Simple small IR preheater using 12V halogen - Page 1
Forum section: electronics / projects

author: cybermaus
author_rank: Frequent Contributor
timestamp: September 16, 2021, 11:17:02 am
content: So recently I have had to (wanted to) replace some memory on Ubiquity M2's, which went well, till I found out the newer ones use BGA84 memory.With practice (on old junk boards) I managed to do this, without loosing any devices, but it sure did bring to me the realisation pre-heaters are important.To get sufficient heat to flow *through* the chip, I had to set my Air to 380C, and it still took way to long to my liking.So, I build a small local preheater based on a old 12V GU5.3 / MR16 Halogen bulb.And I have to say..it works *amazingly well*I was able to replace the same memory now with only 280C air setting, and managed to properly reflow a larger BGA CPU with 300C(and with proper reflow I mean, I got the CPU to "dance", and it still worked afterward)In fact, this small and easy to grab setup, super easy to use on my normal workbench, I may now use for normal SOIC, fet's, resistors and such stuff as well.Maybe just put the Halgen on only 10V or so.And it is light and quick. The 50W radiated to the board is very fast, I imagine a large pre-heater needs to first heat up itself.The "blue thing" is my normal "board holder". I have been using that for a while already.It has some magnetic stands with rubber grommets to hold the board edgesIt does not look much, just a piece of iron I grabbed from the garage, I was planning to powdercoat it, but that has not happened yet.But you know, a proper heavy piece of iron with magnet stands is already very useful for stable work-holding.I am petty sure it works better then the tiny magnet stand things you can get from eBay.So I put an extra hole in the holder for the Halogen bulb, and the pcb quickly goes to 90C, then increasingly slower goes to 120C or even 140C if you go for a coffee first.Also, the bottom side of the board is not that much hotter then the top side, as shown from the 2nd IR imageI realise this is looks terribly shoddy, and no professional would be caught dead with my self-made blue "workholder" and self made "pre-heater" but I tell you, they work amazingly well, and I can advise it to other low-budget hobbyists.In fact I may eventually buy a proper pre-heater, but for quick small solder jobs on fets and other ground-plane-connected stuff, this may remain a goto solution as it is part of my normal workholder setup.

author: Cerebus
author_rank: Super Contributor
timestamp: September 16, 2021, 02:52:40 pm
content: Quote from: cybermaus on September 16, 2021, 11:17:02 amIt doesn't look pretty, but a pretty tidied up version of the same probably wouldn't look out of place as a bit of professional kit.One advantage I can see is that it provides reasonably localised heat and it's easy to see where you're putting the heat. I might well give it a spin myself,ifI can find any incandescent lamps in this age where it's practically a crime to sell them.

author: Gyro
author_rank: Super Contributor
timestamp: September 16, 2021, 06:03:23 pm
content: If you want an even more compact IR source, an H4 Halogen headlamp bulb works well. The dipped beam filament has an integral side firing reflector. The mounting flange is spot welded onto the barrel and easy to remove. You can then mount it in a fixed horizontal metal tube and move the board around underneath it.Sadly, it's inevitably the dipped beam filament that fails in old lamps, leaving a perfectly good, but less useful main beam filament. At least they're cheap anyway.P.S. Don't forget your sunglasses!

author: cybermaus
author_rank: Frequent Contributor
timestamp: September 16, 2021, 06:19:45 pm
content: Quote from: Cerebus on September 16, 2021, 02:52:40 pmStill planning to powdercoat. Waiting to have some more stuff to send to powdercoat in a batch.I prefer powder-coating rather then painting, as it is slightly thicker, giving the magnets a bit of a dampening when they land.If I do not place them softly, the very brittle magnets sometimes chip.Quote from: Cerebus on September 16, 2021, 02:52:40 pmI had the same thought, wondering ifI should get a spare already..While searching, I found there also exists, and they are even more easily to get, similarform factor GZ6.35that are used in video projectors. I briefly thought that was even better, because they are 100W.Until I saw their lifespan: one had 40 hours, another 50 hours.So I'll stick to stocking up a pair of 5000 hour GU5.3. Should last me a lifetimeQuote from: Gyro on September 16, 2021, 06:03:23 pmYeah, not even remotely possible to forget that.But seriously, lighting from the bottom, all light is shielded by the PCB. Very little comes through, usually those boards have layers of ground, but I do see some traces and vias.But I guess if I have to work toward the side of the board, I may have to put some extra tin-foil. Still, I repeat, not even remotely possible to forget your sunglasses.

author: Ian.M
author_rank: Super Contributor
timestamp: September 16, 2021, 06:20:41 pm
content: I described my 50W MR16 halogen board preheater here:https://www.eevblog.com/forum/manufacture/small-bottom-heater-for-rework-and-reflow/msg3427730/#msg3427730Its got a wallboard work platform with the bulb mounted in a tomato puree can bonded into a hole in the middle of the wallboard so the bulb glass is flush with the work platform, a dimmable 'transformer' and a dimmer for easy power control.

author: cybermaus
author_rank: Frequent Contributor
timestamp: September 16, 2021, 06:27:59 pm
content: Quote from: Ian.M on September 16, 2021, 06:20:41 pmDamn. No good idea I can have and someone already did it.And I even searched youtube while I was doing this.And then famous John Ward even, I missed this video.Anyway, interesting remark about "designed to radiate to the back".I did not have issues with that, but will test to see. Maybe I was lucky to have one of those aluminium ones.Edit: Osram specs confirm John Ward: Their marketing advertise their "Alu" models to radiate heat to the front. And their non "Alu" models are reducing the heat send to the front, meaning they keep them in the back.Mine is a non-alu Philips Dichroic one, but it seems not to be a problem on my workbenchHowever, I will make sure the spares I buy are Aluminium. Even though they aretwice as expensive.Maybe I can then even turn down the voltage a bit to reach the same temperature.

author: Ian.M
author_rank: Super Contributor
timestamp: September 16, 2021, 07:50:11 pm
content: I claim no credit for originality as I was inspired byhttps://hackaday.com/2016/12/23/halogen-lamp-abused-for-desoldering/+ various discussions here. My version can easily bring an area of the board up to Pb-free reflow temperatures even without top heat and with a ground planeThe aluminum foil supplementary heat reflector kapton taped direct to the dichroic bulb's reflector works well enough. The sides of the puree can stay reasonably cool, or at least not hot enough to be hazardous.

author: cybermaus
author_rank: Frequent Contributor
timestamp: September 17, 2021, 01:10:01 am
content: Indeed, with alu-foil (shiny side in) it goes up faster (maybe even too fast) and reaches up to 185C.Not quite flow temp like you, but higher then before, the alu tape clearly helps.So why does yours go higher. Are you feeding it DC or AC? I think you mentioned transformer and dimmer?I feed it strict and exact 12.5V DC from my lab supply, it reaches 4.24A with 185C after some wait.Waiting really long, at 190 it starts making cracking noises. By 205C they have stopped.I never seen it above 205, not even after half an hour.The PCB should be able to accept full reflow in an oven, yet it starts to make these crackling noises.I think the radiation may affect darker spots on the PCB more then lighter spots.And any black components placed on the back would be worse (this board does not have any)Not sure how/why you get it to full reflow, but I think for rework, I will stick to 140~150C and some light hot air.EDIT:It may not have been the PCB but the PVC standoff ring that was doing the crackling. See imageBut no matter, I plan to not go beyond 150C anyway, remade the ring.

author: Kerlin
author_rank: Regular Contributor
timestamp: September 17, 2021, 01:39:35 am
content: I came across an expensive commercial pre-heater unit that increased the heat slowly, over 1.5 hours.They said this is to help reduce the temperature difference between the PCB base material and the copper tracks, the temperature difference can cause the track adhesive to crack weakening the adhesive.I use this method to heat it and then use conventional soldering, de-soldering and heat gun methods when doing repairs.Sounds like a good idea and I it did found in practice it did work better, in particular on expensive Teflon RF boards for military and avionics use.Might be an idea to get an MCU to slowly turn it up.I normally simply use a variable power supply and 10 or 20 watt resistor under the board , feel it every 15 mins and turn it up, works well and I prefer to personally supervise the process, rather than use an auto unit and come back later and see what happened.That's why I am a better cook than my wife I stay there and manage the cooking process, she leaves and comes back later to see what happened.Besides my repairs are expensive so they must be spot on. The company once had a compliant that the board worked but I had done nothing to it.The company owner was over the moon cause the customer looked hard but couldn't even see where the board had been repaired.So it must work OK.

author: Ian.M
author_rank: Super Contributor
timestamp: September 17, 2021, 01:45:56 am
content: It may be due to my construction with the rim of the tomato puree can flush with the wallboard and the face of the bulb filling nearly the entire opening. There isn't a lot of air circulation with a board over it so there isn't much heat loss except from top-side convection. Also the 'transformer' (actually an high frequency AC output SMPSU originally specifically sold for halogen lighting applications) is (IIRC) rated for 100W of bulbs so may be running a single 50W bulb a little hot when the dimmer feeding it is at max.I certainly wouldn't advocate routinely reflowing just by IR from underneath as getting enough heat top-side through the board is going to be pretty harsh on the board itself and you certainly wouldn't want to cook it for longer than five minutes from cold. In the oven it gets heat from both sides which is less stress on the laminate and also less time to reach temperature. For small enough boards to fit on the lamp face glass it would closely resemble skillet reflow, and should work well enough with Sn/Pb or other lower temperature solder paste, though a Pyrex beaker or similar as a cover would be helpful to reduce convection cooling while still permitting observation.

author: cybermaus
author_rank: Frequent Contributor
timestamp: September 17, 2021, 01:59:04 am
content: Yes, I am now trying to do too much.Stretch it beyond what I meant it to do.Going back to my original purpose: Repair and reflow BGACompared to using only air, it works really well.Something everyone who already has a pre-heater knows already.And as small and integrated as it is into my normal work-holder, I will even use it for any other component I would grab my air for. Just don't push it above 140~150.That is what really makes this a winner in my eyes. It's always there, ready to go.

author: cybermaus
author_rank: Frequent Contributor
timestamp: September 18, 2021, 12:55:26 am
content: I made a stand, as inspired by Ian, made from a tomato puree tin can.So I can can also use stand alone.Or like in the shown image, use it when the PCB hangs over the side(still quite stable like that, as my work-holder is a pretty heavy piece of iron)I think the reused tin-can stand really complement the look of the scrap-iron work-holder