We've had one flight program that soldered press-fit, but the design used over-sized plated holes that allowed the eyelet / saddle / spring core of the pin to slide into the hole.  We were told that their design required the I/O density of the press-fit connector, but (at the time) the lack of process control over the sizing of the holes for a proper interference fit between the pin and the hole wall ended up driving the decision to solder.  The pins were pre-tinned to strip the gold, and the holes were specifically sized to ensure solder flow through to the destination side.  To help with wetting the project used Sn62, the pins and holes were pre-fluxed with RMA, and lots of pre-heat was applied.  Reportedly a very tedious hand solder assembly process.  The hardware is still flying and working.

We've also had one flight program that installed the press-fit correctly - and without soldering.  The hardware is still flying and working.

I'm not sure over-soldering a properly installed press-fit is a good idea.  
1.  The termination is an interference fit that compresses the eyelet / saddle as the pin is inserted.  This compression loading is what develops a metal-metal bond between the pin and the wall.  Applying solder heat to the termination would slightly anneal the pin, reducing the compression loading. 
2.  A properly soldered termination requires all surfaces of the termination to be wetted.  The mechanical and electrical termination between the eyelet / saddle and the hole wall cannot be wetted if there is a gas tight metal-metal bond.  So, after the termination is annealed and the quality of the metal-metal bond is reduced, we have a non-compliant termination with a pretty solder fillet on the solder source side of the board, and likely no solder flow through to the destination side of the board.
3.  Preheat WILL be needed to get proper solder flow. Lots of preheat.
4.  The center-center spacing of the pins makes soldering "difficult".

None of the above prevents a customer from demanding that the press-fit be soldered.  It would be considered a Special Process.

Hopefully, qualification test will determine if the design meets the intended environmental / performance requirements.

Bob Cooke

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Tuesday, December 03, 2013 11:49 AM
To: [log in to unmask]
Subject: Re: [TN] Press Fit

Yes, for high rel, high vibration environment, you need to solder all the press fit connection.   You need to pre-tinned press fit socket prior to solder to remove the gold. If I am not mistaken, it is not the standard solder alloy you suppose to use for such application.

Sent from my BlackBerry 10 smartphone on the Rogers network.
  Original Message
From: Glidden, Kevin
Sent: Tuesday, December 3, 2013 11:01 AM
To: [log in to unmask]
Reply To: TechNet E-Mail Forum
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


______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________

This E-mail is confidential. It may also be legally privileged. If you are not the addressee you may not copy, forward, disclose or use any part of it. If you have received this message in error, please delete it and all copies from your system and notify the sender immediately by return E-mail.

Internet communications cannot be guaranteed to be timely, secure, error or virus-free. The sender does not accept liability for any errors or omissions.

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________
---------------------------------------------------------------------
This transmission (including any attachments) may contain confidential information, privileged material (including material protected by the solicitor-client or other applicable privileges), or constitute non-public information. Any use of this information by anyone other than the intended recipient is prohibited. If you have received this transmission in error, please immediately reply to the sender and delete this information from your system. Use, dissemination, distribution, or reproduction of this transmission by unintended recipients is not authorized and may be unlawful.

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________