How to reattach an odd situation non-cpu heatsink? 3

[diogenes10]

I have a vc-31 mobo from an E-Machine T-4150. It had been moved from its original case and I am going to move it again.

There is a chip near the cpu which had a heatsink on it.
(The manual picture labels it as "Intel 845 MCH".)
The heatsink was held in place (loosely) with a piece of packing tape run over the heatsink and stuck on the mobo. When I remove the tape and the heatsink, I see,

On the mobo a green circuit board type of material with a small chip sticking up out of the center and a number of other little spots sticking up out of the green arrayed around the center chip.

On the bottom of the heat sink, there was black foam around the outside edge and a small square of pink in the center.
I didn't think to measure the heatsink when I was looking at it over the weekend, but as an example, if the heat sink was 2" square, there was a 1" wide band of black foam all round the outside edge and a small square - maybe 1/4" or 3/8" square- of pink stuff in the middle. The black foam did not feel sticky like it was originally an adhesive. I scraped on the pink stuff with my fingernail and it seemed more like tape than grease.

No evidence of a clip.

I don't know how this was fastened originally and don't know what the right way to put it back together is. The heat sink could not have been actually touching the center chip, so I don't know how critical reinstallation is.

Comments, advice, help???

Thanks.

 

[kmcferrin]

It's hard to say which was which, but one of the two substances was probably an adhesive strip of some sort, and the other was probably a heatsink compound or other thermally conductive material. Without knowing the exact layout of the circuitry inside the i845 it's hard to say where the hot spot on the chip would be (and consequently which substance was which).

On the bright side, there are a number of thermally conductive glues and even sticky pads that can be used to glue the heatsink back to the chip. Arctic Silver (everyone's favorite heatsink compound company) also makes a "thermal epoxy" which should do the trick. Just make sure to get "thermal epoxy" and not "thermal compound".

 

[johnbullas]

....Any wire loops or holes in the MB in proximity to the northbridge chip the heatsink was on top of? The original heatsink might have been clipped on?

http://techreport.com/reviews/2001q3/p4-sdram/845-northbridge.jpg

VC31:

http://www.fic.com.tw/product/motherboard/images/legacy/vc31_side.jpg

An IBM motherboard I just ebayed had a NB heatsink held on with such wires whereas my ABit MB has two plastic threaded knobs holding the heatsink and fan on

http://img.clubic.com/photo/00042692.jpg

Graphics card heatsinks are commonly 'glued' on where you don't see any clips or screws, cheap heatsink paste is commonly pink in colour ....

JB
Southampton UK










=========================
Transport Solutions
Southampton UK

 

[diogenes10]

jb

Your second link for the vc31 picture. The largeish aluminum heatsink in the center of the picture is what I am talking about.

That picture sure makes it look like there was originally a clip there. If there was, it's long gone on mine, but for starters I'll have another look at the board around the chip under the sink.

That (a clip) would make everything make sense because my guess is that the black foam around the edges of the heatsink is padding to protect all the little things other than the main chip in the center from touching the bottom of the heatsink. That would also explain how it came apart - all the foam pushing up overcame the tiny bit of sticking resistance that the cheap pink heatsink paste in the center had. The pink stuff is thicker than white heatsink paste I've seen, but it could just be dried out.

 

[paparazi]

According to the picture I have just been looking at, their are four loops coming through the motherboards PCB to attach the spring clip, the spring is like a torsion bar that goes over the heatsink and with a twisting motion then locates into two of the loops under tension.

This sort of attachment seems to be unique on Intel CPU based motherboards (I don't know why that is)

Martin


We like members to GIVE and not just TAKE.
Participate and help others.

 

[diogenes10]

Ok,

I think that gets me to what happened, but fixing options are looking more remote.

I found a completed auction picture on eBay of a T4155 which I figure ought to be close to my t4150 board. That appeared to have a clip like Martin is talking about hooked in a loop next to the agp port and the loop next to the cpu which is nearest the memory slots.

My mobo has both the loops on the cpu side of the 845 chip and it has the one on the agp side closest to the memory slots. The one right next to the agp slot is missing. There is a mounting location for it, but no loop. Somewhere along the line, either store demo or first machine owner, it must have come out and the clip got discarded.

Does that kind of clip turn over so it could use the hooks on the opposite diagonal where I still have two hooks? There is a bend in the clip in jb's side shot picture that would sort of imply that it doesn't. (the visible clip side in jb's side shot picture is going to my missing hoop location next to the agp port.)

And if it does, how would I possibly find a replacement?

 

[johnbullas]

the only answer I think is to use heatsink epoxy to glue the NB heatsink back on?

http://www.aria.co.uk/ProductInfoComm.asp?ID=2325

All depend on whether you want to ever replace it

....otherwise you are drilling the board to fit a new loop up and through the MB for a clip to engage (get a loop off of a scrap board, they are probably pushed through and held in place somehow rather than fastened down)

The black foam was probably double sided acrylic foam tape (possibly draught proofer) sadly lacking in the continuous pull necessary for effective "heat sinking"





=========================
Transport Solutions
Southampton UK

 

[kmcferrin]

Agreed, the heatsink epoxy is probably your best bet. Quick, easy, and relatively inexpensive. Since you can't actually swap out the northbridge chip, the permanence of the epoxy shouldn't be an issue.

 

[diogenes10]

In this motherboard, at least, the loops are soldered in. The location (HNB3) is there with two holes, just no loop.

I'm still wondering if there is some way to come up with a replacement loop and clip.

In the epoxy department, concerns:

1) I looked with a magnifying glass last night. There is some kind of varnish or sealer over the center chip and the adjacent areas of the green circuit board. If I put epoxy on there, it will attach to this varnish/sealer stuff. Will that varnish/sealer protecting the center chip stay on the green circuit board or will it come off under the weight of the heatsink?

2) Will it work? Approximate measurements-I couldn't get my ruler flat on the motherboard.
Heatsink 40mm x 40mm 1600 sq mm.
Foam band on back of heatsink 37mm x 37mm less a hole in the middle 17mm x 17 mm. = 1080 sq mm 67.5% of heatsink surface.
Chip in the center of the green Intel 845 (northbridge?) board. 7mm x 7mm = 49 sq mm. 3% of heatsink surface.

So an epoxy contact amounting to 3% of the total heatsink surface is expected to take the entire weight of the heatsink in a shear position, the epoxy is bonded to some kind of chip protective material that could peel off, and 67.5% of the heatsink is covered in material that is trying to expand (ie undo the epoxy connection), this for a heatsink the mfg spec'd with a clip to start with. It doesn't sound to me like a situation that can be successful.

3) How long would I have to stand with my finger in the proverbial dike for things to set up?

The contact area is 3% of the heatsink surface. There is foam covering 67.5% of the heatsink area that will be trying to expand and undo the connection. I would need to have good pressure on the epoxy area for whatever the setup time is.

 

[kmcferrin]

Maybe I'm misunderstanding you, but are you saying that there are multiple chips under the heatsink that it was previously making contact with? The green "board" that you're referring to looks like it's just the chip packaging. That shouldn't be an issue. At lot of times you'll get a situation like that when a chip was built on a particular die process and the mainboards were designed for that chip, then the chip is moved to a smaller die process for cost savings purposes, resulting in a smaller chip. They will sometimes mount that chip onto a package that looks like PCB to extend the connections to the original connection locations so that they don't have to re-design the motherboard for the smaller chip. Now that I understand that, I'm guessing that the black foam band was merely cushion to ensure that the heatsink was fit squarely.

At any rate....I just re-read your original post for clarification, and I see that the heatsink was previously being held on by a piece of tape. If that is the case then it probably was not making sufficient contact to provide much cooling at all to the i845 chip, so your chip may not need a large degree of cooling to begin with. If this board was designed with the original i845 chip in mind, then it may well have needed the extra cooling of a passive heatsink. But when a die shrink occurs (again, resulting in smaller chips) they also tend to require less electricity and and don't generate as much heat. So in your particular case the heatsink may not even be necessary.

Regarding whether the epoxy will support the heatsink, you won't know until you try it. But if you leave that foam pad intact then you'll at least have some cushion for a bit of extra stability. Or you could remove it entirely and just let the epoxy fight the shearing force of gravity. My experience with epoxies are that they make extremely strong bonds, and wouldn't likely be broken by an object that weighs only a few ounces. Have you ever seen the old "Kra-Z-Glue" commercials where they used a single drop to suspend a construction worker in the air by his hard hat?

Any setup time would be dictated by the manufacturer's recommendations, but epoxies usually set up pretty quickly.

 

[johnbullas]

http://www.techwarelabs.com/reviews/motherboard/epox/ep_4g4a+/

for some great photos!!!!! and....

"During tests, the heat-sink did get warm, but it was never too hot to touch. Moreover, there was an absence of thermal compound beneath the heat-sink, which reinforces claims that this Northbridge does not require an active cooling implementation."

Suggest you heatsink epoxy the northbridge heatsink on!!!!

The VC 31 PDF is here for a while:

http://www.ime.org.uk/pdfs/vc37_vg31_b1_eng.pdf

.......no mention of removing the northbridge heatsink

it is an Intel 845G northbridge and it looks like this

http://www.intel.com/design/chipsets/845g/pix/p4845g_381.jpg

I would guess the smaller 'chips' around the central core are covered by the heatsink if indeed present

=====
Supplier Contact Information for heatsinks:

Boyd Corporation

http://www.boydcorp.com

Chomerics, Inc.

http://www.chomerics.com

Foxconn Electronics, Inc.

http://www.foxconn.com

======

http://www.techwarelabs.com/reviews/motherboard/epox/ep_4g4a+/

for some great photos!!!!!

=====
Supplier Contact Information for 845 heatsinks:

Boyd Corporation

http://www.boydcorp.com

Chomerics, Inc.

http://www.chomerics.com

Foxconn Electronics, Inc.

http://www.foxconn.com

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Transportation Research Consultant
Winchester UK

 

[kmcferrin]

In those pics the smaller "chips" are actually just resistors. Very very tiny resistors. No worries about them overheating.