[chbot] SMD experiment #1

[Next Kiwi]

G'day Chris

I am using a toaster oven successfully here, I even do the odd BGA. We have 
a compressed air solder paste dispenser which is probably the key to getting 
good control of the paste. Its not great but we get good boards. I have 
found the most valuable tool is "flux paste". I use this to clean up the 
board afterwards. Flux paste is magic stuff. It is a must if you are doing 
MLP or QFN packages.

You did the right thing by putting the temperature sensor very close to the 
board as the temperature around the oven can vary.

To clean the flux off I use electrolube FLU
http://images.google.co.nz/images?hl=en&q=electrolube%20FLU&um=1&ie=UTF-8&sa=N&tab=wi

Cheers
Keith


----- Original Message ----- 
From: "Chris Hellyar" <chris at trash.co.nz>
To: "Christchurch Robotics" <chchrobotics at lists.linuxnut.co.nz>
Sent: Tuesday, May 06, 2008 11:29 PM
Subject: [chbot] SMD experiment #1


> Hurro,
>
> An update on my quest for stampalikes; Last episode I'd decided to
> switch to SMD...
>
> Well, I picked up a couple of scrap boards from Huntsbury which had
> 0805, SO8 and SOT23 devices on them..
>
> I bought a cheap thermocouple thermometer off ebay, and waited..
>
> The thermometer turned up this morning, and as I was in town I went into
> Bricoes and picked up a 1400W toaster oven for the grand some total of
> $69.99 on special.
>
> I was originally going to get a 2nd hand one, then I found out how cheap
> they are new, and also someone pointed out that my workshop would
> probably smell like burnt cheese forever.
>
> I already have a pile of 0805 resistors, and I removed a SO8 IC and some
> SOT 23's from a dead Hard disk PCB.
>
>>From here on in the pictures are worth a thousand words:
>
> http://cpix.co.nz/myio/reflow
>
> look at them in order, 0 being first
>
> 0 - I used a syringe to put the solder paste on, (got that from Sicom).
>
> 1 - placed the components, badly as it happens, should have used better
> light and a magnifier, but this was
>
> 2 - stuck it in the oven, with the thermocouple right on top of the PCB.
> Note that I did this in the kitchen, hence low light...  I don't
> recommend this unless you have a very good relationship with your
> significant other!  Kate was out, and one of the kids is a bit sick so I
> didn't think it was a good idea to hide out in the shed in case he got
> up and couldn't find a parent.  (My excuse, sticking to it!)
>
> 3 - Raise the board up to 150c and hold it for about 2 minutes..  You
> can see the solder paste has started to flow a bit, this is not because
> it's melting, but because the flux is, which allows it to settle quite a
> bit.
>
> 4 - Reflow time, take the board up to 210c for 30 seconds, then cool in
> a semi-controlled way (Crack the door open a little).  The solder melts
> at ~185c or so.
>
> 5 - Ta-Da!
>
> I put too much paste on for the SOT23's by far, and misaligned the SO8
> IC, but the 0805's don't look too bad.  A bit of experimentation and I'm
> sure I can make them look quite tidy.
>
> Next step is an automatic controller, the onboard thermostat in the oven
> is junk, and using the thermometer and turning it on/off is only
> slightly better.  I've got some more bits coming to let me drive it from
> a PC, which will allow me to program in the 'profile' and log the
> temperature actual against target etc..
>
> I also need to look into flux solvents or no-clean solder paste, the
> loctite one I've used has fairly horrendous residue.  I used to use
> isopropyl on the through hold stuff, might try some on this.  Any one
> got a favourite for cleaning SMD stuff, or a source of syringe packed
> no-clean or water based solder paste?
>
> Onwards... :-).
>
> Cheers, Chris H.
>
>
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