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

[Magnus Danielson]

From: Cynthia Webster <cynthia.webster at gte.net>
Subject: I Always use sockets now Re: [sdiy] IC socket question
Date: Thu, 12 Dec 2002 16:54:23 -0800

Hi Cynthia,

> This is interesting to me because I'd been taught to insist on machined pin
> sockets over all others.  They call them "High Reliability" yet many folks
> here say otherwise!  (I know that they can be pure hell sometimes
> -just getting the chips into them without bending pins!)

There is a real issue with ICs and sockets. DIPs are made so that when they
are put onto the PCB, they will hopefully stay there until you've soldered.
This is done by letting the pins be slight bent outwards, thus allowing for
them to work as a kind of spring holding them put in their holes.

Naturally that makes the actual placement of holes being slightly denser than
where the lower ends of the pins actually hit. If you have a socket with
propper dimensions you will experience this as a problem. There are however two
solutions to this problem:

1) Slightly bend the pins by a small plier. Personally I use my favorite tool,
   a small Stirex to do the work. You better work pin-for-pin in order to get
   a good result. While this is a bit labour intensive (doesn't take that much
   time once you've got the hang of it) it will make the insertion process
   much more painless.

2) Use a professional inserter. There are specially designed inserters. They
   will grab the chip and bend all the pins flat down for you. You only need to
   aim and release to get it right. A good one surely cost money, but I am
   quite sure that this is the way to go for serious buissness folks. A good
   tool in the right hand both makes the job quicker and better and is worth
   it's money just cause you get less hassel and better quality.

Since what I do normally fall into DIY, I choose option 1, but you might want
to consider option 2. I'd at least recommend you to consider the option.

> Personally I always use military grade machined pin sockets on every chip
> everywhere now, (Gold if possible) because at the rate things are going with
> surface mount components and miniaturization... even lowly 741 DIP Opamps
> may sell for well over ten-dollars each sooner than you think!

Indeed. However, SMD is getting a hole lot easier to do. It's a matter of
training. Maybe it's time to make that "SMD DIY" site that a friend of mine
(who's well beyond DIY level into advanced prototyping) dreamed of doing
since he feels many people have an unecessary fear of SMD.

> For example I have some CA3094s that have turned out to be quite valuable
> and because I'd been using sockets, I was able to easily salvage them as
> practically good as new.

Good point.

> I'd be curious though to hear if anyone thinks the use of sockets like this
> actually ~causes~ more reliability problems than they fix?

IMHO will a good socket only lower the reliability (MTBF) slightly, but with
many other benefits. A bad socket is however a problem.

There is however an issue with all sockets you must recall, and that is how
they handle the tin on the IC components leg. All (but a few) DILs and SILs
have their pins covered with tin. This is to make them "wet" quickly in the
soldering process. The downside to this is that tin will oxidice which also
makes ICs sensitive to long storage times, they are intended to be used quite
quickly after manufacturing. When you solder on those legs, you burn through
what ever oxide is there with your solder's flux and embedd the pin in solder
and if you've done that process right and doesn't have made any other huge
errors (like mechanical stress, hazardous environment, thermically induced
mechanic stress etc) it will survive the lifetime. I've seen so many cases of
solderings that does not survive the lifetime of the box itself.

Anyway, most sockets only mechanically press onto the pin so that it touches
the tin. If you have a hazardous environment, or you only make a narrow
point-contact, or you experience much movements of the contact, you run into
the possibilty of that tin sheat to go oxidizing on you anyway. You could rub
of oxide by mechanical exercising.

You could imagine sockets grabbing the pin so hard that it cuts through the
tin layer for sure (it probably happends anyway to some degree for certain
holders), but the insertion force of those I don't want to think about.

The sockets I've seen (and now this is from memory) either spring to the flat
side (cheap once) or grab on the corner sides of the pins (expensive onces).
The later onces is able to cut through I think. The solder can glide away from
the corner, and there's 4 points of contact which is pair-wise pressing against
each other. I rarely use sockets, but prefer the later onces for obvious
reasons.

I haven't studdied the actual details of sockets as of lately, but at least you
got some of the knowledge that I've got on the issue. Possibly it makes it
easier to understand what the manufactures actually say and mean.

> I usually wait until a PCB board is totally wired to the pots and the
> switches and everything else ~before~ stuffing the chips into the sockets
> for the first time.
> 
> Does anyone think this is being too paranoid?

Well, no... I would do it like that without being paranoid, and so should you!

There's no reason to stuff them prior to that point anyway. When you've got
sockets stuffing them is what comes on about the last thing for a board.
So relax and just think it as "my habbit".

Cheers,
Magnus