SMD solder paste


Neil Smith G4DBN
 

editing finger trouble...

f"ollowed by an IPA rinse, then a *clean* with hot deionised water with a drop of detergent, *then* apply paste..."

On 20/08/2020 13:09, Neil Smith G4DBN wrote:
followed by an IPA rinse, then paste and a clear with hot deionised water with a drop of detergent


Neil Smith G4DBN
 

I use Bismuth/Tin/Silver 138C paste for devices, and high-temp stuff to solder the PCBs to the spreaders.  Makes it lots easier if you ever have to swap out a device.  I have Chipquick 138C paste but I've also used Adafruit Makerpaste that works well and is way cheaper (£6 last time).

Flow and wetting with either type seems good on C101 and C111 copper grades with a < 5 micrometer RMS finish, although I have had a bit of balling where the finish is not that good (from using a sharp-corner slot drill to make the grooves in C101 copper, whcih leaves some half-moon work-hardened ridges which are almost imperceptible).

I've done a few devices just using Weller liquid flux and 0.5mm multicore wire which has been rolled into a flat ribbon.  That works in just about any finish.  These days I just polish the device slots with a fine Scotchbrite wheel with a drop of Brasso, then degrease with brake cleaner, then use a Brightboy abrasive rubber to burnish the faces, followed by an IPA rinse, then paste and a clear with hot deionised water with a drop of detergent, but I'm a bit peculiar in my habits.

Blowtorch and Ersin Multicore will probably work just fine.

Neil G4DBN

On 20/08/2020 12:53, G0FVI via groups.io wrote:
Hi all,
some advice needed! Been given a tube of SMD solder paste with a view to using it for copper spreader on LDMOS amps. This stuff is called 'Easy Print' and composition is 96.5% Sn, 3% Ag and 0.5% CuO (other stuff in there as well, made in Eastern Europe). I'm wondering if it's worth risking using this stuff (anyone else heard of it?). I know this topic has probably been covered before, but alternative recommendations would be appreciated (what are people using?), four LDMOS amp projects on the go here, rather not blow any more LDMOS devices (lost one recently to bias problems)!

many thanks

Andy G0FVI


Robin Szemeti - G1YFG
 

It is a common mix, I've not heard of the particular brand but I expect it will behave just like any other lead-free paste.

My advice would be to use standard 60/40 lead solder for the lower melting point and just place a zig-zag of solder under the device.  The lower melting point will pay dividends.

All I did for mine was to use some liquid solder flux on a cotton bud applied to the device and the slab, a zig-zag of solder in the trough  (See W6PQL's YouTube video) and then slowly heated the 1/2" thick copper slab on the gas ring ... as soon as the solder melted I waited a few seconds and then turned off the burner, gave the device a little shuffle left-right to make sure it was well bedded, and nudged it back onto the pencil marks. I would say it was in the molten state for about 30 seconds.  As soon as it was solidified, I lifted the slab off the ring and put it on the heatsink, easy peasy.

So my advice would be that solder paste sounds like a good idea, but I'd go with 60/40 tin lead.


On Thu, 20 Aug 2020 at 12:53, G0FVI via groups.io <Andrew.gilfillan=ntlworld.com@groups.io> wrote:
Hi all, 
some advice needed! Been given a tube of SMD solder paste with a view to using it for copper spreader on LDMOS amps. This stuff is called 'Easy Print' and composition is 96.5% Sn, 3% Ag and 0.5% CuO (other stuff in there as well, made in Eastern Europe). I'm wondering if it's worth risking using this stuff (anyone else heard of it?). I know this topic has probably been covered before, but alternative recommendations would be appreciated (what are people using?), four LDMOS amp projects on the go here, rather not blow any more LDMOS devices (lost one recently to bias problems)!

many thanks

Andy G0FVI


--
Robin Szemeti - G1YFG


G0FVI
 

Hi all, 
some advice needed! Been given a tube of SMD solder paste with a view to using it for copper spreader on LDMOS amps. This stuff is called 'Easy Print' and composition is 96.5% Sn, 3% Ag and 0.5% CuO (other stuff in there as well, made in Eastern Europe). I'm wondering if it's worth risking using this stuff (anyone else heard of it?). I know this topic has probably been covered before, but alternative recommendations would be appreciated (what are people using?), four LDMOS amp projects on the go here, rather not blow any more LDMOS devices (lost one recently to bias problems)!

many thanks

Andy G0FVI