Mini or smallest board preheater - Page 1
Forum section: electronics / general

author: silviasol
author_rank: Regular Contributor
timestamp: July 03, 2016, 03:05:34 pm
content: You guys seem to know everything based on the few questions I have asked, was hoping someone would know what is needed to make a very small board preheater. I work on these small 40 by 80mm boards and it makes soldering a whole lot easier having the board preheated but a pain working over the heat of my large board preheater since it takes almost 45 minutes soldering to do all the tiny chips. I figure it will only require some simple components, say some heating wire and high temp epoxy connected to a copper plate? Just have no idea about the wiring size, type... and circuitry needed to adjust the heating part. Just need it to get to about 100-125c. Any idea's?

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 03, 2016, 03:15:54 pm
content: Something's wrong if it takes 45 minutes to assemble a board like that.

author: Howardlong
author_rank: Super Contributor
timestamp: July 03, 2016, 03:21:59 pm
content: Is this a one off or a production run (how many?), or is it rework? Paste? And if so are you using a stencil? Is the board double sided or mutilayer? It looks like it has a flooded groundplane.Sorry for all the questions, it will help answer your question though.In the meantime, I do a lot of work on similar sized boards, multilayer with flooded groundplanes and parts on both sides. For one offs I reflow the QFNs and BGAs with a hot air iron, but it's good old fashioned hand soldering for everything else. For assembling more than a very few, I stencil and paste, and use a toaster oven. For rework, I've tried small preheaters, but I find them more trouble than they're worth.

author: SeanB
author_rank: Super Contributor
timestamp: July 03, 2016, 03:24:36 pm
content: Get a local hackerspace to machine a block of aluminium 50x100x40mm to size, and to drill 2 holes in the side, one of 6mm diameter and another of 16mm diameter. Then buy a pt100 sensor with a 6mm sheath, a 200W-300W 115VAC tubular heater ( find one 100mm long and 16mm diameter, a relatively common size for these elements) and a simple pt100 type industrial controller with PID off eBay, along with a DIN case to suit. Then wire up and you have a small adjustable preheater, good for almost any temperature ( once you press autotune once) from 100 to 160C which fits the board you are working on. Ground the block to the mains earth, otherwise you will find any leakage killing you and your parts.Nicening it up use a wooden cutting board 40mm thick on either side to rest your hands, and put a heat resistant plate under it to keep it from cooking your worktop.

author: silviasol
author_rank: Regular Contributor
timestamp: July 03, 2016, 08:15:11 pm
content: Quote from: Howardlong on July 03, 2016, 03:21:59 pmIt is multi layer double sided board. I do them about 5 at a time with my current preheater. I have a stencil but with a preheater I just use hot air and add each component one by one, that has been easiest for me. It is an open source esc, details about it are at vedder.seThe pinned chips that are on the board I do by hand. I found that aligning the pins perfectly with the traces using flux and the right tip gets all those pins done in minutes. Hate doing it without the board preheated. On a cold board would it be possible to cause damage to the chips from thermal shock from soldering them or are they capable of handling the heat?Quote from: NiHaoMike on July 03, 2016, 03:15:54 pmYes I timed myself to finish one board and it was 45 minutes, the components are so tiny and I keep messing up aligning them over the heater. Which is why I want a small heater to have my hands more free to work on it. Unless you thought that was the finished board, a complete board is below.Quote from: SeanB on July 03, 2016, 03:24:36 pmI was hoping to make something more low voltage, not sure I would trust myself making something with 115v. Thanks though, I will look into it.

author: janoc
author_rank: Super Contributor
timestamp: July 03, 2016, 09:54:39 pm
content: You may like these:http://hackaday.com/2016/04/01/tiny-hotplate-isnt-overkill/http://hackaday.com/2016/05/21/ptc-heaters-for-reflow-soldering/The PTC heaters can be had really inexpensively online and they self-regulate their temperature - so just get one for your desired temperature and you are set.

author: uncle_bob
author_rank: Unknown
timestamp: July 03, 2016, 10:41:31 pm
content: HiThere are a lot of ways to do a pc board layout wise. In many ways the decisions you make in layout dictate how hard or easy it will be to assemble the board. One way to assemble a board like that is to do it multi pass. You do the SMT parts with stenciled solder and a reflow oven. You then do the through hole stuff by hand. The last step is to do the wires, also by hand. If the layout / design is done with this in mind, you don't do any pre-heat at all .....Bob

author: nanofrog
author_rank: Super Contributor
timestamp: July 04, 2016, 04:50:14 am
content: Quote from: silviasol on July 03, 2016, 08:15:11 pmThey're tougher than you'd think (made to tolerate reflow ovens), but you still want to get off of it quickly when doing it by hand as the pads & traces are more delicate than the IC as a general rule.Quote from: silviasol on July 03, 2016, 08:15:11 pmLook forMetal Ceramic Heating elementson eBay or similar (aka MCH element). BTW, this is the same thing used in the first linkjanocposted.They don't require mains (i.e. 12V or 24V), are small so can meet your size requirements, and are inexpensive. For example, you could opt for a couple of 30mm rounds to preheat the entire board. Cost wise, a 30mm round 24V & 400C unit goes for $12.60 (here), and the 12V version is a little less expensive (the higher voltage units should heat up a bit quicker).Wouldn't be too expensive, complex, or time consuming to knock something together using these IMHO.

author: Philfreeze
author_rank: Regular Contributor
timestamp: July 04, 2016, 09:06:19 am
content: Buy a silicon heating pad (example:http://uk.rs-online.com/web/p/silicone-heater-mats/0245528/) and glue it onto some kind of heat isolation (you should be able to get something like that in a local store I assume). Then just put some kind of temperature sensor between these two and make a small circuitry with TRIACs (if you want to go for the high power 110/230VAC variant) or with MOSFETS (12/24V variant). You just have to turn the MOSFET on and off at two temperature points (simple two point regulator). This can be done pretty easily even without microcontroller if you don't want to use one (voltage divider, amplifier and schmitt trigger).A big plus of these silicon heating pad is that they aren't rigid which makes it a whole lot easier to attach them to something.If you want to adjust the temperature you can also add an offset in the amplifier stage and put a potentiometer in the circuit. Then you can adjust the temperature.

author: plazma
author_rank: Frequent Contributor
timestamp: July 04, 2016, 09:47:32 am
content: Familiar PCB. I had to replace the driver IC to one board. The vias were very easily damaged.I have been looking for a flat and compact preheater. I need to check the parts suggested in this thread. I was thinking of making a quick'n'dirty version out of a strip vero board.

author: Howardlong
author_rank: Super Contributor
timestamp: July 04, 2016, 05:22:10 pm
content: So is is the one I have:http://www.ebay.co.uk/itm/Tenma-21-10135-Mini-Smd-Preheater-100-350-Deg-C-/261733068963The reason I don't get on with it for rework is simply that it's slower than without. The magnetic jig supplied seems a good idea but in practice was almost useless.Now I see it's pupulated on both sides, I can see why you haven't used an oven. I can also see why it would take 45 mins/board. There are some rather heavy parts on both sides which makes oven soldering more difficult: it's not a bad idea when designing boards to have all the heavy parts on one side, and do that side last. So an alternative, you could go fo a hybrid approach, place all the lighter bottom side parts, looks about 80% of them, oven, place the entire top side, oven again. Then manually solder the remaining heavy bottom parts.

author: uncle_bob
author_rank: Unknown
timestamp: July 04, 2016, 05:32:01 pm
content: Quote from: Howardlong on July 04, 2016, 05:22:10 pmHiThe same "heavy parts" issue gets you when manually soldering the board and running pre-heat as running an oven. Solder does not go instantly from a solid to a liquid. When it is in a plastic state you can easily disturb a solder joint. Doing the big fat parts on top is almost guaranteed to get the identical parts on the other side moving around ....Bob

author: nanofrog
author_rank: Super Contributor
timestamp: July 04, 2016, 06:50:04 pm
content: Quote from: Howardlong on July 04, 2016, 05:22:10 pmI've the same preheater, and the board holding jigs are definitely a complete joke. I use aPanavise 315which does a much better job, and the unit itself does work. I'm certain it has saved me some aggravation & prevented me from lifting pads.You might want to consider a324 Electronic Work Centre(has the 315 head + all the bits you need) or even one or two Hakko Omnivise's (here).Quote from: uncle_bob on July 04, 2016, 05:32:01 pmHave you tried a eutectic alloy such as 63/37?As it doesn't have a plastic state, it's more forgiving than say 60/40, and allows you to work a bit quicker too.

author: kripton2035
author_rank: Super Contributor
timestamp: July 04, 2016, 06:56:27 pm
content: I have a Yihue 853AA kind same model of heater/preheater and I can confirm it works quite well to preheat the boardand I can confirm the board jig is a big ... joke !

author: uncle_bob
author_rank: Unknown
timestamp: July 04, 2016, 07:00:50 pm
content: Quote from: nanofrog on July 04, 2016, 06:50:04 pm

author: bitslice
author_rank: Frequent Contributor
timestamp: July 04, 2016, 07:36:01 pm
content: One of the reprap heater beds should work, they get to around 100degC,around £15, ebayhttp://reprap.org/wiki/PCB_Heatbed

author: nanofrog
author_rank: Super Contributor
timestamp: July 04, 2016, 07:46:28 pm
content: Quote from: uncle_bob on July 04, 2016, 07:00:50 pmTrue. As fracturing wasn't mentioned, I inferred the alloy used was non-eutectic.FWIW, I do find the eutectic stuff is a bit easier in regard to bad joints, as I don't have to wait so long for it to solidify. But any alloy can result in bad joints if disturbed during solidification.In the particular case of components on both sides, it's certainly a lot trickier, even when done right/all the stars & planets properly align. Enough so that using adhesives on parts during placement may even have to be considered along with everything else.Personally I don't have an oven, so the choices for me are a tad more limited (iron, hot air, & preheater). Makes it easier for me in some ways, with the trade-off being it consumes more time.

author: D3f1ant
author_rank: Frequent Contributor
timestamp: July 04, 2016, 07:56:41 pm
content: I also use one of those cheap tenma preheaters for rework and even occasionally for reflowing small prototypes. They are remarkably effective especially for the price, I got mine for us$50 in an E14 sale. The magnetic holder things it came with are completely useless and went in the bin on the first day. Hakko omni vices are good, very heavy/secure so you probably only need one most of the time.

author: silviasol
author_rank: Regular Contributor
timestamp: July 07, 2016, 05:18:05 pm
content: Quote from: bitslice on July 04, 2016, 07:36:01 pmThat is really interesting. Do you just hook a 24v power supply up to it? How does it work?

author: janoc
author_rank: Super Contributor
timestamp: July 07, 2016, 09:45:21 pm
content: Quote from: silviasol on July 07, 2016, 05:18:05 pmActually I wouldn't recommend that. I have a 3D printer that uses one of these. It is nothing else but a piece of FR4 with a spiral trace etched into it and powered from a 12V power supply (usually a PC ATX supply). Some of these can use 24V but not all.The plate doesn't quite get to 100C in most cases - e.g. mine takes about 10 minutes to warm up and doesn't reach more than about 80C, even though the printer claims it is at 100C - they are not super accurate unless you carefully calibrate the thermistor. The surface is not heating up evenly neither, you will have hot spots. These beds also don't come with any regulation, so you would need to add a PID controller. That is normally part of the 3D printer electronics.If you really want cheap, go with the PTC heater I have posted earlier. That is self regulating and the price is about the same as the printer bed. And it is far less flimsy - if you want to solder on it, the PCB of the bed will most likely delaminate after a while. They are not made to withstand high temperatures.

author: bitslice
author_rank: Frequent Contributor
timestamp: July 07, 2016, 09:55:46 pm
content: Quote from: janoc on July 07, 2016, 09:45:21 pmI didn't realise they were self regulating, thanks for the usage feedback

author: janoc
author_rank: Super Contributor
timestamp: July 08, 2016, 07:21:17 pm
content: Quote from: bitslice on July 07, 2016, 09:55:46 pmWelcome. PTC stands for "positive temperature coefficient" - it is thermistor with resistance increasing with temperature, usually sharply at a certain temperature. So it reaches equilibrium because the increasing resistance limits the current flowing and thus temperature of the heater.

author: silviasol
author_rank: Regular Contributor
timestamp: July 09, 2016, 07:18:04 pm
content: Yea PTC definitely seems the way to go. I am looking at one that is 24v 10w and 150c. I see others that have higher watts, 20-50, and have the same 150c temp. What does the watts do, is a low watt enough for just preheating a small board. I assume they use these for water heaters mainly so I would think more watts heats up larger water tanks?

author: janoc
author_rank: Super Contributor
timestamp: July 09, 2016, 11:20:08 pm
content: I would assume more watts = faster heating up, everything else being equal.

author: nanofrog
author_rank: Super Contributor
timestamp: July 10, 2016, 02:40:34 am
content: Quote from: janoc on July 09, 2016, 11:20:08 pmConsider the following...If the heating element of a given iron or cartridge tip is designed for say 70W, and is then attached to a power unit that can deliver 200W, it's heat up time won't change since the element resistance hasn't changed. Change the heating element to something that can take 200W however (lower resistance), and then there's the potential for it to heat up faster (would need the set temp & tip shape to be the same vs. the 70W version).

author: janoc
author_rank: Super Contributor
timestamp: July 10, 2016, 03:08:29 pm
content: Quote from: nanofrog on July 10, 2016, 02:40:34 amWhich is a longwinded way to say exactly the same thing as I did ...

author: silviasol
author_rank: Regular Contributor
timestamp: July 12, 2016, 08:34:32 am
content: I am looking one that is 120v 70w 130c, 130c is a perfect temp. I would assume to just wire it directly to a 120v plug, or would I fry the thing up that way. Seems so much voltage for a tiny thing.http://www.ebay.com/itm/152138736460

author: janoc
author_rank: Super Contributor
timestamp: July 12, 2016, 09:24:40 pm
content: Quote from: silviasol on July 12, 2016, 08:34:32 amI think those are designed to be connected to mains directly. The resistance goes up and keeps the current in check, so you shouldn't be able to fry it unless it is faulty somehow. Perhaps use a variac for a test?

author: silviasol
author_rank: Regular Contributor
timestamp: July 15, 2016, 10:38:21 pm
content: Quote from: janoc on July 12, 2016, 09:24:40 pmOk I bought two of them. If I hook two up in parallel to the plug would that damage them? I plan on bolting them to a 6" x 3" metal sheet with 1" legs, should work out well.

author: janoc
author_rank: Super Contributor
timestamp: July 16, 2016, 12:51:00 pm
content: Don't see why that should damage them (it is basically a big resistor), but I have never used these. Just make sure you have sufficiently rated plug/wiring/mains circuit for the current the heaters need. Also make sure to use a proper grounding and connect all exposed metal bits to the ground.