T962A SMD Reflow Oven Fix/Hack

About: I am an electronic artist living in Brooklyn, NY. I work with LEDs, microcontrollers, and analog electronics to create objects that I find beautiful.

I've recently purchased a popular T962A SMD reflow oven. The reviews are split on this oven - some find it to be quite acceptable, while others find it completely useless. After much researching, I decided to give it a try.

(Feel free to skip this part if you already have the oven.)

T962A is an inexpensive IR (infrared) SMD reflow oven. It has a microcontroller to control temperature and timing (profile), so you can basically put populated PCBs in, push the button and simply wait for a few minutes. Then the PCBs are done.

There are some issues with this oven, but my experience is rather positive overall. For my purpose this oven works well.

However the problems are:

1. The oven produces horrendous smell.
I'm not taking about the smell of solder paste melting. The oven itself produces the smell even without anything in it.

2. The heat distribution is not very even.
This is not an issue with leaded solder, but becomes a major problem with lead-free solder. As lead-free solder requires much higher temperature to reflow, the extra temperature needed to ensure the solder reflow on all parts of PCBs can burn the parts in the hot spots. Even though I'm lucky enough to not fry any PCBs with this oven, some parts did come out looking burned.

I want to share what I did to improve on those issues.

Step 1: Why So Smelly?

Like any oven, I expected some odor/fume to come out on the first few runs. But this oven is no ordinary oven in that respect.
Upon its first run, it produced something that I have never smelled before. It was so toxic, that it gave me a bad headache. And the smell did not go away even after a few runs.
So I decided to open it up and see what's causing the odor.

Opening the hood was quite simple, just pull the drawer out, and remove a few screws. Then the top is open.
Then there was the source of the problem - masking tape! Masking tape is used to prevent electrical shorts between the aluminum foil used to cover the insulation material and the controller PCBs. Even though there's heat insulation material beneath it, the tape gets hot enough to produce that nasty odor. So I removed all of the masking tape, and replaced it with Kapton tape, which is heat resistant.
(Sorry I forgot to take the picture of the masking tape before removal. You can see some pics here though.)

This mod took care of the odor completely.

Step 2: Improve the Heat Distribution

Looking at the inside of the oven, got me thinking - is there any way to improve the uneven heat distribution?

Infrared reflow oven has an inherent weakness - because the infrared heat is absorbed at different rates depending on the surface color, black ICs get heated up quickly, yet metal parts heat up slowly. Temperature profiles are used to give some "soak" time to let the temperature even out between different parts of the PCB. However that can only help so much.

Modern reflow ovens mostly use convection technology. Convection ovens use moving air to deliver the heat. This method distributes heat much more evenly then IR method.

T962A has a cooling fan in the back. This fan sucks air into the oven to cool down the inside. The heated air comes out of the bottom of the oven, which has many slots.

So I thought, why not use this fan to give some air movements during the heat up, to help distribute the heat?

Looking at the controller closely, it is revealed that:
  1. Heating elements are controlled by a SSR (Solid State Relay) via 5 V logic voltage from the controller.
  2. Fan is control in the similar mannor - logic signal controlling a triac via an opt-coupler.
Which means that I should be able to sense whether the heater is on or off, and turn on the fan as I wish.

I connected four wires to get the necessary I/O out of the controller board. and routed the wires out. Connecting the switch to the fan controller line proved that it works.
(If you are doing this please see comments on the photos - there are some importent information in there.)


Arduino to the Rescue

Now I got the signal that tells me whether the heater is on, and a line that lets me turn on the fan when I want. I believe by blowing just the right amount of air when the heater is on would improve the heat distribution. So I took out my Arduino, and wrote up a simple code. The code basically senses if the heater is on, and if it's on runs the fan at a low speed. To run the fan at a low speed, I chose to do super low frequency PWM, which ended up being turning on the fan for 0.1 to 0.2 seconds, and turn off for 0.8 - 0.9 seconds. I did it this way instead of using Arduino's PWM output, because the fan controller may not respond well to the signal going on/off hundreds of times a second. I'm using 15% duty cycle to run the fan.

By running the fan slowly enough, the hot air inside is moved around to help distribute the heat. The heater is strong enough to still heat up quickly.

The result is an improved heat distribution, and seemingly more accurate temperature reading. I think the air movement helps the thermocouple (temperature sensor) inside the oven to sense the air temperature.

More testing and tweaking might be needed to get the most out of this modified oven. But so far I'm very happy with this.

2 People Made This Project!

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41 Discussions

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davidelvig

1 year ago

Thanks for this. I saw it pre-purchase, and it made me comfortable enough to buy. I'm surprised that in 2 years they have not addressed the masking tape issue. Must be tight margins.

Opening, removal of masking tape and replacement with caption tape, and reassembly worked like a charm. Front screws were a bit fussy... they are stripped-ish. Reassembled well. First fire-up - still pretty smelly.

I'll do another run and see how it goes..

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nomuse

2 years ago

Kapton tape worked like a charm. I didn't smell anything nasty when I fired up the oven for the first time. Maybe I'll try the fan controller next -- but you know what would be kinda cool? A light.

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AndyZ8

2 years ago

I did your improvements on the oven with the exception that I cut the connection from the fan - line, put the one side to an other input of the arduino and an other output from the arduino to drive the fan, as you did. In the software I did also the check, that if the heat is off, and the fan is on, I switch on the fan constantly

Now I did two measurements, first I put a PCB in with a underlay of about 6mm. On this pcb I put a temperature probe. During the process I also took time and compared with the time of T962. I realized two points:

1st: the temperature on the display is about 20 - 30 Kelvin below the measured temperature on the board. That means, at a display temp of 160°C I had about 180 - 190°C on the board. The higher the temp, the smaller the diffrence. At about 250°C, the board temp was about 265°C.

2nd: the time for the process took on the display 8mins. I took a time of 12minutes which is 1.5 times more!!

At the company where I work, we have a Protoflow E reflow oven from LPKF. We have really good results with lead free soldering. I put in that soldering curve, which gave us really good results....
First heating up to 160°, holding the temp, than put in the PCB and as the temperature reaches again 160°, it pre-heats the pcb of at this temp for about 160seconds. Than it goes up to 260° during 100seconds, that means a ramp of 6K per 10 seconds. At 250°C we need to open the door at the LPKF, but the origin curve goes than down with a ramp of 10K per 10 seconds.

About the much higher temperature: Has anybody made the same experiences that this temperature is this higher than the displayed? If this is really ture, I need to take down the whole diagram of about 20K. And about the time, I need to shorten the whole time range at factor 0.66.

This to much of temperature might be THE reason why so many people get burnt components during lead free soldering with curve 3. I have tried this curve, had also burnt components and bad solderings.....

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Mike6158

3 years ago on Step 2

I just bought one of these ovens. I'm sure glad that that you wrote this up

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WulfM

3 years ago on Introduction

I would like to know why if you have firmware for the unit you also need an arduno to control the fan. seems to me if you have working source code you can just pwm the fan as you see fit.

I just bought an oven and got it today and am thinking about doing a full schematic on the controller board.

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wj_xnk

3 years ago

The controller project is hosted here: https://github.com/UnifiedEngineering/T-962-improvements

DSC_0366.JPG
4 replies
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wj_xnkwj_xnk

Reply 3 years ago

My alternate firmware project that is.

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ledartistwj_xnk

Reply 3 years ago on Introduction

That looks very impressive. I will check into it. Thank you very much for sharing!

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wj_xnkledartist

Reply 3 years ago

I got inspired by your Kapton tape mod and got carried away a bit so I wanted to share my findings here.. :) At least it will show people how the hardware is wired to the controller MCU. Everything but the buzzer is operational (and the buzzer is a simple known gpio pin)

Thanks very much for this tutorial. Was good tech review before I bought one, just saved me to make the entire house smell bad for that useless masking tape. Anyway I made your mod with the Arduino, works fine definitely the temp in the oven is more even across the surface. However my oven still burns PCB's!. The issue is more likely to be caused by timing, as varying the reflow graph I get different outcomes ( sometimes burned, sometimes solder did't melt). I first tried to change the crystal as hoping that will fix the issue, (originally has 11mhz mounted on) 12mhz improves but not enough, 14mhz the display will not display characters properly. At the end I gave up with the idea of fixing the timing, and went back trying creating a new reflow graph including the time offset. So far no luck in creating an ideal graph for Leaded 63Sn/37Pb paste, with this oven. There is any chance that you can share with us your adapted reflow graph, showing time Vs Temp, that will be really helpful.

The T962-A is a such good oven, is a shame that they made a mess with the software. I noticed that the board as all the capabilities to drive that oven properly, and luckily there is an ISP connector for programming. I hope that maybe one day someone will create an updated firmware for it...

5 replies
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wj_xnkfederico.mari88

Reply 3 years ago

I've put some effort into an alternative firmware for the LPC MCU present in the original controller. I have also enabled the fan to run during the reflow cycle, and it definitely helps as long as it doesn't run too fast. Reaching peak lead-free reflow temperature is challenging when fan runs faster than minimal speed.

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federico.mari88wj_xnk

Reply 3 years ago

Great someone finally put the effort in doing that. Did you solve the timing issue? I think that the best way to solve the problem of no airflow, is to add an internal fan (as conventional cooking ovens). Any chance you can share the firmware with us?

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wj_xnkfederico.mari88

Reply 3 years ago

Firmware linked in the comment above. Timing is proper, but the UI needs work, that's why I'm not posting the hex-file for direct programming yet as it's not a direct replacement for the original firmware (for instance I have to recompile in order to switch profiles). Feel free to have a look in the GitHub repository!

I'm glad that it works for you. I did have to do a lot of tweaking of the profile to get it just right. Photo of my profile is attached.

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Gerhard56

4 years ago on Introduction

Hi,

maybe it is worth to think about an new Controller instead of a hack. New Controller, USB, so no nasty Buttons, cause the KBD is ... and have easier way to select/create profiles and control the fan/heater ...

With best regards

Gerhard

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ketchopi

4 years ago on Step 2

You made my day, I was ready to give up, it didn't work with lead-free paste.
I have the little one (T-962), and there is no SSR in this model, but the card seems to be the same. I control now the fan as you do, by putting 0V (through a 1k resistor) to the pin #2 of the optocoupler and I read the state of the heater at the same place as you do.


Tests still in progress but turn the fan on at slow speed during the entire process seems to be better than turn it on only when the heater is on (in my case anyway).

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KirAsh4

4 years ago on Introduction

So I made this mod to my T-962 oven and it all works as expected. The problem I'm having is that it's affecting the profile way too much. After all it's sucking in cold air. I've slowed down the fan as much as I could but it's still too much. When the fan is running on PWM, the oven can't reach the required temperature and when it does get within 10 degrees, which automatically shuts off the heating elements and therefore also the fan, the temperature will always overshoot the target. I did a quick plot of a profile on an empty run and you can see it here: http://imgur.com/9SMPlkw (the Heat, Fan, and PWM Fan plots are simply on/off indicators, not like the temperature ones.) You can see, during ramp up, how every time the heating elements shut off (and therefore the fan as well), the temperature will raise and overshoot the target temperature.

So my next step now is trying to figure out a way to not suck in cold air in, but somehow recirculate the hot air that's already in the oven. I'm not sure how well it would work if I close the intake vent during the ramp up, and open it up again during the cool down phase. Maybe I need to find a third fan to install somewhere inside the oven so it only recirculates the hot air that's already inside, as opposed to using the cooling fan to recirculate the air.

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fdavison

4 years ago on Step 2

Thanks for the info about the masking tape. Man, did that stink!