Hello Steve
Thanx Steve. That's deep trawling, but obviously not the thread of experts I
was mentioning!
Perhaps I have conflated two threads in my memory but I was thinking of more
like 5-6 years past. So far as I recall the thread didn't start as Pressfit
but morphed to it - I think. The problem is that TechNet forum reflects real
life so there are topic cycles as each generation of engineers rediscovers
stuff the previous generation forget to tell them about or they ignored.
After a number of repeat cycles they tend to blur somewhat!
Regards
Mike
-----Original Message-----
From: Steve Gregory [mailto:[log in to unmask]]
Sent: Tuesday, December 03, 2013 6:19 PM
To: [log in to unmask]; [log in to unmask]
Subject: RE: [TN] Press Fit
Hey Mike!
Let's turn our way back machine to September, 1999:
>Subject: Re: Okay, try not to laugh...
>
>From: Michael Fenner <[log in to unmask]>
>Reply-To: Michael Fenner <[log in to unmask]>
>Date: Wed, 22 Sep 1999 20:34:55 +0100
>Content-Type: text/plain
>
>If correctly done Pressfit makes a cold metallurgical bond rendering a
hot one made by
>soldering unnecessary. If you solder a Pressfit you lose any advantage
from the Pressfit
>joint as the thermal excursion is beyond its design limits and has
probably bust it, let
>alone the pth barrel etc., and end up with a solder joint which at best
looks OK. Or maybe
>that's worst as it looks OK.
>
>----- Original Message -----
>From: Stephen R. Gregory <[log in to unmask]>
>To: <[log in to unmask]>
>Sent: 21 September 1999 22:39
>Subject: [TN] Okay, try not to laugh...
>
> Hi Techies!
>
> This one you'll get a kick out of. I've been working quite a bit in
wave
> solder here recently, and today an assembly that has been built once
here
> before (prior to me starting here) came down to my area to be waved
soldered.
>
> It had suprised me to see the boards at wave solder because earlier I
had
> noticed that there was two right angle connectors being pressed into
the
> board. I asked why were they bringing me the boards and I was told;
"To wave
> the connectors..." (they were the only through-hole on the board BTW)
"But
> why?" I asked, "They're press-fit connectors!" The reply was; "Well,
that's
> the way we did them last time..." I tried not to laugh...honestly I
> did...kept a pretty straight face actually.
>
> So when ya'll get through laughing, tell me this, what kind of
problems can
> occur from trying to wave solder press-fit connectors...besides the
obvious
> barrel fill issues that come from the design of compliant-pin press
fit
> connectors keeping the solder from flowing up the barrel..."No wonder
we had
> so many solder problems last time.." I was told by a few of rework
> operators here...kept a straight face on that comment too. (These are
Harting
> press-fits by the way, a kind of triangular spade looking pin that
almost
> fills the whole barrel).
>
> Me in my logic, thinks that since the connectors were pressed in,
there's got
> to be some slight barrel deformation and/or strain put on the barrel
walls.
> Then running it across a 500-degree pot of molten solder just adds to
the
> strain from the thermal expansion it's going to see and could create
some
> problems.
>
> Now I might entertain wave soldering a press-fit if I got a board in
that had
> holes way out of spec and the connectors could be almost pushed in
with your
> hands. But these connectors have good contact throughout the barrel,
and the
> pins have been deformed (complied) with the barrel as they were
pressed-in.
>
> There's a rumor a-foot that some think we should wave them anyway so
they
> look like the ones we built before. I think that's almost the
stupidest
> reason I've ever heard to do something like that. I wanna know if
there's
> anything detrimental to waving these boards with a nice tight
press-fit
> already done...I think there is. What do ya'll think?
>
> -Steve "I'm about to pull my hair out!" Gregory-
>
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: Tuesday, December 3, 2013 10:08 AM
To: [log in to unmask]
Subject: Re: [TN] Press Fit
We have had a go round on this exact topic before when learned types
went into the matter in some detail with references. The conclusion was
pretty well as Kevin summarises: solder or pressfit but not both.
Searching the archive will no doubt turn it up.
Regards
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Glidden, Kevin
Sent: Tuesday, December 03, 2013 4:01 PM
To: [log in to unmask]
Subject: Re: [TN] Press Fit
Bad idea.
For one thing, most all press-fit contacts have a hard gold finish. If
you solder this, your solder joint will be a ripe candidate for gold
embrittlement. It is a J-STD-001 requirement to remove gold prior to
soldering. And tinning prior to insertion would increase lead diameter
and insertion forces, likely leading to PTH damage.
Second, press-fit insertion is an interference fit. There was a
discussion just yesterday in TN about the criticality of getting the PCB
hole spec just right for both the drill and finish sizes. The
installation results in a hoop stress to the PTH. One can only imagine
what can happen if you then take that to solder temperatures. Lead
interference with the PTH for TH soldered applications is a no-no.
My 2 cents.
Kevin Glidden
-----Original Message-----
From: Vargas, Stephen M [mailto:[log in to unmask]]
Sent: Tuesday, December 03, 2013 10:36 AM
To: [log in to unmask]
Subject: [TN] Press Fit
All:
I have a customer who is specifying a press fit connector to be
soldered after the press fit operation. I've never heard of this and I
was wondering if there is any quality/reliability data in the industry
as to why one should/shouldn't do this. Our customer's explanation was
that it would add mechanical integrity to the joints. Thanks in advance.
Regards,
Steve Vargas
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