Hi, David,
I have no data, personally, on field failures for press-fit connnectors -
only know that we (when I was with one of the largest avionics OEM's) used
them on Backplanes for many years without major problem. Mostly the
equipment was housed in compartments being fed with conditioned air at 25
deg C, so there were no real huge temperature swings in practice in many
applications.
Press fits were/are used primarily to permit wire wrapping of backplanes.
This would allow quick and cheap customisation of the boards, and have been
an accepted hardware standard for decades. Basic Backplane design and
materials don't seem to have changed significantly in that time, unlike
'ordinary' boards, so maybe that's the difference - don't fix what ain't
broke, but watch out for boards using modern materials.
Just a 2cent thought.
Peter
David Douthit <[log in to unmask]> 28/10/2002 02:05 PM
To: "TechNet E-Mail Forum." <[log in to unmask]>, DUNCAN Peter/Asst Prin Engr/ST
Aero/ST Group@ST Domain
cc:
Subject: Re: [TN] Press fit connectors...
Peter,
Temperature variations is one of the field failure modes that causes
problems.
Avionics equipment can experience 100 degree C ambient temperature swings
in 15 or 20 minutes.
This will cause contact failures in press fit connectors (particularly
nickel finishes!).
You must consider the end use environment before using press fit!
Without understanding of these requirements you are simply "throwing it
over the wall"!
David A. Douthit
Manager
LoCan LLC
[log in to unmask] wrote:
> Steve,
>
> It's exactly VME Backplanes that we use press-fits for. They're about the
> same number of layers, but much thicker for rigidity (0.250" !) We have a
> bunch of small discretes on the underside and some SOIC16's etc. Really
> don't envy you the BGA RAM chips with that thickness of board and
press-fit
> conns. Oh! The Flexure! I hope your board's physical support is really
good
> so you don't pop the BGA's off during pressing (I presume you're fitting
> components first, as I don't know what thermal profile temperatures will
do
> to the connector pin: hole barrel interfacing.Certainly the pins will
> expand and the hole diameters will contract with temperature and the pin
> corners will cut even more into the plating. Then when they cool again
> ....)
>
> Good luck, Buddy!
>
> Peter
>
> [log in to unmask] 28/10/2002 09:01 AM
>
> To: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group@ST
Domain, [log in to unmask]
> cc:
> Subject: Re: [TN] Press fit connectors...
>
> Thanks Peter!
>
> I'm about to build a VME card that's density is beyond belief, that
> utilizes press-fit connectors. When Jack suggested that they be soldered
as
> a standard practice, I almost had a coronary!!!
>
> Just to let you know, we're talking about a 16-layer, .062" thick board,
> with a of bunch .020"-pitch components on the bottom, along with BGA RAM
on
> the bottom...
>
> No wave at all...so Jack, do we hand solder this stuff? Remember, we're
> talking 16-layers...
>
> -Steve Gregory-
>
> Hi, Steve,
>
> Press fit connectors are just that - press fit - and they are designed
not
> to be soldered. The quality, diameter and tolerance of the plated hole
> into
> which they are pressed is critical, though, for successful press
fitting,
> but you must know all this. If you then solder the pins you'll have the
> devil's own job getting them out again, quite apart from not having
enough
> clearance in most cases
>
> At least for class 3 boards, wherever I've been, we mechanically support
> them as well - nuts and bolts, though I've also seen them just pressed
> with
> no mechanical support, and they've worked fine, especially high
pin-count
> conns with plenty of insertion/extraction force. Check out the Harwin
.com
> site for info.
>
> If incompetence is being sought, I suggest that your customer review
their
> requirements, assumptions, source information, etc., before slinging mud
> at
> you.
>
> Peter
>
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