We had a similar issue with a CM tinning Litz wire.  The dwell time on the solder pot was too long.

Thinking of the SAC305 alloy, have you tried the SN100C from Nihon Superior or SC995e from Metallic Resources?

Just a thought.

Phil

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Larry Dzaugis
Sent: Tuesday, July 08, 2014 7:00 PM
To: [log in to unmask]
Subject: Re: [TN] Dissolving pins

Another depends response.

Machine, flux, solder, PCB design, component and board finish all contribute.

Preheat can be applied before the machine with an oven, preheat in the machine, using the the solder to touch near the solder connection, running slow enough to pre heat the next joints, using an oversize nozzle, having the solder close, not touching the solder joint (not a very effiecient
method)

Soldering speeds can exceed 10mm/s under certain conditions.
Machine manufaturer may suggest 4 to 6 mm/s.

300C plus is not unusual on a robotic selective solder machine using SAC305.
A manual solder fountain at this temperature would eat up the PCB's as the timing is tough to control.

Selective soldering requires examination of the voiding in the joint, confirmation that the knee wall thickness is not destroyed by too long a dwell, basically qualify the product and process. Changing fluxes, solders, PCB finish process speeds, inerting and process temperatures can all cause dramatic changes in results.

An EMS refused to use the specified flux and SAC305 because it would cost too much. The result was a pile of scrap, missed delivery, dissatisfied customer (me) who had not been informed of the changes and an EMS looking at quadruple the capital cost if they used the less expensive material due to the increased cycle times if they implemented the less expensive materials. Changing from alcohol to water base fluxes takes much more preheat and energy to remove the water instead of alcohol. SAC305 melting point is 7 degrees lower than the substitute material. This process can bite back if care is not taken with change.

 Eroded pins, delamination, voids, insufficient hole fill, excess flux, solder balls, bridges and skips can result from short term thinking change.


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