I Always use sockets now Re: [sdiy] IC socket question

[Magnus Danielson]

From: harrybissell <harrybissell at prodigy.net>
Subject: Re: I Always use sockets now Re: [sdiy] IC socket question
Date: Thu, 12 Dec 2002 23:29:55 -0500

Hej Harry-Boy!

(Harry-Boy is the name of an advertisement cartoon used to promote horse track
racing here in Sweden)

> Hah... now I have to disagree with Magnus

Go ahead and disagree all you want! ;O)

I've never claimed to know all the facts on this, so additional information is
naturally welcome!

> (Hej Magnus ;^)

Hej, hej!

(Hej is Swedish for "Hi" in case you didn't get it, I used to tech Larry a few
words of Swedish during a private conversation.)

> The sockets that grip from the thin edge of the IC pin can be a
> problem. Yes... the contact area is smaller and there is more chance
> of the tiny contact point being gas tight...

Right. By gas tight we really think of being O2 tight, since the nitrogene
isn't there to worry us much, now is it?

> ... but the .1" spacing of the pins does not leave much room for a decent
> spring arrangement. These are usually a torsion (tuning fork style) spring
> that has a limited travel. Some ICs are fine, some fit badly. The insertion
> holes in the socket are usually small and alignment can be hard. They are
> usually loaded from the bottom of the socket and can trap flux.

Also, you run into the issue of plastic deformation as well as long term
fatigue.

> The "holds on the flat side" sockets usually have a ramp leading into the
> contact area formed by the outer leaf. There is some mechanical wiping
> action that scrapes the contact area clean...  The inner spring contact is rolled
> behind itself (its had to describe - have to cut them open)... which makes
> for excellent retention of a wide variation in pin thickness.

Yes, but these seems to age badly according to my experience. These depends on
the continous pressing force throughout its lifetime. They tend to get
relatively sloppery, especially when exposed to changing mechanical conditions.

There might be good and bad onces. In the end a number of close up photos
on a website together with good explanations would make an excelent helper for
people to understand the rational I think.

> And (as Magnus correctly pointed out) makes the insertion force VERY high
> on large pin count packages.  A 40 pin chip takes POUNDS of insertion force...
> better hold from behind or you break the board.

I agree! You really want to have the board flat on the bench when you do it.

> These sockets are really good for 8 - maybe 20 pin DIP. I never like the
> sockets for 6 pin dip no matter which kind... there's no retention at all...

Right.

> ZIF sockets anyone ???

Yes, but expensive.

In the end, sockets as such opens up a whole new can of worms and you need to
know a little bit of this and that in order to understand how to nail the most
of them early out.

Cheers,
Magnus