Vitronics Soltec has a useful chart on time and temperature for Pb free
soldering.
It is available through their website.
http://www.vitronics-soltec.com/
It helps you find the edge of the process window.

Pre heat helps if there is only a dip.
For point to point the pre heat may be gone if the machine solder cycle is
in minutes.

Thermal reliefs around the ground pins matter.
My select solder time is much shorter on the PCB's that meet the company
design guide vs. the ones that don't.

Again it depends on what you are soldering.

I inherited hand soldering 9k pins to a 52 layer backplane.
It used SnBi  and the flux had to be matched to the lower solder
temperature.
The volume never went up high enough to jusitfy custom equipment.
The low temperature solder allowed replacment of the connectors.


On Mon, Jul 27, 2009 at 2:02 PM, Gabriela <[log in to unmask]> wrote:

> Of course I am!
> Where is it?
> Gaby
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /*
> Sent: Monday, July 27, 2009 8:24 PM
> To: [log in to unmask]
> Subject: Re: [TN] OOPS! The copper is gone!
>
>  Hi Gaby,
> You may be interested in my White Paper on how to specify PCBs for Pb-free
> soldering.
> Werner
>
>
>
>
>
>
>
> -----Original Message-----
> From: Gabriela <[log in to unmask]>
> To: [log in to unmask]
> Sent: Mon, Jul 27, 2009 1:56 pm
> Subject: Re: [TN] OOPS! The copper is gone!
>
>
>
>
>
>
>
>
>
>
> Right.
> Scrolled the internet for a couple of days, much on copper dissolution
> there.
> Another present from ROHS.
> Luckily we had no delamination because we used high Tg board material, but
> also luckily we have no BGA's on it, because my latest information is that
> High TG board material is bad for pad cratering. (another present from
> ROHS).
> I wonder how many cross sections I will have to do in order to validate the
> process.
> Gaby
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
> Sent: Monday, July 27, 2009 7:39 PM
> To: [log in to unmask]
> Subject: Re: [TN] OOPS! The copper is gone!
>
> Hi Gaby - you found the unhappy recipe for lead-free soldering: thick
> pwbs, lots of thru hole connectors and heavy internal copper layers =
> danger of copper dissolution. Both the IPC APEX and SMTAI International
> Conference proceedings for the last 2 years have some excellent papers on
> the topic of copper dissolution which may be helpful for your issue.  You
> may need to investigate using a different solder alloy instead of SAC305
> (?) to control the amount of copper dissolution. Good luck.
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
>
> Gabriela <[log in to unmask]>
> Sent by: TechNet <[log in to unmask]>
> 07/27/2009 11:56 AM
> Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
> Gabriela <[log in to unmask]>
>
>
> To
> [log in to unmask]
> cc
>
> Subject
> [TN] OOPS! The copper is gone!
>
>
>
>
>
>
> No surprise at all.
> Assembly went through lead free SAC selective soldering. Thick, 20
> internal
> layers motherboard. Immersion silver plated.
> Lots of connectors (not only), populated on both sides. Conventional 25um
> copper in holes, outer layers over 1/2 oz copper.
>
> Was soldered before with Sn/Pb.
>
> No free meals, haha.
>
> Want to redesign to ENIG - seems to be the only choice.
>
> I wonder if there is a thumb rule for selecting the possibility of
> selective
> soldering according to design and platings.
>
> Also, if ENIG is safe for this process, even if rework with SAC ot Sn100
> for
> hole fill and shorts must be performed.
>
> We will try to overcome the problem, in the meantime by using Nihon
> superior, but in order to get good hole fill for such a thick board, the
> parameters will be too harsh , I suppose.
> Cross sections look very beautiful- pads are gone, knee is gone, barrel is
> playing hide and seek, inner layers just end to nowhere.
> How did you wise people validate this process and never mentioned anything
> on the NET?
>
>
>
> Gaby
>
>
>
>
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