DPAK decal for Wave

[fizbim]

Has anyone every wave soldered a DPAK before ?

If yes, what does it's pcb decal look like ?
If no, why not ?

Thanks,
Fiz

[Tom]

I have never heard of wave soldering a DPAK because the thermal pad is too large for the wave to get under it. Wave Solder for SMT parts are limited to Gullwing, J-Lead (and this is sloppy) and Chip components.

Any SMT component that contains a flat lead cannot be wave soldered. These parts include the LCC's, QFN's, DPAK's, SON's, TO-252, TO-263, Flat Lead Amplifiers, some Resistor Networks, etc.

You have to get the solder underneath the component lead to insure a good solder joint. If anyone has any success at wave soldering SMT flat leads please let me know so I can revise my theory.

[fizbim]

I have to disagree with one of your points Tom. Flat lead packages can be wave soldered. SOD323 and SOT89 packages are good examples. It is not necessary to create a solder fillet underneath the component pin. A good toe fillet is sufficient. To accomplish this, as with other wave decals, a longer pad extension is used to "catch the wave" and attract solder to the pin and pad.

One potential problem with waving the DPAK is the size of the tab. If a full size pad is used on this tab, it may to heat sufficiently in the wave to solder. This is a problem with other components with large "wide" tabs as well. To deal with this, we narrow the pad so that it's much narrower that the solderable lead of the component - sometimes half the width. In addition, the pad is lengthend to catch the wave as described before. Since the component is glued for wave, movement or rotation of the component is not a consideration.

Personally, I believe that it can be done reliably. But I haven't found anyone yet who has actually done it. Maybe I'll be the first.

[Tom]

The typical assembly process for today's wave solder techniques is called selective wave. This is where all SMT components are assembled first (both sides) using infrared, reflow, and vapor phase (almost obsolete). Then the bottom side components are covered with a mask that has openings for the through hole pins. The SMT bottom side components are placed 5mm away from any through hole pin center. This is what we do for both prototype and production runs. The boards we do go into space, crash tests, set top boxes, computers, internet appliances and many other products. None of our assembly shops wave solder surface mount components any more. I do realize that some do, but that's their option.

You bring up some good points about wave soldering large DPAK leads and the heat that it would require could distroy the package. I personally never wave soldered a SOT-89 primarily because the industry (JEDEC & IPC) has been trying to obsolete that package for the past 10 years and we are not allowed to design it into any of our products.

[bbpcb]

"...SMT bottom side components are placed 5mm away from any through hole pin center...."
Is there the possibility to place smt components at a distance less then 5mm? Whic is the minimum space?

[Tom]

The distance requirements for placing bottom side surface mount components near through hole pins must ultimately be decided by whoever is doing the board assembly. They actually determine which parts are going to be selective wave soldered and which through hole components must be hand soldered.

At the same time the PCB designer has constraints that they must deal with and that has an impact on which through hole components eventually get hand soldered or selective wave soldered. Assembly and Design must work together as a team to achieve the ultimate results.

Do not assume that you know everything and that you can simply hand over a completed layout and dictate to assembly how they should do their job.

The minimum distance between SMT devices and through hole pins (on the bottom side) is currently set at 5mm at most large production assembly facilities. This rule can only be adjusted by your communication with your assembly shop.