George has described the saturated VPR process well. The problem with the saturated process is the rapid ramp rate - up to 200C/second - which can lead to increased tombstoning. Some machine suppliers have adopted different strategies to overcome this. You need to discuss with your partner to understand his specific machine's process. The different strategies may well depend on heating rate or insertion depth/speed. Be aware that some of the claims made for these approaches can appear somewhat contradictory . e.g. an unsaturated process zone cannot be truly anaerobic (but this may not matter).

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Regards


Mike 

www.chrisfennerfund.org  
www.facebook.com/chrisfennerfund/  

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of George Wenger
Sent: Saturday, April 15, 2017 11:17 PM
To: [log in to unmask]
Subject: Re: [TN] Shouldn't the Fluid Be Changed for VPhase?

Bob,

I'm not sure if the claims the VP company gave you are correct.  T isn’t unusual for a company using VP to use the same fluid for both tin-lead solder and Pb-Free solder.  Time in the saturated vapors is the determining factor on what the maximum temperature the product (i.e., PCB and components) will reach but adjusting the heater conditions makes no sense at all.  One needs to remember that the basics of VP ( I prefer calling it condensation soldering) is that you heat a fluid and cause it to boil creating a saturated vapor and a set of condensing coils at the top of the container condenses the saturated vapor and the condensed fluid drops back into the boiling sump to be re-boiled; thus  you have a reservoir of saturated vapors into which the product is transported.  The saturated vapor condenses on the product and releases it's heat of vaporization and the part heats up rapidly and uniformly.  The temperature of the product (i.e., the product heating profile) increase exponentially and asymptotically approaches the temperature of the saturated vapor.  To minimize the maximum product temperature you control the amount of time the product is in the saturated vapor.  Adjusting the heater conditions does not adjust the temperature profile; you either have enough heater power to maintain the saturated vapor reservoir when the product is immersed into the saturated vapor (which is the condition you want) or you decrease the heater power to the point the saturated vapor reservoir decreases when the product is immersed into the saturated vapor (which is not the condition you want because the lack of vapor condensing on the condensing coils at the top of the reservoir will cause a rapid loss of the expensive VP fluid and the process would be too expensive to continue running.


Regards,
George Wenger
Failure Signature and Characterization Lab LLC
(732)-309-8964 (Mobile)



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Wettermann
Sent: Saturday, April 15, 2017 3:12 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
[log in to unmask]
Cell: 847-767-5745