so, eurocircuits supply you PCB, you also make stencil with eurocircuits and you mount all parts? is it hard to apply solder paste over stencil? did you actually tried to use oven yet? looks like a good setup...

On Tue, Sep 29, 2015 at 11:31 AM, Luke Kenneth Casson Leighton < lkcl@lkcl.net> wrote:

On Tue, Sep 29, 2015 at 8:31 AM, joem joem@martindale-electric.co.uk wrote:

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On Sun, 2015-09-27 at 16:05 +0100, Luke Kenneth Casson Leighton wrote:

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http://rhombus-tech.net/community_ideas/laptop_15in/news/

CM108AH, and Power ICs, all functional.

Hmm... use the force Luke! An SMT oven is cheap to buy these days..

yes i got the T862A, the one with an 800W pre-heater and a 200W overhead lamp, i can actually see what's going on, keep an eye on the solder as it melts and poke things with a stick if necessary.

...

Making stencils for PCBs to apply solder paste also relatively cheap these days.

yeah i saw that, eurocircuits can do them for $EUR 40 which is a hell of a lot less than $700+ i've previously been quoted.

l.

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joe, how did you get on with an IR oven?

The first few attempts clog up everything. Temperature settings too low or too much solder paste everywhere. The solder paste solvents can evaporate in storage, so mix it with some liquid solder flux to make it flow (and don't breath the solder flux fumes coming out of the oven - take the time to fit proper venting before starting up the oven).

Allow yourself the luxury of destroying 5 boards with cheap chips and components to practice.

After that its regular as clockwork. (Plenty videos on youtube.)

On Tue, Sep 29, 2015 at 10:47 AM, joem joem@martindale-electric.co.uk wrote:

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yes i got the T862A, the one with an 800W pre-heater and a 200W overhead lamp, i can actually see what's going on, keep an eye on the solder as it melts and poke things with a stick if necessary.

I don't dispute the benefits of a T862A, but get oven, destroy a few boards until you got it timed to working 100%, and then its a doddle to plant components, press go, and get working board with near 100% reliability.

for this (first) board i need a slightly different approach, which the T862A suits better. i need to go carefully and slowly, populating only a few components at a time, testing them, inspecting the board, making sure there's no short-circuits (some of the components are 0402), verifying that the circuit is functional by applying power, and correcting it there and then if necessary.

if i were to populate the entire board with components, there would be absolutely no way that i could test individual circuits or components. in some places for example resistors don't measure their actual value because of other components on the board.

i made one mistake by putting in the 3.3v regulator *and* the MOSFETs for the LCD digital circuit. the 3.3v regulator circuit was fine, but the LCD digital 3.3v supply circuit wasn't. so i dismantled pretty much the entire 3.3v regulator circuit, had to cut PCB power line tracks, and generally messed up the board, taking over 2 hours to track down what was wrong.

if i had put down only the 3.3v regulator and then tested that, i wouldn't have had to remove any of its components.

now multiply that scenario up for an entire board and it's easy to work out why i'm doing this a bit at a time.

so i'm using the T862A as a PCB development tool, not a PCB *production* tool. if i was doing small runs of PCB production, where i was absolutely 100% confident that the circuit was proven, correct, and functional, *then* yes absolutely i would get one of the T962 ovens.

l.

On Tue, Sep 29, 2015 at 11:39 AM, joem joem@martindale-electric.co.uk wrote:

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so i'm using the T862A as a PCB development tool

No. Nurse the oven as your tool.

remember, joe, you've done this a _lot_, so have much more confidence in your abilities, as well as, from experience, a much higher anticipated success rate. i had no idea what i was doing, so i needed something which i could monitor closely and much quicker (like... immediate), on a much smaller area.

so: i can't see inside the oven with the door closed, can i? that's what i like about the one with the lamp: it focusses the IR on a small area (about 5cm in diameter), i can get tweezers in underneath it and remove components (or adjust their positions), i can watch the solder actually melting, i can actually *see* the point when the components flow into the solder, i can get solder in with a bit of solder paste on the end to encourage the solder on the board to melt...

pluuuus, i can put only a tiny amount of solder paste down, which is tolerable with the windows open.

you can't do _any_ of those things with an oven: it heats up the entire board, it's an enclosed space, you have to heat up *all* the components including all the ones that you previously placed, it takes a long time to warm up and cool down...

so you *have* to do all the components (or risk re-heating all of them). whereas i'm safely doing 5-10 components at a time, confident that because the tested ones are in another area away from the lamp, they won't get moved, overheated or (in the case of the TSSOP-56) warped beyond useability.

when all the components i've put down are clearly visibly in full solder-contact with the board, i can shut down the lamp immediately. sometimes i've managed to get components soldered in about... 4 to 5 minutes. removing components (including SOT-23s and TSOP-8s) can be as little as 3-4 minutes. can you do that with an oven? no.... you can't see inside it, clearly, so you have to play it safe and let it heat up on a full cycle, which is what... 10 to 15 minutes at a time?

you said it yourself: you destroyed several boards, first time you used the oven. i only destroyed one, and it was the first test board i'd ever done, it was only 1in x 0.5in in size (the fibreglass actually delaminated). i learned from that, and haven't damaged the laptop PCB at all. i've only destroyed around 3 components in total, one was the TSSOP-56, it actually curled up at one end due to uneven heat distribution and i wasn't watching the lamp's temperature sensor closely enough. so i'm leaving its replacement until last.

now, the down-side is: it's taken 2-3 weeks of about 1 to 2 hours a day to put down all the components... and there's only about 120 maybe 150 components. that's *ridiculously* slow.

...but i don't care if it's slow: this is my first PCB since.. since.... making illegal FM transmitters back in 1983 from "the anarchist's handbook". i've done the "pay someone else to design PCBs" thing - that didn't work out. even paying someone else to assemble PCBs is relatively pricey (if you get it wrong more than zero times).

so i am simplifying the task to one which, with my skill set, stands an above-average chance of success and/or is a much lower iterative cost.

Its more safer and use as many times as you want. (Some items such as LEDs won't survive re-use too many times - but they are cheap to replace.)

found that out already :) one of the other components i destroyed was an 0805 LED - i hand-soldered the next one...

l.