Soldering station with built-in self-calibration function

Details Soldering station with built-in self-calibration function Soldering station with built-in self-calibration function

2002-01-16

2003-06-17

Dunn, Tom (Department: 1725)

Electric heating

Metal heating

For bonding with pressure

C219S241000, C219S229000, C219S238000, C228S055000, C228S009000

Reexamination Certificate

active

06580050

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to soldering irons and soldering stations used in modern electronic production, rework and repair applications which are temperature controlled, but primarily relates to those with closed-loop temperature control for which a defined level of temperature accuracy is desirable, or which are, in certain circumstances, required to be calibrated periodically for the purpose of confirming or re-establishing compliance with various performance standards which include, among other things, proper tip grounding, EMF leakage, temperature stability and a defined level of absolute temperature accuracy between the temperature set or indicated on a control/display device (typically a dial or digital readout) and the actual temperature of the working end of the tip as measured by a more direct, independent means, such as an embedded or spot welded thermocouple, contact pyrometer or some other means.
2. Description of Related Art
For modern, high-reliability electronic production, rework and repair applications, closed-loop temperature controlled soldering irons and stations (hereinafter, “soldering stations” shall also include “soldering irons”) have become the generally accepted norm due to their ability to maintain a safe, appropriate, user-selected tip operating temperature for the particular application at hand. Such traditional soldering stations generally consist of a power supply with a temperature control/display device, typically a dial or digital display which is powered by ordinary line power, and a soldering iron which is connected to the power supply by a power cord and is typically but not always a low voltage supply.
The soldering iron contains a handle and a closed-loop temperature controlled heater to which a replaceable soldering tip is attached through various means, examples of which include the products made by WELLER®, PACE® and HAKKO®. The traditional closed-loop temperature control means may consist of a thermocouple, resistive temperature detector (RTD) or other sensor embedded into the soldering iron heater, a closed-loop resistive control system such as that found in assignee's discontinued product known as the Micro Portable soldering/desoldering system, or other means.
Newer products which feature a combined tip/heater cartridge (for which the entire tip/heater cartridge is changed when the tip wears out) may utilize similar temperature control means or alternatively, may feature a Curie point control, such as the tip/heater cartridge product of METCAL INCORPORATED, or a combined heater/thermocouple arrangement such as that found in U.S. Pat. No. 5,043,560 (Masreliez) and in the Model 941 soldering station of the Hakko Corporation; see also, U.S. Pat. No. 4,839,501 of METCAL® and commonly owned, co-pending U.S. patent application Ser. No. 09/972,194. Compared with traditional soldering stations, tip/heater cartridge stations offer a slim, light weight often cooler handpiece which some operators prefer.
All of these soldering stations, however, suffer from the same or similar problems during use in that their temperature accuracy is less than what may be desired by the user, or that they require periodic calibration to confirm or re-establish compliance with defined performance standards which, among other things, typically include a defined level of temperature accuracy between the desired or selected operating tip temperature, and the true operating temperature (measured at equilibrium or “idle”) as measured at the working end of the soldering tip by some other independent means as discussed above. One such standard for absolute temperature accuracy may be found in ANSI-J-STD-001B (and later revisions) in which “Operator selected or rated temperatures of soldering systems at idle/standby should be within +/−15° C. of actual measured tip temperature.” Of course, users can and often do select different absolute temperature accuracy standards to suit their own particular needs. i.e., the displayed temperature and the actual temperature measured independently at the tip end with an embedded thermocouple must be within +/−15 degrees Centigrade (27 degrees F.) of each other. The conventional or traditional soldering iron systems of PACE® (the assignee of the present application) which employ RTD's provide even better absolute temperature accuracy of within +/−15° F. or better. The RTD itself (which is laser trimmed and consistent) offers a temperature accuracy within 1%, whereas a K type thermocouple (which is often the reference used for calibrating a soldering iron) may be accurate within +/−2.2 degrees Centigrade within a given temperature range (e.g., 0° C. to 277° C.).
These all would certainly represent acceptable levels of accuracy as well as relatively high degrees of accuracy when compared with existing tip/heater cartridge soldering systems whose true operating tip temperature (as measured at the working end of the tip) can vary by as much as 30° F. to 100° F. or more from the set, displayed or “rated” temperature of the tip.
In traditional soldering stations with removable tips, there are a number of reasons why the true operating tip temperature (as measured at the working end of the tip) varies from the user selected or desired tip temperature. The sensor measuring and controlling the heater output is typically located in the heater itself at some point away from the working end of the tip. Thus, it senses temperature changes at that point and only indirectly senses temperature and thermal load changes affecting the working end of the tip. Depending on the circuit configuration of the temperature control system, the relative masses of the heater and tip, the geometry of the tip and the working load on the tip during use, the true operating temperature of the tip (at idle) can vary as much as 50° F. or more from the user selected/displayed temperature on the dial or digital readout. This is particularly evident with large massive tips designed for surface mount component removal. This temperature difference becomes exacerbated when the user selected temperature is increased. It may also be affected when oxides build up between the tip and the heater which inhibits thermal conduction between the two.
Although it is less of an issue for certain types of soldering stations, such as those which use relatively accurate laser trimmed RTD's (Resistance Thermal Detectors), additional unknown sources of error between the user selected/displayed temperature and the true operating tip temperature are introduced when handpieces or heaters are changed, which occurs, respectively, when workshifts change (each shift operator often has his/her own handpiece) or when the heater burns out. This source of error is due to the wide variation in accuracy between sensors (such as thermocouples) from heater to heater. Furthermore, the temperature accuracy of even a single heater can “drift” over time, thus necessitating periodic calibration even if the handpiece, heater or tip/heater cartridge is not changed.
As suggested above, simply changing the tip in a soldering iron can introduce a significant source of inaccuracy between user selected/displayed temperature and the true operating tip temperature. Unless the system features a tip temperature offset feature which compensates for different tip geometries (such as the assignee's MBT 250 product) or the user knows how much error a particular tip will create (and can thus, in some way compensate for it), the user selected/displayed temperature and true operating tip temperature can vary greatly.
In the tip/heater cartridge type soldering stations, different tip geometries can also introduce similar errors. In addition, many of these tip/heater cartridges suffer from the same inaccuracies as traditional soldering iron heaters inasmuch as they employ thermocouples or other temperature regulation means which can greatly vary in accuracy from tip/heater cartridge to tip/heater cartridg

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