It is important to understand that process verification and equipment calibration are not the same and that some types of equipment do not require calibration but may still require the development of procedures for accurate process verification.
We are often asked questions relating to calibration procedures for the various tools and equipment that we manufacture. These questions are usually asked as a result of the calibration requirements that are specified in many quality assurance program directives. The equipment that we manufacture can be accurately identified as NCR (No Calibration Required) as there are no features within this equipment which allow for calibration.
Many quality assurance programs will alsorequire the development of written procedures to outline accurate methods of verification that can be utilized to monitor the various processes that may be used for an application. Process verification can be accomplished with our equipment by knowing what measurable, variable attributes exist for the specific soldering application being reviewed.
When you are developing the process for any application it is important to identify attributes which are variable in nature that can have a direct effect on the results achieved. Once identified each of these attributes should be measured prior to and monitored during the process development in order to determine and establish an acceptable tolerance level for each of them. The information collected should be well documented in order to help establish the appropriate verification steps that can be followed to monitor the actual process once the development steps have been completed.
Time and temperature will be the two primary variable attributes for you to be concerned with when developing a process for applications using the type of tools and equipment that we manufacture. For the purpose of this document, time will be referred to in two ways; dwell time will refer to the time that is required to heat and flow solder to complete the solder joint, while idle time will refer to the time allowed between solder joints (from the completion of one joint to the beginning of the next) to recover thethermal loss from soldering irons and solder pots and to dissipate the heat accumulated in resistance soldering handpieces.
Soldering Irons
The type of soldering irons that we manufacture is most commonly referred to as a constant temperature soldering iron. These irons are designed to ramp up quickly and then maintain a sufficient operating temperature for continuous soldering applications like joining together seems. They also achieve rapid thermal recovery between non-continuous solder joints.
During the process development stage it will be important to monitor the actual temperature of the soldering iron tip using an independent temperature sensing device. As soon as the tip is hot enough to melt and flow solder the process begins. The more heat that is drawn from the iron while soldering, the longer the required idle time will be to recover thermal loss. As you are developing the process you will be able to determine the appropriate dwell and idle times that will be required to maintain the operating temperature necessary for the application. If the soldering iron can not maintain the appropriate operating temperature, when being given an adequate amount of idle time for recovery,it may be necessary to reevaluate the application to determine a more appropriate tool. If the soldering iron's tip temperature continues to climb well beyond the required operating temperature (once the operator has achieved some level of efficiency) you may want to incorporate an added measure of temperature control (e.g. Voltage Controller (Model 3700)) or choose a smaller or lower wattage iron for the application. Operating an iron at temperatures too far above what is actually required for the soldering that is being performed may be detrimental to both the heating element and the tip and might also cause thermal damage to temperature sensitive components that are being soldered. There is nothing to calibrate within a constant temperature soldering iron. Internal test and evaluation of this method of temperature control indicates the ability to maintain operating temperatures within 5°F of the established set point.
Solder Pots
The current line of solder pots that we manufacture are industrial grade, general purpose pots. These are rugged pots that rely on a simple, bi-metal thermostat to control their operating temperature and are intended to be used in non-critical applications or for general solder dipping and low volume pre-tinning applications.
The recommended operating temperature for a general purpose solder pot is 100-150°F (38-66°C) above the liquidus temperature of the solder alloy that is being used. This is to compensate for the thermal loss that takes place during the soldering application. As you develop the process you will be able to determine the most efficient operating temperature based on the mass and the volume of the materials being introduced into the pot for soldering. While soldering if thermal loss continues below the temperature required to achieve the necessary results, raise the operating temperature of the pot. If the solder pot temperature continues to rise above the required temperature during soldering you will want to adjust the temperature downward. Operating the solder pot at temperatures too far above what is required for an application can be detrimental to the heating elements and can also adversely affect the soldering process.
Excessive heat creates higher levels of dross and oxidation in the solder bath. It also increases the aggressive solution activity of the solder alloy which can accelerate the contamination level within the solder bath.
There is no calibration procedure possible or required for solder pots with this type of thermostat and you can expect to see as much as 50°F of variance from the intended operating temperature. For tighter tolerance requirements a Voltage Controller (Model 3700) can be used to adjust the voltage and more accurately control the temperature of these solder pots.
Internal test and evaluation of this method of temperature control indicates the ability to maintain operating temperatures within 5°F of the established set point.
Resistance Soldering Equipment
The current line of resistance soldering equipment that we manufacture includes power units that range in output levels from 100 watts maximum to 3000 watts maximum and a wide variety of handpieces and accessories for use with them. This type of equipment can be used for soldering or brazing applications ranging from PCB Thru-hole assembly to 3" O.D. thin wall copper tubing. As your process is being developed the goal should be to efficiently create a quality solder joint in a comfortable, repeatable manner.
When you are developing a process that uses resistance soldering equipment the need to establish a specific operating temperature will be replaced with establishing the correct balance of output voltage from the power unit and the dwell time required to properly flow the solder. These are the variable attributes that need to be established and identified for proper set up and ongoing verification of your soldering process. As you increase the level of power, thermal ramping will be more rapid and the dwell time required to flow the solder will be shorter. Once the requirements for power and time have been established they can then be accurately used for future process verification.
To insure the most accurate and consistent process repeatability the use of our Precision Timer Module (Model 105PTM) is recommended to control the dwell time used for the actual soldering process (for applications that do not exceed 1200 watts of required power). This tightens the level of process control and improves the accuracy of process verification as the Precision Timer Module can be set up to control dwell time to within 1/100ths of a second. Because the Timer Module is a multi-function timing device there are many ways that it can be used to control the consistent repeatability of your soldering process.
Although resistance soldering is often utilized to speed up your process, care should be taken not to try soldering too fast as this could cause the joint to overheat before the solder has a chance to flow properly. This can result in the flux burning or the intended joint surfaces oxidizing so they will not accept the solder. Once you have established the most appropriate dwell time, an appropriate idle time must be established. Idle time is not used for thermal recovery but instead is required to allow for cooling of the equipment between solder joints.
There is no calibration required for this equipment; however the output voltage of American Beauty resistance soldering power units is AC and can be monitored or verified using a standard AC Volt-meter or Multi-meter set to read AC voltage. The output voltage of the power unit (during equipment setup or process verification) needs to be measured with no load present to insure accuracy. The established dwell time is also important to maintain and should be verified periodically to insure accurate and consistent repeatability of the established process.