Good 68 pin lcc socket with hole for mounting

[jmk365]

Where can i find a 68 pin lcc socket with a hole for mounting a sample. I need to be able to place the sample on a coldplate in a dewar which so that it is in contact with the plate and still contacts the pins on the socket.

The attached file shows a rough ProE model of the coldplate. As you can see the raised section is where the sample will be placed, so where can I find a 68 pin lcc socket that has such a hole in the center. All the ones I have found have no square holes in the center.

Thanks

 

[mgb_phys]

You just cut the hole in the centre out of any plastic PLCC socket.
I haven't seen any that come with a cut out.

 

[jmk365]

thanks, i figured i would probably have to do that but I just wanted to double check

 

[berkeman]

One option would be to use a socket that has an open top, and after the chip is in the socket, invert the socket onto your coldplate. A socket like this:

http://www.locknest.com/newsite/products/lcc/index.htm

If you're trying to hit the thermal pad on the underside of some chips, then this method would not work. But if you're just trying to get wide thermal contact with the plastic of the IC on either side, then you can hit the top with the right socket.

 

[mgb_phys]

Usually for CCDs / imaging arrays in PLCC sockets, just cut a hole for the cold finger.
Another tip, bend the pins on the plcc inward slightly with a small screwdriver (or a pin) before inserting the chip - it helps to ensure that they keep good contact while the device cools, it's sometimes a bit unpredictable how the plastic behaves at very low temps.
And be careful to make the hole sized so that the coldfinger can't touch any of the pins/tracks if the socket moves sideways while it is cooling/contracting.

 

[f95toli]

This is -believe it or not- actually a well known problem and there doesn't seem to be a good solution. I occasionally use ceramic chip carriers that fit in LCC sockets (the sample is wire bonded to the chip carriers) and have used them at temperatures from 270mK to 100K (below 270mK there is no point, you can't use more than a few wires anyway).

The socket you linked to should work. However, you might runt into problems if you start making holes in LCC sockets since the chips do not fit quite as well anymore (since the socket is less "stiff") meaning you might loose contact when the samples is cooled down.
A few years ago I worked on a 300 mK system where we tried various solutions (including drilling holes); eventually we gave up and simply made our own socket which was made using a "frame" of tufnol and the contacts were beryllium-copper pogo pins that pressed against the back of the chip carrier; it was a pain to solder but once made it was very reliable.

What temperature are you working at?

Also, I don't know if your samples are sensitive to magnetic field, but if they are you need to be careful; the metal parts in most sockets are have a nickel layer underneath the gold (sticking layer) meaning they are actually slightly ferromagnetic. This is not a problem for most people but can cause real problems is you are measuring sensitive devices (e.g. SQUIDs) .

 

[jmk365]

Thanks for the advice. The temperature is around 70K and there will be no magnetic field. I was thinking of using one of the following sockets? Do you think they would work well or do you know of another that is better?

http://www.kvconnection.com/ProductDetails.asp?ProductCode=06-110-F4
http://www.cippsites.com/Merchant4/merchant.mvc?Session_ID=8f4d57cfd3a75435c1c59692acdec94d&Screen=PROD&Product_Code=68PLCCSKT&Store_Code=melabs - A little pricey, but it has a hole and looks sturdy
http://www.allelectronics.com/make-a-store/item/PLCC-68W/68-PIN-PLCC-SOCKET-THROUGH-HOLE-STYLE/-/1.html
http://www.allelectronics.com/make-a-store/item/PLCC-68/68-PIN-PLCC-SOCKET-SURFACE-MOUNT/-/1.html

 

[mgb_phys]

We just used a simple gold plated one from our regular parts catalogue (farnell) at 77K.
ps. One of the ones you list is surface mount - it's tricky to solder surface mount with multiple rows of holes underneath without a reflow oven.