Making your own pcb's.

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victor_pv
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Re: Making your own pcb's.

Post by victor_pv » Mon Nov 06, 2017 6:17 pm

After thinking on the experiences and advice above, this is what I have done so far:

Reflowed 1 board in a skillet. Difficult to keep the heat the same in all parts. Eventually the center of the skillet went up with the thermal expansion, and burnt the center to the board. All the tracks were still fine, and the board is usable. Using sand as recommended by Ray would likely help.
I applied the solder paste manually, quite a lot of time for 0603 components, but doable.

Next I bought this oven from amazon:
https://www.amazon.com/BLACK-DECKER-TO1 ... ction+oven

It's mentioned in several write ups on converting a toaster to a reflow. It's a convection one, with FAN, and 4 heating elements.
Unmodified it works fine for low temp paste (SN PB BI). Much easier than the skillet, solder started to melt about the same time everywhere in the board (10x10 cm board). Heats up fairly quick to 150C, so I actually heated up in phases with the oven controls, and turned it off after the solder paste melted, waited a few seconds and opened the door.

This time I used a stencil I printed several with the 3d printer at 0.2mm layer thickness. Not optimal but works. I am waiting on a laser module to add to the printer for cutting mylar or something similar, then will use that for stencils.

Next, build a reflow controller with a bluepill, a screen and a thermocouple. I have the components but haven't had time to work on it yet.

I plan to use this code, but modified to use the normal Adafruit GFX library, and the stm32 (some timer differences):
https://github.com/dasaki/nanoReflowController

I may eventually modify it to read and save the profiles from an SDcard, or use a touch screen, currently that uses a rotary encoder, and saves to eeprom (which I'm having to adapt to use the stm23 flash instead. Doesn't use much memory, so a bluepill should have enough flash and ram to fit it and leave a couple KB for eeprom emulation.

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RogerClark
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Re: F405 & F411 versions of the BluePill

Post by RogerClark » Fri Dec 01, 2017 12:01 am

Thanks Victor

I think I'll have to dust off my T962 reflow oven and try to fit a fan.

https://www.ebay.com/itm/T-962-Infrared ... 3160938072

Because without a fan its really had to get decent temperature readings. even with 3 probes :-( as I think there are significant hot spots caused by the 2 heating elements which are positioned only an inch or two above the PCB.

I've baulked at doing major surgery on the oven thus far, but I think the T962 is pretty useless without doing some serious changes

The only problem is the construction of the fan as I can't simply make one out of tin plate and solder it together as the solder would melt.

I think I'll probably need to buy some steel bar and cut a thread into the end, then make an aluminium fan wheel and bolt it on the end.

Not sure how I go about making a bearing that will withstand 250 deg, because the fan drive shaft needs to go in through the top of the oven.
Probably some sort of plain bearing is required, or I could get a ball race bearing and run it dry after first somehow getting the grease out.

Any suggestions would be welcomed ... Perhaps we should start a new thread on reflow ovens ...

victor_pv
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Re: F405 & F411 versions of the BluePill

Post by victor_pv » Fri Dec 01, 2017 5:24 am

When you initially told about the mods other people had done to that oven, I stated looking for fans. The only type that I think would stand the head are the stove or oven fans that all metal construction. I remember I found some model in Ebay for a bit cheaper than the majority of them, but even that would cost like 4 times a convection toaster oven. I decide if I was going to do so much surgery to the oven, I would just start with a $30 convection toaster, if it doesn't work I throw it away and start over...
So far I have only reflowed low temp solder, but I have repeated many cycles for lead free solder and the oven has no problem getting to the peak temp. A bit slower than I would like, but not too bad, and I still need to finish adding insulation. It's fun to reflow PCB in a toaster oven :) My wife totally thought it was for the kitchen when it arrived from amazon... :lol:

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Squonk42
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Re: F405 & F411 versions of the BluePi

Post by Squonk42 » Fri Dec 01, 2017 5:51 am

As long as you dont reflow A4-size PCBs and/or fine pitch BGAs, the T962 will do the job, even a toast r oven or a frying pan will do. Here, we have 0603 and 0.5 mm pitch LQFP....

And given that there are only < 50 parts to solder even hand soldering is possible, even if result would not be as pretty. I wonder if it is not as fast as putting solder paste with a serringue and put it into the oven for a single proto!

I have all parts and an early PCBs on their way, some parts I am already receiving, so I should be able to do the assembly before XMas hopefully.

victor_pv
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Re: F405 & F411 versions of the BluePill

Post by victor_pv » Fri Dec 01, 2017 6:01 am

Hand soldering 1 may be just as long as preparing and reflowing 1, but reflowing a panel of 5 or 10 of them I think should be faster than handsoldering the same number.
And for a full panel using a stencil to apply solder paste to the whole panel should cut the time too.
If the BOM is not going to change any more, I'll have a look a order anything I don't have yet (MCUs, usb connector, and SY6280 come to my mind...) do you have links to the parts you ordered?

racemaniac
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Re: F405 & F411 versions of the BluePill

Post by racemaniac » Fri Dec 01, 2017 7:11 am

currently i'm also soldering in a skillet :)
i was pleasantly surprised how well it works with small boards :)
i'm glad i chose to invest in a stencil cutter first so i can quickly apply the solder paste, and even properly solder qfn stm32's, and buying/building an oven is also on my list, but soldering in an old skillet is just working so well that i currently have little motivation to look for something else XD

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Squonk42
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Re: F405 & F411 versions of the BluePill

Post by Squonk42 » Fri Dec 01, 2017 2:43 pm

racemaniac wrote:
Fri Dec 01, 2017 7:11 am
currently i'm also soldering in a skillet :)
i was pleasantly surprised how well it works with small boards :)
i'm glad i chose to invest in a stencil cutter first so i can quickly apply the solder paste, and even properly solder qfn stm32's, and buying/building an oven is also on my list, but soldering in an old skillet is just working so well that i currently have little motivation to look for something else XD
What do you mean by "stencil cutter"?

I am also looking for a cheap way to do pick&place...

victor_pv
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Re: F405 & F411 versions of the BluePill

Post by victor_pv » Fri Dec 01, 2017 3:17 pm

Vacuum pick and place:
https://blog.ohmnilabs.com/diy-vacuum-p ... -and-place

Haven't tried to make one yet, but is on my list.

racemaniac
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Re: F405 & F411 versions of the BluePill

Post by racemaniac » Fri Dec 01, 2017 3:55 pm

Squonk42 wrote:
Fri Dec 01, 2017 2:43 pm
racemaniac wrote:
Fri Dec 01, 2017 7:11 am
currently i'm also soldering in a skillet :)
i was pleasantly surprised how well it works with small boards :)
i'm glad i chose to invest in a stencil cutter first so i can quickly apply the solder paste, and even properly solder qfn stm32's, and buying/building an oven is also on my list, but soldering in an old skillet is just working so well that i currently have little motivation to look for something else XD
What do you mean by "stencil cutter"?

I am also looking for a cheap way to do pick&place...
Stencil cutter: something to create your own solder paste stencils (based on the paste layer gerbers).

I learned about it here: http://dangerousprototypes.com/forum/vi ... =68&t=5341
basically: you buy a silhouette cutting machine (you can probably easily find second hand models, but i bought a new one, A4 size, for 150€)
and someone made a pythonscript to convert gerbers in really precise cutting instructions for that machine. giving you great results from it, directly from gerber files (see the linked forum topic, it's mentioned there in the first page).
as many people recommend, you just buy a bunch of overheadslides (good material, perfect thickness), and then you can start cutting your own dirt cheap solder paste stencils, that work really well for me :).
seeing what a solder paste stencil usually costs, even the cheap ones from china, a 150€ investment and then having cheap custom stencils for whatever i can want (when first working with the QFN chips, i made stencils for only them so i could learn how to work with them properly).

it's maybe not as good as a metal stencil, but for my current needs, i'm *very* happy with this setup :). and btw also invest in high quality solder paste if you want to solder the more difficult ic's :).

zmemw16
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Re: F405 & F411 versions of the BluePill

Post by zmemw16 » Fri Dec 01, 2017 5:22 pm

fan for that T*** oven, anyone thought about using magnetic coupling ?
some pretty strong magnets about these days, less than a 1:1 pickup ratio, i.e. 1:3, 1:4 ratio doesn't really matter as long it moves the air inside.
of course i'm hoping the mounting panel is not steel :-)
stephen

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