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Vicor DCDC modules on test PCB...need to mount heatsinks on them

Flyback

Well-Known Member
Hi,

We are doing a Test PCB containing one Vicor BCM4414xH0E5035yzz module, which will feed 4 paralleled Vicor DCM3623x50M53C2yzz modules. (these are all DCDC modules)
The BCM module will dissipate 84W. Each DCM module will dissipate 43W.
We are going to need heatsinks on them. We think the best way would be to put 3mm NPT holes near the 4 corners of each module….and then use these to fit an aluminium heatsink plate over each module’s surface….ie screws and nuts/washers, to pressurize an aluminium plate against each module surface. Would you say this is the cheapest way to do it for this test (only) PCB?

Also, the BCM module that we are using is the “board mount” version. (pg 39 and 40 of the datasheet). It appears that holes 10,11,12 & 13 are for screwing the module to the PCB…..then PTH pads 1,2,3 & 4 are for power input and output. But what are the screws for on pads 1,2,3 & 4?.......since the “board mount” version "solders" into the PCB…so why does it have these 4 screws at pad positions 1,2,3 & 4?

Also, the BCM module diagram on page 40 of the datasheet appears to be trying to inform us what are the dimensions of the PTH pads……..can you tell what the PTH pad dimensions are from that diagram?.......surely a round PTH pad should be described by its drill diameter and its outer diameter. Unfortunately I cannot ascertain that info from that diagram, can you?

DCM3623x50M53C2yzz Datasheet:
http://www.vicorpower.com/documents/datasheets/DCM3623x50M53C2yzz_ds.pdf

BCM4414xH0E5035yzz datasheet:
 

shortbus=

Well-Known Member
Most Helpful Member
Doing it again are you? Aren't you an engineer at the company you work for?

That said did you read the whole data sheet? Did you do what they said and go to http://www.vicorpower.com/powertools Quote the data sheet -
"Vicor provides a suite of online tools, including a simulator and
thermal estimator which greatly simplify the task of determining
whether or not a DCM thermal configuration is sufficient for a given
condition. These tools can be found at: http://www.vicorpower.com/powertools"

Or you could have Emailed Vicor, instead you come to the forum to get your information, as usual.
 

Flyback

Well-Known Member
Thanks, i appreciate they have their own heatsinks from Vicor, though we cant afford, and so wish to do a home brew.
The way i describe in top post may bend the pcb a little when the screws are done up, so i am thinking of a better way.......because we have 0805 size smd ceramics on, and these may get fractured by any board bending.

In fact, we are just thinking of winging it and simply resting a heatsink on top of each power module….(with no screws to pressure it down)…….but using some thermal paste to improve heat transfer.

sorry for the qu, i wasnt going to post, but then thought maybe home brew heatsink mounting methods are of interest to others....the way i gave in top post may be of some use to someone.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
In fact, we are just thinking of winging it and simply resting a heatsink on top of each power module….(with no screws to pressure it down)…….but using some thermal paste to improve heat transfer.
Thermal paste is only supposed to fill the imperfections in the surfaces, after the parts are clamped metal-to-metal anyway.
There should not be a measurable thickness of it after assembly.

You need some permanent pressure.

Or, use a heatsink bonding adhesive rather than thermal paste and just apply pressure until it is fully cured?

Make sure it's a proper one with high thermal conductivity though, there are a load of places selling silicone rubber based types recently which do not seem to have good characteristics, from what I've see so far.
 

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