TO263 Twisting during soldering

[Henrik Kronborg]

Anybody who know a good solution to this problem?
I have tried different things. The best is when i split the back pad
in 4 smaller pads, but still with some trouble

[bbpcb]

Try something like the solution proposed by Philips for the SOT404(D2PAK)

[Henrik Kronborg]

Thanks, will see if that's the solution.

[John MacPhee]

I was experiencing the same problem and the solution was to balance the solder by replacing the single, large land under the body of the part with a row of pads identical to the lands for the pins (see graphic).

I should add that my solution is a workaround and a pain because you have to change to an alternate decal before processing the solder mask, and then change the decal again to process the paste mask. This can cause apertures to be duplicated and then that has to be resolved too. There may be a less complicated solution.

[Henrik Kronborg]

John,

How about thermal resistance?
I have a lot of heat I wish to get onto the toplayer and I'm not sure how well the body will be soldered when having solderpaste only on the top of the pad.

[John MacPhee]

Henrik,

I never had any solderability complaints with this decal which was used in high volume production.

A solder mask clearance area is included on the solder mask decal to allow heat transfer from the part to the board. To help with heat dissipation, put an as-big-as-possible plane area around the part and tie it to the signal which connects to the body of the part. If the same signal is present on an inner plane, add extra vias around the part to tie the inner and outer planes together to conduct heat to the larger, inner plane. That's standard practice here.

John

[André Klompe]

Can someone explain to me what is meant with "twisting" in the context of soldering.

I am currently designing a PCB that contains a 5 lead TO263 package and I might learn something of this.

So if anyone could explain this, please be so kind.

André Klompe

[John MacPhee]

I'll make a guess: if there's more solder under the body of the part than on the 5 lands, the solder under the body can draw the part away from the 5 lands and not necessarily in a straight line. Whatever method you chose to prevent that should be approved by your assembly house.

[Cadcrusher]

Is what happens when you have a large solder areas. What happens is there is so much solder the part will float in the solder.