THERMAL PADS: too sticky when *dis-assembling*. What to do?

[frogblender]

I have a PCB with a big piece of aluminum used for heatsinking.  The CNC'd aluminum touches all the hot components (DDR, power regulators, etc) using 1mm-thick  thermal pads.    There are 30 pads on the aluminum (ie. 30 components on my PCB need to be cooled).

Thermal pads come in 3 flavors:  not sticky, sticky one side, and sticky two sides.  I use sticky one side.

The problem is during disassembly:  despite one side not being sticky, with 30 pads shmushed in there, separating the aluminum from the PCB requires alot of force, with much wedging/peeling/fiddling, and most importantly, bending of the PCB, which breaks my BGA solder joints.

So the question:  Anyone have any bright ideas on how to disassemble the heatsink from a PCB that has lots of thermal pads?

[ataradov]

Use a thread or a fishing line and pass it between the board and the heat sink. It would let you cut the pads individually without applying to much force. This would destroy the pads, so if you need to do this often, it might not be the most economical solution.

[Coordonnée_chromatique]

I have a PCB with a big piece of aluminum used for heatsinking.  The CNC'd aluminum touches all the hot components (DDR, power regulators, etc) using 1mm-thick  thermal pads.    There are 30 pads on the aluminum (ie. 30 components on my PCB need to be cooled).

Thermal pads come in 3 flavors:  not sticky, sticky one side, and sticky two sides.  I use sticky one side.

The problem is during disassembly:  despite one side not being sticky, with 30 pads shmushed in there, separating the aluminum from the PCB requires alot of force, with much wedging/peeling/fiddling, and most importantly, bending of the PCB, which breaks my BGA solder joints.

So the question:  Anyone have any bright ideas on how to disassemble the heatsink from a PCB that has lots of thermal pads?

Redesign the board with larger dissipative arrays of vias around the hotpoints and use one thick thermal foam on the entire aera of the PCB.

[thm_w]

If the fishing line or floss idea doesn't work, does heating the assembly help? Could use a hair dryer.
Twisting the board instead of wedging might be more gentle as well.

[frogblender]

Thanks to all the dudes/dudettes who replied.

- fishing line would be viable... except the components are all different heights

- heating the whole thing up is worth a try.... if I do it, I'll report back here...

- redesign for more vias and whatnot (ie. heat transfers into the PCB) - this is what I want (on the next board):  inject heat into the PCB (many of the components in question have the big SMT "power pad" gnd on the bottom, and then remove the heat using the aluminum heatsink's standoffs (the aluminum heatsink is made from a single piece of aluminum, standoffs and all).


However... I've discovered I've foolishly used "tacky-2-sides" thermal pads.... when I should've used tacky-1-side 

[Coordonnée_chromatique]

- redesign for more vias and whatnot (ie. heat transfers into the PCB) - this is what I want (on the next board):  inject heat into the PCB (many of the components in question have the big SMT "power pad" gnd on the bottom, and then remove the heat using the aluminum heatsink's standoffs (the aluminum heatsink is made from a single piece of aluminum, standoffs and all).

You can also try to put some grease on the pads before mounting them.

[Benta]

You can also try to put some grease on the pads before mounting them.

+1

Normal white thermal grease in a thin layer would be my suggestion.