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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