Homebrew PCBs

Hello all,

OK, I take up electronics as a hobby. Hit roadblocks, find this yahoo 
group. Read like crazy and figure out how to make PCB's using the 
laser toner method. Great advice, get process down to 99% success 
rate.

Then I see a picture of a great PCB tinning job here - I think from 
Derek Hawkins. So I read, order some tinning paste (McMaster Carr 
#7774A11, page 3286 in online catalog), get a toaster oven, and 
voila, all should be set. But can't seem to do this one, and need 
advice from the experts in this group again.

I bring the oven up to ~440F degrees (according to Mcmaster, the 
melting range is 426-454.) and stabilize it (as best a toaster oven 
can). Bought a thermometer to put in the oven to check temp. Clean 
the PCB with acetone before coating to be sure no junk on it. Coat 
with ever so slightly water diluted paste, and put in the oven. 
Results:

1) I get a bunch of nice spherical silver solder balls sitting in a 
field of dried out grey mud (ie, the solder paste without the solder 
balls, dried out and coating the pcb)

I figure I don't have the heat high enough, but when I turn it up it 
just "burns" the paste.

Can anyone offer some suggestions as to why I get dried out paste 
with solder balls growing in it?
 
Thanks,
M

PS - I get the smae result if I dont dilute with water and just use 
right out of the jar.

On Sat, 03 Feb 2007 20:57:46 +0100, Mark Merclean <mamhouse@...>  
wrote:

>
> 1) I get a bunch of nice spherical silver solder balls sitting in a
> field of dried out grey mud (ie, the solder paste without the solder
> balls, dried out and coating the pcb)


If you wipe off the grey paste, is the underlying surface tinned?
I noticed i do not need to reflow the paste fully to tin the surface.
No idea why or how that works.

ST

I just use a small propane torch, just don't get to
close with the flame and you can see the solder change
when it melts.
mebo




--- Mark Merclean <mamhouse@...> wrote:

> Hello all,
> 
> OK, I take up electronics as a hobby. Hit
> roadblocks, find this yahoo 
> group. Read like crazy and figure out how to make
> PCB's using the 
> laser toner method. Great advice, get process down
> to 99% success 
> rate.
> 
> Then I see a picture of a great PCB tinning job here
> - I think from 
> Derek Hawkins. So I read, order some tinning paste
> (McMaster Carr 
> #7774A11, page 3286 in online catalog), get a
> toaster oven, and 
> voila, all should be set. But can't seem to do this
> one, and need 
> advice from the experts in this group again.
> 
> I bring the oven up to ~440F degrees (according to
> Mcmaster, the 
> melting range is 426-454.) and stabilize it (as best
> a toaster oven 
> can). Bought a thermometer to put in the oven to
> check temp. Clean 
> the PCB with acetone before coating to be sure no
> junk on it. Coat 
> with ever so slightly water diluted paste, and put
> in the oven. 
> Results:
> 
> 1) I get a bunch of nice spherical silver solder
> balls sitting in a 
> field of dried out grey mud (ie, the solder paste
> without the solder 
> balls, dried out and coating the pcb)
> 
> I figure I don't have the heat high enough, but when
> I turn it up it 
> just "burns" the paste.
> 
> Can anyone offer some suggestions as to why I get
> dried out paste 
> with solder balls growing in it?
>  
> Thanks,
> M
> 
> PS - I get the smae result if I dont dilute with
> water and just use 
> right out of the jar.
> 
> 



 
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>I get a bunch of nice spherical silver solder balls sitting in a
>field of dried out grey mud 

Copper mass is such that there is insufficient heat to raise 
copper/paste temperature to proper range in a reasonable timeframe. 
Instead, the flux dries out well ahead of solder melting and starts to 
do more harm than good. If this is a test using an unetched piece of 
board then it may never work in that oven.

You could try bringing the oven to maximum temperature for a while 
before placing the pasted board inside but even that may not work if 
there is too much copper. I use a hot air gun most of the time and an 
oven when there isn't too much copper to tin.

--- In Homebrew_PCBs@yahoogroups.com, "Mark Merclean" <mamhouse@...> 
wrote:
>

>I just use a small propane torch

This may be the best thing to use provided care is exercised. 
Furthermore, a torch is what plumbers use. Even though they state the 
melting point in the mid 400s, all indications are that higher 
temperature is needed before the solder flows freely. Wetting 
properties are definitely not on par with the more expensive stuff.

--- In Homebrew_PCBs@yahoogroups.com, pebo festus <mebo31@...> wrote:
>

Another alternative might be the tin plating method discussed at the 
bottom of this url page.

http://www.computronics.com.au/kinsten/

No heat required.

Regards,

Ross McKenzie
ValuSoft
Melbourne Australia