How to solder HTSSOP heatsink without reflowing the board?

[vinicius.jlantunes 50]

I am working on a breakout / test board for a TLC5940 that I got in one of those HTSSOP-28 packages, with the little metal back that you're supposed to attach to a copper area using thermal vias and use as heat sink.

 

My question is: is there a way for me to "hand solder"  that part without reflowing the board? Will it work if I try to heat it from the back of the board with a soldering iron, or is the copper area too large and it will never heat up to a point where the solder melts? Would some flux maybe help?

Should I just wack some thermal paste between board and component and not even bother trying to solder it? I do not plan on using high currents, but thought it would be nice to have it properly done.

 

I will get the boards made by Elecrow, and will use HASL finishing as I guess that would make it easier to solder that part, am I right?

 

I am using the new Altium Circuit Maker, therefore you can check the project here (still work in progress): https://workspace.circuitmaker.com/Projects/148E0C7D-1CA4-472C-8BE4-44C2DBD13361

(I guess, never shared a project, hope the link will take you there).

 

If you have any tips on the board itself also feel free to comment. My first board using Circuit Maker and well, haven't done many elsewhere, so I'm open to suggestions!

 

[spirilis 1,265]

I had one of these and I *think* I satisfactorily soldered it...

The key is to have vias in the thermal pad on the PCB so you can shove your iron on those and help the solder melt.  Solder paste on the thermal pad is a must, and it probably makes sense to spend some time "warming up" the ground plane just outside the chip to make it easier to melt the solder.  Probably a very tiny amount of no-clean flux paste on the chip's pad would help too (I didn't have that at the time).

 

Perhaps a heat gun under the board would help to "warm up" the ground plane in preparation for the critical soldering-iron-hit that finally melts the solder paste.

Otherwise, I bet some thermal paste would do the trick well enough assuming the thermal pad isn't also relied upon heavily for the chip's GND reference, which it might be.

[oPossum 1,083]

It is possible to do thermal pads without a reflow oven or hot air.

 

[vinicius.jlantunes 50]

Thanks @@oPossum! I will have a look at the video later at home.

[spirilis 1,265]

Yeah the large window of solder-unmask around the bottom is also important (which I included in my board).  I think one of my problems was I didn't have a large soldering tip like that guy.  I may have one in my drawers, just need to find it & switch it out the next time I do this.

[RobG 1,892]

I have been using this technique for chips like W5200, W5500, TLC5947, TLC5951, etc., and...

Make sure you have exposed area under the IC and on the opposite side (tStop and bStop layers)

Use few 0.023 or 0.027 vias. Those sizes work well with 0.020 solder, I just stick it in the via and touch with iron

If you use footprints w/o heat pad, make sure you don't have any tracks under the IC.

 

[vinicius.jlantunes 50]

I will have a look at my design and incorporate your tips @@RobG. I am still learning this Circuit Maker thing so let's see how it goes!

[Lgbeno 189]

Many different tricks to do this, the ones mentioned above are good.

Additionally I recommend using solder paste. Its glorious combination of solder and flux ensures that you get good solder coverage. Handy in whatever solder scenario.

 

You can do a toaster reflow too, dab on some paste then 2 min at 250 deg f, 3 min at 450 deg F. I use two different toaster ovens that I bought for $5 each at the thrift shop. Works surprisingly well.

 

 

Sent from my iPhone using Tapatalk

[zeke 693]

I have resurrected over 75 boards at work by carefully using a 1200 Watt hot air paint stripper to remove and re-install 288 ball BGA packages. 

 

The key is to heat and cool the board evenly over a controlled amount of time.

 

Burnt FR4 is a nasty smell.