Hi -bogert4,
Werner is right. You haven't given us the preheat temp info, however the
flux's preheat range should be listed on the datasheet from Kester and it
applies to both top and bottom measurements usually.
Things like whether or not the backplane has ten 2 ounce copper ground
planes in it all come into play and only measurement of actual (topside)
board surface can determine if the preheat is proper or not. I should add
that wavesoldering a .125 thick backplane requires a lot of preheat, dry
pwbs, lots of masking, and minimization of the preheat gradients with
respect to top-bottom and leading edge - trailing edge on the board. The
maximum preheat is not what would worry me, as I doubt you are able to
maintain the minimum topside preheat temperature required with only one
preheater.
I once built .125 thick wavesoldered circuit cards for a former employer
and had to bake moisture out all of the boards before wavesoldering because
of the plating voids that occurred due to very bad aspect ratios. The
outgassing which resulted otherwise created what I called "termite hills".
I also had to add a full compliment of topside heater and close up the
preheat tunnel to get enough heat into the assembly without charring the
bottomside.
Good luck,
Phil
ps: if you have press fit already, then eliminate the wavesolder
altogether and SMT or hand solder the rest.
At 07:36 AM 10/4/2008, Werner Engelmaier /* wrote:
> Hi 'bogert4',
>Telling us that the "one single bottom preheater set
>at 350C" is meaningless–even with length of preheater and belt speed
>given it is essentially meaningless. You need the temperature measured on
>the PCB at both surfaces.
>Having said that, you definitely need a preheater on top as well. With one
>prehater only the PCB will warp due to the thermal gradients. Further,
>only a relatively short section near the bottom will have a solder
>connection. Depending on the application, that may be o.k. or a big problem.
>If you solder Pb-free, the situation is worse Td as well as TE(50=>260) is
>more important.
>
>Werner
>
>
>
>
>
>
>
>-----Original Message-----
>From: - bogert <[log in to unmask]>
>To: [log in to unmask]
>Sent: Sat, 4 Oct 2008 7:36 am
>Subject: [TN] Wave soldering temperature profile question
>
>
>
>
>
>
>
>
>
>October 3, 2008Â
>Â
>
>We have an OEM that is wave soldering a 0.125 inch thick backplane assembly.
>Â The assembly contains just press-fit VME connectors (added after wave
>soldering) and some PTH and SMT passive parts (capacitors and resistor
>networks). The SMT parts are hand soldered. Board material is IPC-4101/21,
>24, 26.Â
>Â
>
>The OEM wave soldering machine settings are one single bottom preheater set
>at 350C with solder pot set at 260C. Conveyor speed is 0.9 feet/minute.Â
>Â
>
>Solder is Kester Sn63pb37; flux is Kester 971M; flux applied by foam method.
>Â Solder machine is older Soltec Model 6551.Â
>Â
>
>My question is; for this
>specific application, what is the recommended
>maximum preheat temperature? Seems to me that 350C is too high. Is this
>high a temperature compatible with the Tg of the FR4 board material? Is
>there any concern with damaging the board material from overheating?Â
>Â
>
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