PCB annular ring for a thermal relief. Is it necessary?

[steveo_steveorino]

Is it necessary to have annular ring on a thermal? I work in the CAM area of a high end circuit board plant and repeatedly receive CAD designs that contain plane layers with thermals w/o annular ring. In other words I would get a thermal (0450351045) Outer dim .045", Inner dim .035", spoke .010" and rotated 45. These thermals could have a .031" drill (.002" annular ring) or a .035" drill (no annular ring). Typically we would prefer .004" annular ring. Does it matter for heat dissipation or reliability?

 

[biff44]

If you are talking about a solder thermal relief, they used to be required with big leaded components. The big component, along with the copper plane, made it hard to solder the component without forming a "cold" solder joint.

Nowadays, when most parts are chip style, and operating frequencies are in the GHz region, thermal reliefs are NOT desired. A thermal relief would look like an unacceptable inductance for any sort of RF or high data rate digital applicaiton. I would do them only if there were some mondo big component leads to solder up.

 

[steveo_steveorino]

I actually did not explain well enough. These are component holes and the thermal are at these component hole locations on innerlayer planes. My question is, is it necessary to have the actual pad, or annular ring to make the thermal work correctly and if no pad exists or very little pad exists, does it cause reliability issues. There is several mils of copper in the hole wall that connects to the thermal spokes so there is connect.

 

[dindeds]

When heated Cu expands so thermal relief is required to prevent delamination on the pad area.
However yr question if annular ring reqd. on a thermal relief , I would say YES. I never design a thermal hole with 4 spokes connected directly to the component lead! 2mils is the min. requirement by the pcb maker.

 

[karesz]

Hi,
you NEED FOR A GOOD PCB DESIGN in all cases ANNULAR RINGs!!
You see; the wall of holes will be galvanized, the only possibility to have a connection (if it is to make) between that and a layers cooper is on the (not so very stabil) small cross section of (4) thermal spokes is very unsave/unreliable! It has a measure of 7-17-25 um thickness by 5-10-mil with, & practically no deepness into on the hole-wall galvanized "cooper- tube", you must have a contacting surface so big as possible = this maximum becoms you during a annular ring!

Im sure, that the 50um width of that is wrong too_to small, then you must it imagine; trough Multilayer passing intolerances are the layers usual with +/- 50 um passed over the others.
If your PCB producer can have a passing of +/- 50um, you MUST have annular rings width of (i.e.)100um for good/reliable contacting in all situations..

It gives you in worst case the 50 um (rest) annular ring width...

If the layers are positioned on worst case+/- 50um, you have practically no contacting into annular ring cooper(if it was only 50 um width, but depositioned with 50um...) from the hole wall...
K.