Heatsink for DPAK

You need to have a PCB pad for the 217 & 218....

Cheers

The DPAK is designed to be soldered to the surface of a PCB. If you want to use a metal heat sink, you should probably look for a TO-220 version that is made to be mounted on a heat sink.

John Popelish wrote in news:y8OdnULoU9S3XKHVnZ2dnUVZ snipped-for-privacy@comcast.com:

or maybe you could solder it to a copper HS and solder that to the PCB....if the leads will still reach. you could rout a hole in the pcb for the copper HS and glue it in flush with the PCB.

It turns out that there are some heat sinks designed for surface mount devices.

Dave.

Thank you very much. I'm gonna do a copper area large enough in order to fix the DPAK and the Heatsink for DPAK. Do you think is it ok ? I have a MOSFET DPAK where the drain should lies on the copper area. What do you think is the best way to solder it ? Remember that I should solder it by hand.

Thank you, Pasquale.

You may have a bit of trouble soldering this by hand. They are designed for reflow soldering. What equipment do you have available?

BTW, have you done the thermal calculations to figure out what size heatsink you actually need?

Dave.

Actually I don't have really good equipment (I have the stuff to solder by hand, "regular" equipment), for sure I don't have a reflow solder station. I know that is gonna be difficult but how can I manage to solder it by using "regular" equipment ? I need suggestions in order to get the best result with the equipment I have.

Not at all. I've seen some heatsink and I though to take the best one. I know that it's not good choice but I don't have any idea about the calculation. Could you help me ?

Thank you, Pasquale.

True, that's what they're designed for, but for a part with a pad more than a few mm by a few mm (for example the TO-252 has a pad 6.5 x 6 mm, quite big by most SMT standards) I find that a plated-through hole big enough for my soldering iron tip lets me do a very decent job of getting the part attached to the board. I'm sure there's some loss off cooling ability because there's no copper under part of the pad but I'm not pushing the limits.

Tim N3QE

I'm really interested in what you have done. Could you, please, send me some pics or something in order to understand better ? Or some links where I can check your procedure ?

Thank you, Pasquale.

No pictures handy, but: just put a plated-through hole underneath the thermal pad in a rectangle of copper. To solder the device to the plated through hole, turn the board over, stick the soldering iron through the hole to heat up the device and the board, when it gets hot enough to melt solder all around, stick in the solder and flood the hole. Solder will wick between the device and the copper pad.

I used this for a low-scale production AD9954 DDS a few years back.

Having the board pretinned helps a bit if you aren't used to it.

Having the hole of a good size for your soldering iron tip really helps. If not, you won't directly heat the devices thermal pad, just the board.

Tim.

I had a similiar question a while ago heres what I did. It's not ideal but it worked.The poor mans reflow method.

All I do is put a dab of solder on the draintab of the mosfet,and some solder on the drain portion of the footprint.Press the mosfet down and heat the drain tab at the same time.Keep going around heating the drain tab that extends above the case,and the drain part of the footprint.I used a small insulated screwdriver to keep pressure on the FET,while heating.

It took a few tries to get it down, but once you get the feel for it,it does the job in a resonable time.Just dont overdo the solder.

Good luck

Thank you very much. I'll try your method. What about the heat ? I'm trying to do some calculation if I need a heatsink or not. How did you manage that ? I've see that I should use the Rthjc, Rthja and so on but maybe a bigger copper pad will work. What do you think ?

Thank you, Pasquale.

First you need to know how much power your device is going to dissipate. This value will depend on how it's used in your circuit. If you don't know how to calculate this far then I suspect you may have more to worry about than whether or not you can solder a heatsink!

Dave.

I know, more or less, how much power my device will dissipate. For the MOSFET should be something like Pd = Rds_on*I^2. For this reason I'm trying to understand how to choose the right heatsink,

Thank you, Pasquale.

The device should have a degC/W figure for dissipation into ambient (no heatsink). If that temperature rise is acceptable in your application then no extra heatsink is needed. In practice because the device will be soldered to the board, it will have some extar heatsink already. If that temperature rise is not acceptable then you have to start looking at thermal resistance figures of the package and heatsink. Generally, you can get a ballpark figure by simply taking the heatsink degC/W figure and ignoring the thermal resistance losses (junction to case) in the package etc. The heatsink I quoteed is 25degC/W, not marvelous, but it helps.

Often with DPAK packages, a PCB heatsink is enough, and there are various ways to improve this with layout. But PCB heatsinks can be harder to calculate a figure for.

Dave.