Preheating with the T8280

[edgelog]

I had a lot of problems, actually total fail, trying to solder a new display connector onto a Macbook Pro main board. I also had to replace a resistor, really hard. The ground plane on these boards suck all the heat away. I've tried with all manners of tips for the Ersa iCon i-Tool, which in itself should be powerful enough under other circumstances. I did get the old display connector removed using an Atten 858D+.

So I got me a Puhui T-8280 from the UK at around 110 pounds total (currency, not weight). The advantage, except for the price, is the size. It can easily heat an entire Macbook Pro logic board.

The manual says to set it to 100-120 C for Pb/Sn solder, 120-140 for unleaded. The thermometer on the device is touching the heating plate from above. With this arrangement, setting the T8280 to 120 C, the top of a test board barely reached 50 C, so I bent up the thermometer holder a bit until the tip of the thermometer rested a mm or so above the plate (see image). That improved things somewhat. However, the top of the board never gets much above 68 C, and the bottom of the board reaches around 85 C after about 15 minutes on the 120 C setting.

When setting the device to 150 C, the top of the board reaches around 88 C after 15-20 minutes, the bottom gets to 105-107 in the same interval.

I've attached the graphs of these two experiments, each including 20 minutes of active heating, and another 20 minutes of the device cooling off with the small switch set to off and the mains switch still on. (In the first graph, I didn't measure the bottom temp from the start.)

My question now is this: the manual says to set the T8280 to 140 C for leadfree PCBs, but that results in a board at effectively 90-105 C. For effective soldering, shouldn't the board itself, at least the bottom of it, reach 140 C? Which would presumably mean that I should set the T8280 to 200 C or more to get to that level. I'd appreciate some opinions about this before I set out on a quest to set logic boards on fire.

And, incidentally, now I see the point of preheaters having a temperature probe you can attach to the board. Ersa does that, I think. OTOH, their preheaters cost 1-3k euro... Maybe I should move the fixed probe on the T8280 and make it attach to the board? Anyone done that here?

BTW, they included a long and narrow sticker made of foil, see the last image. I can find no explanation what it's for. Does anyone know?

[cdev]

So, you are supposed to work on the board with other tools while it is being preheated to reduce the extra heat which needs to be applied?

[edgelog]

So, you are supposed to work on the board with other tools while it is being preheated to reduce the extra heat which needs to be applied?

Yes.

[cdev]

So I just got one too, except mine uses a big aluminum slab and is supposed to go up to 350 C.

I have not had the time to try it out yet.

[edgelog]

So I just got one too, except mine uses a big aluminum slab and is supposed to go up to 350 C.

I have not had the time to try it out yet.

When you do, take a few pics and upload. I'm curious how that works. Do you just plop down the board on the aluminum slab or is it suspended above it?

[cdev]

Put them right on the slab.

Solder does not stick to it at all.

I got a "946C" - it seems to be popular. Its a blue square metal box with the hot plate occupying almost its entire top, Its around 20 cm square. (see photo)

[adamistr0]

Hi, sorry to revive this thred, but I have bought this exact preheater and have the same problem with low temperatures
Have you fixed it somehow? I bent the probe further from heater, but I think that best would be external probe.

[edgelog]

Hi, sorry to revive this thred, but I have bought this exact preheater and have the same problem with low temperatures
Have you fixed it somehow? I bent the probe further from heater, but I think that best would be external probe.

No, I have only used the heater occasionally since then. I have, though, used it in conjunction with a hot air gun. The reasoning being that you need less hot air if the board is preheated a bit, and you reduce thermal stress on the board.

I tried reflowing a bad GPU on a Macbook motherboard and completely failed. The whole sad story can be seen and read here:

https://www.ursecta.com/2019/03/23/reflowing-a-macbook-pro-gpu-to-no-avail/

[masterx81]

Recently i've bought the same preheat station, but i've not had occasion to use it.
In any case i've modified it a little bit allowing to turn off one of the 2 heaters (when doing smaller boards) and i've put an heat insulating matt on the sides for maintain the heat under the board. From previous experiences i know that the board must be at 100-150c before applying the hot air. 50c is absolutely not enough.
I agree that the thermocouple must be external on the board, and not over the heating elements. It's a normal type k, so would be quite easy to mod

[masterx81]

And this is what i've done.
I've added also a support for the heat gun, it not help much with big packages as you have to move around the perimeter of the package, but with smaller packeges have one hand free is nice.
The insulating matt help keeping the heat under the board (less heat directed to the hands) so that the board temp and the heater temp must be quite similar.
Now i need to find a way to put an external type k and have the ability to switch between thermocouples.

[zero9]

What is the issue? of course top side will be colder than bottom where the sensor is located.
I have the same unit. Good for its price and cant complain. I use 150 degree Celsius bottom temperature. When its reached, temperature usually stays about ~110-115 degrees at the top of the pcb, it may vary depending on pcb thickness, time etc..
It still a preheater!

[colorado.rob]

I just got one of these and have been doing rework on a number of boards.  For the price, it's quite a bargain.  I have not have any issues with it so far.

I have a reflow oven and am quite familiar with the reflow profiles needed for my board panels and solder paste.  Most reflow profiles for lead-free solder have the boards soak at 180C for a while before taking them up to a brief excursion to 230C for reflow.  Knowing this, I set the T-8280 for 180C and let the boards heat up for 4-5 minutes before putting the hot air to it.  I was removing some fairly large wireless modules.  I had to heat a rather large area of the board.  The modules have metal caps soldered on them and I did not want these coming off the module PCB.  That meant I had to be careful to heat the PCB and not the module itself.  It generally took 30-60 seconds or so going around the module with the hot air to reflow all of the  pads.  I was reflowing panels of 10 boards and these took about about 15 minutes each.

I can fit two panels on the heater at a time.  I can be pre-heating a panel on the back plate while working on a panel near the front.  I had a short [dis]assembly line going at one point.

One thing I am having an issue with is that I don't seem to have enough power for both the pre-heater and my hot-air soldering station.  It sounded like the soldering station was struggling for power when the preheater came on to maintain temperature.  I have a 20A (110V) circuit and it seems that I am on the cusp of what it can handle.  I was somewhat expecting a breaker to blow while working on the boards.

I do need to open it up and see whether it is properly grounded.  And that fan has the most annoying high-pitch sound I think I have ever encountered in a fan.  I have a proper power cable on order.

Does anyone have a recommendation for a replacement fan for this model?

[nwind]

Does anyone have a recommendation for a replacement fan for this model?

Noctua NF-A4x20 FLX, Premium Quiet Fan

https://www.amazon.com/gp/product/B072JK9GX6/ref=ox_sc_act_title_1?smid=A1Z5H6ZGWCMTNX&psc=1

[cdev]

The preheater shown in the earlier photo is much nicer than the one I have which is just a simple blue box with a PID unit in it and a square heating plat on top and digital control. my unit can get hot enough to melt solder easily though although now I use it below the lead melting point to lower the time needed to solder. It takes too long to cool down to safely use it for a solder melting device, it would ruin my vias if it kept things too hot too long. (thanks Blueskull for that pointer!)

My unit does not have a fan at all.

It was cheap, and it works.

[cdev]

I don't have this unit - The one I have is much plainer and doesn't have the curtains/heat container or rails. And I spent I think around $45 for mine, if that. I'm notoriously cheap and poor.

Recently i've bought the same preheat station, but i've not had occasion to use it.
In any case i've modified it a little bit allowing to turn off one of the 2 heaters (when doing smaller boards) and i've put an heat insulating matt on the sides for maintain the heat under the board. From previous experiences i know that the board must be at 100-150c before applying the hot air. 50c is absolutely not enough.
I agree that the thermocouple must be external on the board, and not over the heating elements. It's a normal type k, so would be quite easy to mod

[cdev]

I have two little tiny bimetal thermometers (old school) made completely of metal, each around the size of a small coin that respond instantly, I used them in the past with a small skillet on my gas stove to reflow solder. That works. No electronics, and totally analog. They thermometers can stand the heat, although the paint on their dials is coming off. They have a little red arm to reference any changes against.

My friend uses an iron clamped upside down and leveled precisely with a spirit level to reflow PCBS.  He did this to produce a very high quality commercial product he was making - he swore by it.

The tiny thermometersare made by a California company and are still sold but are ridiculously expensive. You might be able to make one yourself. Digital made with a PID unit would be better and easy to automate. I like being right there and seeing the arm move with temperature. Because the thermometer has barely any mass it moves very quickly.