TPA3255EVM: Heat sink faulty (yes, srsly)

Hi Gord.

Can you take a picture of the fault heat sink?

BR.

Wei Qiu.

https://www.dropbox.com/s/jsre593ilav3ibv/EVM1.jpg?dl=0

https://www.dropbox.com/s/rrlj5t7lrjsh4kb/EVM2.jpg?dl=0

https://www.dropbox.com/s/u8alarwbzd0an69/EVM3.jpg?dl=0

You can see the heat sink compound has not even spread out from where tit was applied, only the peak of the dollop made contact.

Hi Gord

    We are sorry about this, seems the manufacturing side didn't doing well, the heat conducting glue didn't spread evenly causing this problem. The heatsink it self shouldn't be a problem, you can see from below picture, the heat pad on the heatsink is only 1mm distance between the bottom of the leg. And our device height should between 1mm to 1.2mm. Maybe you can re-smear the heat conducting glue on the top of our device, should solve this problem.

I've been using heat sink compound (it's *not* a 'glue') for about 40 years and never have I heard of using it to fill 160 cubic millimeters of space (in all 3 planes).  It is meant for filling tiny voids.  This is not a good solution. 

Plus how many other ones are like this and is it going to make other EVMs prematurely fail (and hurt the product/manufacturer reputation)?

Hi Gord

Gord Parker said:

using it to fill 160 cubic millimeters of space

    May I know how do we calculate this value? 

   Actually I'm trying to say, when the heatsink is mounted on the PCB like below picture, the blue line is the PCB, where the foot of the heatsink stand. So the red area is for our device, the height of this area is only 1mm. But our device is 1mm to 1.2mm high, so the heatsink should always press close to our device. 

160 mm^3 = 10mm x 16mm X 1mm gap (the gap between the chip top and the heatsink I mentioned earlier.)

With everything soldered down correctly, (assumedly as I didn't unsolder anything), the chip is 10mm x 16 mm and there is still a 1mm gap between the chip and heatsink.  

The heat sink compound didn't spread out because there is such a large gap.  And heat sink compound is not designed to fill a gap like that, it is for very small gaps.

As you said: >>so the heatsink should always press close to our device<< and having used several of these EVMs, this one is very different and does not press close to the device. 

Please correct me if I am wrong, but I don't think 1mm is "close to our device" in the scale of PCBs and packages of this scale.

And the heatsink I had to machine fits properly like all the others I've tried it on, so I think the factory heatsink is bad.  I sent you a picture and you can see the area that is supposed to contact is less pronounced (less tall?)

Hi Gord

   Our device height is 1mm to 1.2mm, and heatsink height should be 1mm, so usually there should be no space between our device and heatsink. But according to your description, seems this heatsink has some problem, maybe higher than the spec. Sorry about that. We haven't receive other report about this failure, will continue check on this.