You should be able to solder these parts with no problem.
You should get more info from your contract assembler and ask them to optimize the wave process for this board.
1. Depending on the resources at the contract assembler they may have used one of several wave setups for similar boards and possibly did a quick top side temp check with a pyrometer or thermocouple but who knows what location, on laminate or over metal etch areas. If the process requires a selective wave solder pallet was the temperature taken on the body of the part being soldered which is over the opening exposed to solder or did they check an area masked by the wave solder pallet.
2. Some contract assemblers have people that have experienced engineers doing the temperature profile and recognize the trade-offs of conveyor speed and minimize contact time of temperature sensitive parts versus contact time required for thick 20 layer boards with huge parts like power modules. The preheaters can be set to meet the required slope and max temperature.
3. Did your company specify a temperature profiling requirement? Most data loggers have 6 inputs so for large complex boards all 6 thermocouples should be used. Topside board temps should be between 95C and 110C. Are the leads preformed to keep the body off the PCB?
4. I would worry about someone saying the part never exceeds 125C because they measured it and they read 125C on the board.
The preheaters constantly ramp up and loose temp, cycling to maintain the temperature between the tolerance. So if the tolerance is 10% then if the preheater is set to 200C that is a swing of 20C, even with a heat transfer efficiency of 80% that is still a swing of 4C and the solder pot works the same way but with a lower swing but at a higher temperature.
5. What if the body absorbs more preheat energy than the PCB? Did they TC the laminate and the metal etch on the topside that is exposed to the wave and get both numbers. Did they ever epoxy a TCto the component body?
Are the preheaters IR or Convection preheaters? Some IR preheaters are color sensitive, others due to the frequency are designed to heat the laminate, others are designed to heat the metal. Convection heats everything evenly.
6. With the bad economy some contract assemblers use operators or the wave mechanic to set or select an existing wave recipe that should work. They look for solder quality and shorts and that is it.
Some have downsized and no longer have an experienced engineer doing the profiles and therefore the tecch may know the machine but not the component issues, flux specifications, deta T requirements and all the other ramifications.
I would recommend you get a good profile which has 6 thermocouples (TC). One on the ceramic body in the board center as well as one along the side of the board. You should have them optimize the profile to provide a safety margin to allow for the variations.
- The profile of a single board in the wave is not the same as when it is loaded as multiple boards especially where pallets are used will heat sink the machine and cause the heaters to be ramping up and to even have some overshoot. The alarm may not sound depending on how they set the trigger value.
- A very high preheat can help or kill the flux and therefore hurt.
- If the flux is a high temp flux and you absolutely need to go over the normal preheat range, you can always cover the heat sensitive part with a G10 or phenolic block or 3 sided bench shaped block to reduce the heat on that or a bank of parts, as you would with BGAs or Micro BGAs that could be at risk of reflowing if the board is wave soldered.
PS if your not doing PB-free and the board is .092" thick or less, then the temperature of the solder pot could be less.
I hope this info helps you. There are many issues.
Wave soldering is a science or uses many sciences. It is and not as easy as some think if you want good quality and long term reliability.
John Goulet
MFG/Process Engineer
----- Original Message -----
From: "Gerald L Bogert" <[log in to unmask]>
To: [log in to unmask]
Sent: Friday, February 11, 2011 11:48:50 AM
Subject: [TN] Metallized Plastic Capacitors, DSCC Drawing 09006; to hand solder or not to hand solder
February 11, 2011
We have an OEM who wave solders the subject capacitors on circuit card
assemblies. The OEM experienced failures during CCA bench testing. A
sample of parts was sent back to the capacitor manufacturer who
attributed the failure (capacitance value was less than the minimum
value required) to excess temperature during the wave soldering process.
He stated that his parts should be hand soldered not wave soldered. The
soldering profile used by the OEM is set so the top side CCA temperature
is < 125C.
Since the DSCC drawing rates the parts for 125C maximum, and since the
spec also requires 260C dip test for qualification, and since neither
the DSCC drawing nor the capacitor manufacture data sheets indicate his
parts must be hand soldered, I would have expected that the parts could
be wave soldered with no problem.
Does anybody have info on what the worst case capacitor body
temperature might be for the above situation in wave soldering versus
hand soldering? Since these parts are small having two leads on the
bottom surface, during wave soldering, the leads would be exposed to
approximately 260C solder pot temp, but I have no information on what
the worst case cap body temp could be during the normal wave soldering
exposure time. I know that this could be determined by adding TC on the
cap body but I am just looking for some advice on this issue at this
time.
[log in to unmask]
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