You should match the VPS fluid to the alloy being used for optimum condensation performance and thus optimum reflow results. While you can adjust the process to make the "wrong" fluid work, it does not always produce the best results under many conditions, such as CCAs with a heavy mass or large heatsinks, etc. which is the sole purpose of VPS soldering in most cases. So using the "wrong" fluid is sort of defeating the purpose of VPS soldering in the first place.

For one of my client companies, they perform compliant lead attachment to leadless components for extremely high-reliability applications. They use two different machines, one filled with lower temp fluid, and one filled with higher temp fluid for lead-free (or Pb90) applications where they do not want the compliant leads to even approach reflow temps later during reflow of the parts to the board. They tried qualifying a process using the low-temp fluid to solder at higher temps and that did not work at all.

They also tried using the high-temp fluid for the Sn63 application and it sort of worked, but it was immediately evident that the wetting was not as good, but we were not sure just why. I could only assume it was inferior condensation performance, but we didn't really have a method of tracking the condensation except by TC, thus it was an implied conclusion.

The two benefits of using one fluid for both applications is to avoid set-up costs and/or the need to purchase two VPS machines. It might work for commercial purposes, but it certainly did not work for meeting Class 3 consistently. The company invested in a gently-used 2nd VPS machine and has been successfully processing many different and unique applications for years with a 6-Sigma level for the workcenter. 



-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Wettermann

Sent: Saturday, April 15, 2017 2:12 PM

To: [log in to unmask]

Subject: [TN] Shouldn't the Fluid Be Changed for VPhase?



All:



We are running an experiment on the use of vapor phase reflow for a rework process due to the excessive warpage (confirmed by and quantified by Shadow Moire' measurements) of a specific component.We want to keep the temperature  of the component, which is an Sn63 soldered component, as low as possible. The balance of the board is all soldered using a SAC305 alloy.



We are "renting time" on a  local company's VP reflow oven to run the experiments.



Last week went over the DOE and the engineer who is responsible at the company that owns the vapor phase claims that they profile tin lead and lead-free boards using the same fluid in the bed and just adjust the time and heater conditions to get the right profile.



I understood that you were to match the fluid to the solder alloy/liquidus temperature-right?



Being used in the machine is the Solvay S 230  230°C  for unleaded solder (e.g.. SnCuAg)



Comments would be appreciated.

--

Bob Wettermann

BEST Inc

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