Rex,
If you have a wave solder that uses contactors you may want to replace them with wetted Mercury devices or SSRs...
Paul
Paul Edwards
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rex Waygood
Sent: Wednesday, September 15, 2010 9:18 AM
To: [log in to unmask]
Subject: Re: [TN] Wave Temperature Overshoot
Thanks for all the inputs.
I think that the problem is cured but we are waiting a bit longer before we celebrate!
The main contactor had one set of contacts that were sticky. We disconnected the set of heaters associated with those contacts and the bath stabilised correctly. The new contactor is now fitted and we are keeping an eye on it.
Regards
Rex
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Goulet
Sent: 15 September 2010 16:10
To: [log in to unmask]
Subject: Re: [TN] Wave Temperature Overshoot
The Electrovert wave solder has a boost heater that turns on along with the standard control heater for when the solder pot is shut down.
In the Electrovert manual you will see that you are supposed to use the provided thermal blanket to cover the solder pot to prevent solder eruptions and reduce heat loss. I think if you were to log the current use, you would find that you aren't reducing cost by allowing the solder pot to cool off to the solid state and then require two heaters to work almost maximum duty cycle to bring the pot back up to temperature every day. The shut down procedure is usually reserved for over the weekend only.
A better method may be to create a low temp recipe "Daily Shutdown" where the solder pot temp is reduced to 363F and the thermal blanket is placed over the pot to further reduce heat loss over the evening and night time hours. The booster heater would not come on, preventing the early failure of this heater, the temperature overshoot should not occur if the thermocouple is clean of dross and where there would be no shrinkage as Paul Edwards referenced. The PID will have a slower ramp up speed and prevent the over shoot. The thermal blanket reduces heat loss and the time to reach the desired pot temperature is greatly reduced and therefore reduces your cost. You may want to consider this process for your daily routine.
- As I recall the Vitronics wave allows you to set the temperature as well as the time for a soft shut down, which we used every day.
John Goulet
Sr. Process Engineer
----- Original Message -----
From: "Paul Edwards" <[log in to unmask]>
To: [log in to unmask]
Sent: Thursday, September 2, 2010 12:29:51 PM
Subject: Re: [TN] Wave Temperature Overshoot
The temperature overshoot is can be caused by and in many cases is caused by the change of the phase of the solder between the heaters and the thermal sensor...As solder cools shrinkage occurs depending on the local thermal gradients and alloy...The shrinkage and local solidification generates separation between the sensing elements and the heaters...These then can cause a decoupling between the sensor and the heaters as the heaters try to liquefy the slurry/solid solder mix causing solder phase separation and voiding in the solder pot...This then forces the heaters to higher power level until the sensor is in full thermal conduction with the heaters... Then the heaters and their attached thermal mass will have to "cool down" to the controller's set point...
Paul
Paul Edwards
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Amol Kane
Sent: Thursday, September 02, 2010 8:37 AM
To: [log in to unmask]
Subject: Re: [TN] Wave Temperature Overshoot
We have the same wave and I have never seen any temperature shoot overshoot. The temperature reading increases to 520F and stays constant at that valve from a cold start. Takes about 3 hours from room temp to reach 520F.
Amol S. Kane
Process Engineer
Catalyst Manufacturing Services
941 Route 38
Owego NY 13827
Office : 607-687-7669 X349
Fax : 607-687-9733
E-mail: [log in to unmask]
??Please consider the environment before printing this e-mail
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Richard D. Krug
Sent: Thursday, September 02, 2010 8:34 AM
To: [log in to unmask]
Subject: Re: [TN] Wave Temperature Overshoot
I'd suggest talking with Electrovert for recommendations on changing PID controller settings.
You've got me thinking about additional cost savings here. We use the timer functions to turn off the solder pot heaters at night and then turn then back on in the morning. We turn on the heaters at 2:00 AM M-F, even when pot may have been off all weekend. Pot always is ready for production at 7:00 AM.
I'm going to record pot temperature for a week to see what actual temperatures are. I may have a temperature overshoot but have never seen it based on our warm up timer settings. A record of actual overshoot could provide insight into PID controller setting changes.
Dick Krug, CSMTPE
SMT Process Engineer
Sparton Corporation
30167 Power Line Road
Brooksville, FL 34602-8299
p (352) 540-4012 (Internal Ext. 2012)
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rex Waygood
Sent: Thursday, September 02, 2010 7:41 AM
To: [log in to unmask]
Subject: [TN] Wave Temperature Overshoot
The following problem is on an Electovert Vectra with SN100C alloy.
Due to a decision to allow the bath to cool over night, to save energy, we are experiencing over temperature shoot for several hours after reaching temperature. Once the overshoot has gone the bath then seems to control OK.
The PID controller for the bath has the same terms in it as it had for SnPb.
If I make an assumption that SN100C is 100% Sn in terms of its Specific Heat then I have 0.244 J/gm/K vs. 0.180 J/gm/K for 60/40 Sn/Pb. (1.36:1) This is a big difference in specific heat.
Intuitively I feel that the SN100C should be less likely to overshoot.
Does anyone have experience of having to have the PID terms adjusted in their wave having changed the alloy in order to maintain temperature?
Has anyone done the arithmetic to show that allowing the alloy to go through a phase change in cooling down is more economic than just keeping it above the phase change point? Again my intuition says it is better to let it cool but I've been asked justify my assumption! :-)
Regards
Rex
Rex Waygood
Technical Manager
Hansatech EMS provides value manufacturing through engineering and
quality
Hansatech EMS Limited
Benson Road
Nuffield Industrial Estate
Poole
Dorset
BH17 0RY
+44 (0)1202 338200
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