|Ask the Experts|
December 20, 2019
Idle Wave Solder Temperature
When our wave solder system is not in use, including after the workday and over the weekend, should we maintain the wave solder pot at a specific temperature?
If we allow the solder to cool to room temperature, then reheat to soldering temperature through many cycles, does it change the characteristics of the solder or the solder properties? What is the most common practice?
|Expert Panel Responses|
Our experience with both wave pots and Hot Air Solder Levelers has been that when we intend to have them idle for an extended period, such as a weekend, we allow them to cool to room temperature.
We have not experienced adverse effects from this, and have been following this practice for decades. We do regular analysis of the pot to ensure that the solder alloy is controlled.
Minco Products Inc
There are two significant downsides to cooling the pot below the solidification temperature:
For nights/weekends, keep it just above the melting point.When starting up, first bring the pot back to normal operating temperature, then start the pump and allow the pump to run for 10 minutes prior to running any production. This is necessary to ensure that the pot isre-homogenized; there will be some stratification during the cool-down period,and there may be some collection of solid crystals of IMCs (intermetallic compounds).
It takes 5 minutes or more to re-homogenize the system. At the end of the start-up process, while the pump is still running is an ideal time to pull samples for solder pot analysis, which should be done on a periodic basis. The required interval depends on your specific situation.
It depends (ka-ching) on several factors.
If the exhaust blower shuts off, it is easy for the temperature inside the exhaust to increase due to the heat from the pot not being exhausted fast enough. If it reaches certain temperatures, and the flux residue typically lining the inside of the exhaust flue is flammable, it can ignite.
Not to many things are so bad as to come to work Monday morning, only to discover work isn't here anymore.
In answer to your second question, no degradation of the solder alloy itself occurs due to temperature cycling, as far as I know. However, over time the alloy can change due to drag-out from the thousands or even millions of component leads being soldered. Typically the tin content will drop down, and impurities such as gold, silver, nickel, copper, etc. increase.
It is a very good idea to have a sample removed from all of the solder pots in the building (wave solder,selective solder, tinning pots) and analyzed by your solder supplier to make sure it continues to be compliant to the limits listed in J-STD-006B section 3.3, either quarterly or after X number of hours of machine run time (they almost all have an hour meter inside). This should be part of the preventive maintenance plan (process control plans). You may occasionally need to add a small portion of a bar of pure tin for Sn63 alloy, which typically falls down below the limit.
Calculations based on the amount of solder in the sump and the alloy percentage readings are included in J-STD-006B to help you determine how much to add.It is important, very important, to make sure the bulk alloys you solder and tin with are within specifications, or all kinds of solder defects and reliability issues can result. The periodic analysis will help catch issues such as wrong solder alloy being dumped into the pot (lead-free instead of leaded, or vice versa), and many other little things that cause each day to be filled with joy and optimism for today's solder process engineer.
I would recommend the system be shut down and turned on prior to the start of the shift. Automatic timers can be used to shut down and start up the system. The system can also include the venting system shut down and start up.
As to your question regarding changes in the metallurgy or characteristics of the solder from the system being shuAt down, is an anecdotal position and I've never found any evidence of the alloy changing from the shut down of the system.
As being responsible for 23 wave solder lines while at Digital for over 20 years, this was never an issue.I would say the savings in energy would be substantial over the period of a year from shutting down the system daily and over the weekend. Hope this answers your question.
Vice President, Technical Director
You should also make sure that the solder pot is covered prior to shutting the heaters off. The reason for this is there may be trapped air in the solder and when being reheated the solder can have a explosion which in turn could cause burns to an employee at worst or a large solder spill at least.David Morse, Whelen Engineering
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