SMT solder mask

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SteveT

Senior Member
I'm fairly new to SMT. Only made less than 10 boards using the frying pan method.

I'm getting a little fed up with using a cocktail stick and a magnifier to apply solder paste to my surface mount boards and was wondering what other people do?

I could get a stencil made commercially, but, I very rarely make more than one of any board and as they cost about 20 odd quid per stencil, a little OTT for me.

I seem to recall hearing of people using something akin to a Craft Robo, which I believe is used for paper cutting ( a bit like a plotter with a knife blade) to make their own stencils. Do any of you use this method?

Has anyone made a CNC DIY version of the above? Is it cost effective? as a Craft Robo costs over 200 quid.

The biggest board I normally make is eurocard size 6"x4" (150mm x 100mm for the young 'uns) but thats for through hole stuff. I would expect SMT boards to be about half that in general.

Or is it just a case of 'grin and bear it'?

regards, Steve
 
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SAborn

Senior Member
I just solder the components using a fine tip on the soldering iron and no solder paste.

I have heard of others etching a solder mask from thin copper sheet, in much the same way to etching a PCB, but i have not done that as yet.
 
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MartinM57

Moderator
SMT - as in how big/what packages?

1206/0805 resistors caps? - solder directly
SOIC 0.05" pin spacing chips - solder directly

You can also solder TQFP/QFN directly - plenty of examples on the YouTube
 
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bgrabowski

Senior Member
I run an after school robotics club. We use SMT and we need to place and reflow a complete 'home made' PCB of around 60 components in a one hour session. The only way we can fit this in is for the students to use a solder mask to apply the solder paste.

I make the mask by printing the pcb layout onto overhead projector film. I drill the pads with a small drill-bit (size to be matched to the pad widths) in a pcb drill. This is taped to the PCB and the solder paste is spread into the holes using a car filler spreader or putty knife. A mask like this needs to be cleaned with white spirit between uses and will be good for at least 20 pcbs.
 
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RexLan

Senior Member
I would guess it is much easier to just apply the paste and then re-flow the board in a toaster oven. I have built many boards and can actually do two sided with SMT components and the toaster oven. It is very easy actually and I would be long done before you got a mask made I think.

I use a hypo needle that you can get at the pharmacy for $0.15 for insulin and with a big magnifying light/glass it is very easy and quick to apply to the pads. Get the biggest needle diameter they have or go to a Vet or feed store an buy a larger one.
 
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SteveT

Senior Member
Hi Guys, thanks for all the replies.

In an ideal world I would have perfect 20/20 vision, no shakes or problems with joints and a soldering iron with a tip the size of a gnat's teste :rolleyes: But I don't unfortunately. I'm a knackered 58 yr old arthritic diabetic well past his sell-by date and with none too perfect vision to boot so any ideas of me hand soldering anything as small as 0805 resistors/caps or SOIC would be totally out of the question. 1206? maybe, possibly, dunno, guess I'm gonna have to try that one. Seriously, I envy those of you who can do these things.

At the moment I like SAborn's etched mask idea. I use diptrace and after reading that I had a quick look and it's so easy to do with Diptrace. I'll be giving that one a go. Not too many places selling pre coated brass or copper at realistic prices so I guess a can of positive resist is called for.

Bgrabowski, whilst I like the idea - it could, for me, be a little labour intensive unless I was making more than one board.

RexLan, I've seen the syringes full of paste for sale but have always been put off by the price, never thought to fill my own. I just happen to have two brand new and unused in my 'This will come in handy some day' collection. Plastic tips on them though. I shall give it a go.
 
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SAborn

Senior Member
If you are real clever you can slik screen print on to copper sheet and etch it, although you must remember to use a plastic film/paint on the under side of the copper sheet.

And if you are really good you can simply do it with toner transfer onto the copper sheet and etch it. (remember to coat/paint the underside.)

In an ideal world I would have perfect 20/20 vision, no shakes or problems with joints and a soldering iron with a tip the size of a gnat's teste But I don't unfortunately. I'm a knackered 58 yr old arthritic diabetic well past his sell-by date and with none too perfect vision to boot so any ideas of me hand soldering anything as small as 0805 resistors/caps or SOIC would be totally out of the question.
Click to expand...
We are all approaching that problem, but one thing that changes a lot of that is being able to see what you are doing, seriously it 50% of the battle and i recommend you track a set of these.

002 (7).JPG

They are the cheap Chinese made ones and work better than a set i have of 10 times the price, here is Oz the El-Cheapo stores sell them for $5.00, and well worth the price for aging eyes, also able to be worn over glasses should you wear them as well.
Check ebay as its well worth the small investment and your soldering will improve greatly ( you have my guarantee on that ) :cool:
 
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Marcwolf

Senior Member
Alternatively if you can handle not having to look at the actual component there are a few USB microscopes/cameras available that can give a magnified view. The only difficulty is having to look at the screen whilst making the small movement with your hands. Also I have found some x5 and x5 reading glasses very cheaply from chemists or from EBay. I have a couple around my workshop. For extreme cases I have actually built in prescription lenses into a couple of my costumes so I don't have to wear glasses in them :)
 
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SteveT

Senior Member
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SteveT

Senior Member
Marcwolf

I'd seen those around and even had one with better resolution than the rest bookmarked with the intention to buy... but never got round to it. Now I think might be a good time/excuse to get one and give it a go.

Incidentally, the thing I use at the moment is just a pair of clip on x3 lenses that go on my normal reading glasses.
 
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SAborn

Senior Member
The cheap Chinese head set is well worth finding on ebay, you wont be sorry, i have seen / used many magnafiying systems over time and own several, but the $5.00 cheapies work the best and are light to wear, i even have a adapted set in my welding shop as a grinding mask so i can see the finer details if needed.
 
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SteveT

Senior Member
Looks like I have 2 basic choices from ebay the first http://www.ebay.co.uk/itm/120887475013?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2648 is a 4x magnification but with an extra 4x lense that can be flipped down pluss the rotating circular lense is 5x.

or http://www.ebay.co.uk/itm/151047634339?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2648
which comes with a box of lenses but even using 2 lenses only can go up to 6x (which is better than I use now).

I like the look of the first one because you can remove the lamp (and batteries) to save weight.
 
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