be either 63/37 PbSn or 57Bi42Sn1Ag paste. The workpiece is small FR4 PCB.

Thanks  for any advice (or pointers to information on this topic.)

BreakingOhmsLaw:
Don't bother measuring the temperature, you don't need rocket science precision here.
I preheat to 125°C on lead free PCB and then spot-heat the areas of interest with hot air set to 360.
If you used Bismuth tin, you'll need to drop the temperature to 90 plate /145 air.

Don't throw the PCB on the already heated hot plate, start with a cold(ish) plate to reduce thermal stress.


wb0gaz:
Hello BreakingOhmsLaw, that is very much helpful!

1. I will begin from cold start on device, with workpiece already placed.

2. Shall I set pre-heat machine temperature (it's set-point for radiated heat) to 125C? For this pre-heat machine, there is ~2cm distance from thermal element (below) to workpiece (above), suspended by metal structure to keep PCB away from thermal element.

3. How long should I wait (once pre-heat machine reaches set point, until workpiece reaches OK temperature?

Thank you again!

Silicium81:
Hello,
I have a YIHUA 853A preheat unit. To get the PCB to 100°C, I need to set the heater temperature to 250°C. The safest thing is to measure the temperature of the PCB with a thermocouple!

wb0gaz:
That (preheat setting) was what I was completely uncertain about.

What do you use for a thermocouple, and how do you apply it for this purpose?

Thanks!

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