Homebrew_PCBs

--- In Homebrew_PCBs@yahoogroups.com, Kaelin Colclasure <kaelin@...> wrote:
>
> I'm looking to stretch my luck by trying a design that uses all SMT packages. At the moment I am pondering how to tackle the thermal pads commonly found on SMT power converter packages (for an onboard buck converter).
>
> The data sheets commonly specify that a pattern of plated vias should be used to conduct heat from the thermal pad of the package on the top copper layer to the bottom layer. The idea, obviously, is to provide more copper surface area for radiating away waste heat. My problem with this is that I don't have a way to plate through holes. I am using old-fashioned copper rivets to connect between layers. And while the rivets are smashed pretty flat by the tool, you can definitely feel where they are, and the tool also tends to leave a slight deformation in the surrounding copper layer. I am concerned that this could cause problems with reflow soldering.
>
> I thought about simply making a larger copper area on the component side of the board, but the relevant data sheets are also adamant that circuit paths to supporting components must be as short as possible.
>
> I've got a couple of ideas to try:
>
> 1) Use riveted vias in a copper area that's as close as possible to the package without actually being embedded in the thermal pad landing. But will they still conduct away enough heat?
> 2) Forget the through-holes and stick some kind of heat sink on top of the package. But again, since the package is quite small, and not designed for a heat sink on top, will it work?
>
> Any other suggestions? Has anyone here tackled this sort of thing before?
>

--- In Homebrew_PCBs@yahoogroups.com, "Phil@..." <yahoo@...> wrote:
>
> I have no direct experience but I know what I would do. I would put the
> rivets in the thermal pad area first, cover the rest of the board with
> adhesive plastic film, and sand the rivets with maybe 320 grit wet until the
> heads were flush with the plastic, then bend the SMD leads slightly to
> compensate for the extra thickness.
> --
> Phil M.
>
> ----- Original Message -----
> From: "Kaelin Colclasure" <kaelin@...>
> To: <Homebrew_PCBs@yahoogroups.com>
> Sent: Wednesday, July 10, 2013 7:55 AM
> Subject: [Homebrew_PCBs] How to tackle thermal pads on SMT packages?
>
>
> > I'm looking to stretch my luck by trying a design that uses all SMT
> > packages. At the moment I am pondering how to tackle the thermal pads
> > commonly found on SMT power converter packages (for an onboard buck
> > converter).
> >
> > The data sheets commonly specify that a pattern of plated vias should be
> > used to conduct heat from the thermal pad of the package on the top copper
> > layer to the bottom layer. The idea, obviously, is to provide more copper
> > surface area for radiating away waste heat. My problem with this is that I
> > don't have a way to plate through holes. I am using old-fashioned copper
> > rivets to connect between layers. And while the rivets are smashed pretty
> > flat by the tool, you can definitely feel where they are, and the tool
> > also tends to leave a slight deformation in the surrounding copper layer.
> > I am concerned that this could cause problems with reflow soldering.
> >
> > I thought about simply making a larger copper area on the component side
> > of the board, but the relevant data sheets are also adamant that circuit
> > paths to supporting components must be as short as possible.
> >
> > I've got a couple of ideas to try:
> >
> > 1) Use riveted vias in a copper area that's as close as possible to the
> > package without actually being embedded in the thermal pad landing. But
> > will they still conduct away enough heat?
> > 2) Forget the through-holes and stick some kind of heat sink on top of the
> > package. But again, since the package is quite small, and not designed for
> > a heat sink on top, will it work?
> >
> > Any other suggestions? Has anyone here tackled this sort of thing before?
> >
> >
>

--- In Homebrew_PCBs@yahoogroups.com, "RDHeiliger" <rdheiliger@...> wrote:
>
> Have done a number of boost and buck converters, down to .5mm. Done them all single sided. If you fiddle with the layout you can get the traces pretty short. Look at the data sheets, there is usually layout recommendation art work. The most important point is to make the grounds to the chip and caps a single point ground, usually need to run a wide trace under the chip to do this, and the heat sink will be ground as well, this allows you to add extra copper for heat sink on each end. Also keep the inductor as close as possible with very large traces/pads. The recommended heat sink area is for the maximum current for the device, if you are running less that that you can get by with a little less heat sink.
>
> RD
>
> [Non-text portions of this message have been removed]
>

--- In Homebrew_PCBs@yahoogroups.com, "epa_iii" <palciatore@...> wrote:
>
> I know this is a Homebrew PCB group, but sometimes you have to get out of the box.
>
> I also am presently working on a power regulator design, using modern switching regulator ICs. It is all but impossible to find these ICs in a 0.1" pitch, through hole, DIP or SIP package. They all are in smaller, surface mount packages, at least all the ones I am willing to consider. I am currently exploring using the TI TPS54233 which comes in an 8 pin SOIC package that has 0.05" lead spacing so it is not too small for manual, at home assembly. But it also needs to have a bunch of thermal vias under it to use the foil on the reverse side to dissipate heat so I share your problem.
>
> For production quantities I will, of course, go to a professional PCB house and simply order the boards. They will probably only cost a few dollars each in 50s or 100s. But for prototype construction I can not afford $50 or $60 for each new PCB that I will need until the design if finalized. So I will need another way. One thing I have discovered is that I can order the TI evaluation board for this chip, for about $10 each. It will have all the proper thermal features (vias and foil on the back side) and it even comes populated with all the parts. I ordered two so I could experiment and even if a lot of smoke occurs, I can still buy more and pay less than just one custom PCB would cost. I will need to remove some parts and substitute others in my experiments, but that is a lot easier than making my own home brew boards. The kits with these evaluation boards came well packed and included a complete data sheet for the IC as well as instructions for the evaluation board.
>
> I have also ordered some SOIC to DIP adapter boards. I may have to experiment with these, perhaps using only short test periods and/or with a top side heat sync. Another possibility would be to drill and cut a hole under the IC area of the board and use a copper rod soldered to the bottom of the IC, through this hole. Fins could be added to that rod after it emerges from the back side of the board. This technique could easily be used with a home brew PCB. An aluminum rod heat sync with thermal compound may also work this way and be easier to implement than soldering.
>
> Paul A.
>
>
>
> --- In Homebrew_PCBs@yahoogroups.com, Kaelin Colclasure <kaelin@> wrote:
> >
> > I'm looking to stretch my luck by trying a design that uses all SMT packages. At the moment I am pondering how to tackle the thermal pads commonly found on SMT power converter packages (for an onboard buck converter).
> >
> > The data sheets commonly specify that a pattern of plated vias should be used to conduct heat from the thermal pad of the package on the top copper layer to the bottom layer. The idea, obviously, is to provide more copper surface area for radiating away waste heat. My problem with this is that I don't have a way to plate through holes. I am using old-fashioned copper rivets to connect between layers. And while the rivets are smashed pretty flat by the tool, you can definitely feel where they are, and the tool also tends to leave a slight deformation in the surrounding copper layer. I am concerned that this could cause problems with reflow soldering.
> >
> > I thought about simply making a larger copper area on the component side of the board, but the relevant data sheets are also adamant that circuit paths to supporting components must be as short as possible.
> >
> > I've got a couple of ideas to try:
> >
> > 1) Use riveted vias in a copper area that's as close as possible to the package without actually being embedded in the thermal pad landing. But will they still conduct away enough heat?
> > 2) Forget the through-holes and stick some kind of heat sink on top of the package. But again, since the package is quite small, and not designed for a heat sink on top, will it work?
> >
> > Any other suggestions? Has anyone here tackled this sort of thing before?
> >
>

--- In Homebrew_PCBs@yahoogroups.com, Kaelin Colclasure <kaelin@...> wrote:
>
> I'm looking to stretch my luck by trying a design that uses all SMT packages. At the moment I am pondering how to tackle the thermal pads commonly found on SMT power converter packages (for an onboard buck converter).
>
> The data sheets commonly specify that a pattern of plated vias should be used to conduct heat from the thermal pad of the package on the top copper layer to the bottom layer. The idea, obviously, is to provide more copper surface area for radiating away waste heat. My problem with this is that I don't have a way to plate through holes. I am using old-fashioned copper rivets to connect between layers. And while the rivets are smashed pretty flat by the tool, you can definitely feel where they are, and the tool also tends to leave a slight deformation in the surrounding copper layer. I am concerned that this could cause problems with reflow soldering.
>
> I thought about simply making a larger copper area on the component side of the board, but the relevant data sheets are also adamant that circuit paths to supporting components must be as short as possible.
>
> I've got a couple of ideas to try:
>
> 1) Use riveted vias in a copper area that's as close as possible to the package without actually being embedded in the thermal pad landing. But will they still conduct away enough heat?
> 2) Forget the through-holes and stick some kind of heat sink on top of the package. But again, since the package is quite small, and not designed for a heat sink on top, will it work?
>
> Any other suggestions? Has anyone here tackled this sort of thing before?
>