Homebrew PCBs

Hi guys,

I'm having a play with solder paste and a homebrew reflow oven -- 
basically an Argos "Cookworks Mini Oven", 1640W quad-element (two top, 
two bottom), onto which I've grafted a Labfacility K-type thermocouple 
socket, a West Controls/CAL eCAL E6C PID controller, and a Crydom 
EZ480D18 solid-state relay.

Problem is, the squeegee I'm using isn't quite working...

What's happening is that the paste seems to go into the apertures in the 
stencil for the first inch or so, then all the paste starts making its 
way up the squeegee, towards the handle. The squeegee is a hard plastic 
handle, moulded onto a ~2mm thick piece of metal (stainless steel?).

Questions:
   1) Am I using the right tool?
   2) If not, what do I need? I've seen the squeegees Beta Layout 
(PCB-POOL) are selling for a couple of Euros, but I'm not keen on the 
idea of spending EUR5 on a squeegee, and EUR20 in postage.
   3) If I am using the right tool, what am I doing wrong? I left the 
paste out of the fridge overnight to warm up, so it shouldn't have been 
excessively cold...

Does anyone have any suggestions? I've seen the Sparkfun tutorials, and 
the PCB-POOL video, but haven't found any useful info on debugging the 
process...

-- 
Phil.
ygroups@...
http://www.philpem.me.uk/

i personally use a razor blade in a pair of vice grips.  not sure how big your board is but for the small boards i have done this comes out excellent (could see doing it w/ up to 4"x6" boards no problem).  i may have to clean the paste off the razor and put it back on the stencil, but that is about it.

bob

--- In Homebrew_PCBs@yahoogroups.com, Philip Pemberton <ygroups@...> wrote:

>
> Hi guys,
> 
> I'm having a play with solder paste and a homebrew reflow oven -- 
> basically an Argos "Cookworks Mini Oven", 1640W quad-element (two top, 
> two bottom), onto which I've grafted a Labfacility K-type thermocouple 
> socket, a West Controls/CAL eCAL E6C PID controller, and a Crydom 
> EZ480D18 solid-state relay.
> 
> Problem is, the squeegee I'm using isn't quite working...
> 
> What's happening is that the paste seems to go into the apertures in the 
> stencil for the first inch or so, then all the paste starts making its 
> way up the squeegee, towards the handle. The squeegee is a hard plastic 
> handle, moulded onto a ~2mm thick piece of metal (stainless steel?).
> 
> Questions:
>    1) Am I using the right tool?
>    2) If not, what do I need? I've seen the squeegees Beta Layout 
> (PCB-POOL) are selling for a couple of Euros, but I'm not keen on the 
> idea of spending EUR5 on a squeegee, and EUR20 in postage.
>    3) If I am using the right tool, what am I doing wrong? I left the 
> paste out of the fridge overnight to warm up, so it shouldn't have been 
> excessively cold...
> 
> Does anyone have any suggestions? I've seen the Sparkfun tutorials, and 
> the PCB-POOL video, but haven't found any useful info on debugging the 
> process...
> 
> -- 
> Phil.
> ygroups@...
> http://www.philpem.me.uk/
>

On 19/11/10 01:40, dubob4432 wrote:
> i personally use a razor blade in a pair of vice grips.  not sure how
> big your board is but for the small boards i have done this comes out
> excellent (could see doing it w/ up to 4"x6" boards no problem).

The board is a 16x10cm Eurocard.

Thanks,
-- 
Phil.
ygroups@...
http://www.philpem.me.uk/

what type of stencil?  kapton/mylar or steel?

--- In Homebrew_PCBs@yahoogroups.com, Philip Pemberton <ygroups@...> wrote:

>
> On 19/11/10 01:40, dubob4432 wrote:
> > i personally use a razor blade in a pair of vice grips.  not sure how
> > big your board is but for the small boards i have done this comes out
> > excellent (could see doing it w/ up to 4"x6" boards no problem).
> 
> The board is a 16x10cm Eurocard.
> 
> Thanks,
> -- 
> Phil.
> ygroups@...
> http://www.philpem.me.uk/
>

Couple of things to try...

Try different angles.  I use another PCB as the squeegee, and I have to 
lean it over more to keep the solder bead down near the stencil.

Mix your paste before using.  It needs to be creamy enough to "roll" as 
you pull the squeegee.  You might need to put more paste down to get 
this rolling action, then return the extra to the tub.

You can practice on an unetched pcb with no stencil; then it's easy 
enough to collect the paste and start again.  Once you get the rolling 
action down pat, try the real pcb.

On 19/11/10 02:02, dubob4432 wrote:
> what type of stencil?  kapton/mylar or steel?

0.1mm thick Polymex PET, from www.smtstencil.co.uk.

-- 
Phil.
ygroups@...
http://www.philpem.me.uk/

On 19/11/10 05:26, DJ Delorie wrote:
> Couple of things to try...
[...]

Fixed it!

I made a squeegee out of a sheet of K&S 2mm aluminium sheet (cut in 
half), a piece of 0.001" spring steel and some M4 machine screws.

And now for the Fool's Guide to doing this (if you're as crazy as I am):

   - Cut your piece of aluminium in half. You should now have two 
pieces, each around 5" square.
   - Cut a strip of spring steel to the same width as your aluminium sheets.
   - Measure the width of your spring steel. Mine was 1" wide.
   - Measure half that distance up from the bottom of the aluminium 
sheets, and draw a line.
   - Draw crosses on that line one inch from each edge of the alu sheet, 
and one cross in the middle.
   - Drill holes where the crosses are, using a 4mm bit. Do the same for 
both sheets. De-burr the holes and make them level with the rest of the 
metal (hint: a countersink works wonders for this!)
   - Stick a piece of masking tape over the edge of each sheet of alu.
   - Insert the screws and screw them onto the nuts, but leave them 
slightly loose (finger tight is more than enough).
   - Insert the spring steel strip into the gap between the two sheets 
of aluminium, on the side nearest the screws (where the masking tape 
is). Tighten the screws with a screwdriver and bull-nose (electrician's) 
pliers.

Now I need to figure out why I'm getting solder bridges in between my 
QFP pads... :(

-- 
Phil.
ygroups@...
http://www.philpem.me.uk/

sounds like a nice recipe :)

i too had issues w/ 1 or 2 bridges on just a tqfp-32 package and also a couple legs that didn't make contact, i think the solder paste i used needed more flux.  to fix it i laid a whole solder line over the pins and then used solder braid to clean it off - worked wonders w/ no bridges and all the legs made contact - perfect.

http://www.sparkfun.com/tutorials/101

hope this helps you out,
bob

--- In Homebrew_PCBs@yahoogroups.com, Philip Pemberton <ygroups@...> wrote:

>
> On 19/11/10 05:26, DJ Delorie wrote:
> > Couple of things to try...
> [...]
> 
> Fixed it!
> 
> I made a squeegee out of a sheet of K&S 2mm aluminium sheet (cut in 
> half), a piece of 0.001" spring steel and some M4 machine screws.
> 
> And now for the Fool's Guide to doing this (if you're as crazy as I am):
> 
>    - Cut your piece of aluminium in half. You should now have two 
> pieces, each around 5" square.
>    - Cut a strip of spring steel to the same width as your aluminium sheets.
>    - Measure the width of your spring steel. Mine was 1" wide.
>    - Measure half that distance up from the bottom of the aluminium 
> sheets, and draw a line.
>    - Draw crosses on that line one inch from each edge of the alu sheet, 
> and one cross in the middle.
>    - Drill holes where the crosses are, using a 4mm bit. Do the same for 
> both sheets. De-burr the holes and make them level with the rest of the 
> metal (hint: a countersink works wonders for this!)
>    - Stick a piece of masking tape over the edge of each sheet of alu.
>    - Insert the screws and screw them onto the nuts, but leave them 
> slightly loose (finger tight is more than enough).
>    - Insert the spring steel strip into the gap between the two sheets 
> of aluminium, on the side nearest the screws (where the masking tape 
> is). Tighten the screws with a screwdriver and bull-nose (electrician's) 
> pliers.
> 
> Now I need to figure out why I'm getting solder bridges in between my 
> QFP pads... :(
> 
> -- 
> Phil.
> ygroups@...
> http://www.philpem.me.uk/
>

On 19/11/2010 12:32, Philip Pemberton wrote:
>
>
> Questions:
> 1) Am I using the right tool?
> 2) If not, what do I need? I've seen the squeegees Beta Layout
> (PCB-POOL) are selling for a couple of Euros, but I'm not keen on the
> idea of spending EUR5 on a squeegee, and EUR20 in postage.
> 3) If I am using the right tool, what am I doing wrong? I left the
> paste out of the fridge overnight to warm up, so it shouldn't have been
> excessively cold...
>

I've done a bit of solder past printing. I used a commercially etched 
brass stencils.
I read about people often use steel squeegees. So I looked around for a 
good quality plaster scraper.
I bit like this 
http://image.made-in-china.com/2f0j00gBEtJRIcbKqZ/Stainless-Plaster-Scraper-8203B-S-.jpg

It should be thin flexible spring steel, and not bent or damaged in any 
way.
It worked great.


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