Preheat temp setting duration when using AOYUE (etc.) 853A rework pre-heater - Page 1
Forum section: electronics / repair

author: wb0gaz
author_rank: Frequent Contributor
timestamp: January 18, 2022, 08:28:52 pm
content: 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.)

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: January 19, 2022, 01:00:20 pm
content: 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.

author: wb0gaz
author_rank: Frequent Contributor
timestamp: January 19, 2022, 03:32:06 pm
content: 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!

author: Silicium81
author_rank: Regular Contributor
timestamp: January 19, 2022, 03:58:21 pm
content: 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!

author: wb0gaz
author_rank: Frequent Contributor
timestamp: January 19, 2022, 04:02:57 pm
content: 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!

author: Silicium81
author_rank: Regular Contributor
timestamp: January 20, 2022, 08:18:22 am
content: The thermocouple bracket:In fact, I made a small system to be able to remove the BGA (and put them back after reballing). The thermocouple is used to regulate the upper circuit temperature by generating a controlled reflow profile. But before starting the upper heating, it indicates the temperature due to the lower heating.https://vae-tech.forumactif.org/t239-reparation-bga-ou-rebillage(in french)(sorry for my english 'google translate')

author: wb0gaz
author_rank: Frequent Contributor
timestamp: January 20, 2022, 03:01:12 pm
content: Thank you excellent detail!Hope for BGA in future!!!Now I will find DMM + Thermocouple solution.Thank you again,Dave

author: Silicium81
author_rank: Regular Contributor
timestamp: January 20, 2022, 08:22:41 pm
content: Thank's, For low price thermometer with thermocouple, search TM-902C on aliexpress

author: wb0gaz
author_rank: Frequent Contributor
timestamp: January 20, 2022, 09:18:33 pm
content: Thanks so much, Silicium81!I had searched unsuccessfully for that sort of device, evidently wrong search terms.Order now placed.Very much appreciate your helpful detail - this is how to solve the requirement!Dave

author: testpoint1
author_rank: Frequent Contributor
timestamp: January 21, 2022, 06:45:06 pm
content: Quote from: wb0gaz on January 20, 2022, 03:01:12 pmFluke 87V and 80BK-A probe

author: wb0gaz
author_rank: Frequent Contributor
timestamp: January 21, 2022, 08:04:29 pm
content: Rats - I knew i had a thermocouple probe somewhere, came with a DMM, long since lost...Oh well, that's a helpful pointer!Dave