Bondable Wire Process Equipment
Automation Technology’s Bondable Wire Process Equipment can be used as a stand-alone system or incorporated into one of ATI’s Test Systems. This equipment provides the power to heat bondable wire and a unique high speed, extremely accurate, temperature measurement circuit. The combination of these two elements insures accurate and reliable activation of the bonding cement located on the surface of the bondable wire.
The bonding process is accomplished by passing a high DC current through the wire to be bonded. The amount of current and the resistance of the wire determine the power consumed by the wire. This amount of power inversely affects the time required for the bonding cement to reach its activating temperature. Several factors tend to remove heat from the wire and increase this time. These factors would include the wire area in contact with the air or any large mass or “heat sink”. This “Heat Sink” could be an iron or steel core, other windings, or blocking/forming tooling that may be applied to the coil during the bonding process to “block” or “form” the coil. Because the resistance of wire and the applied current may vary and the factors that remove heat from the coil may not always be uniform, wire temperature after the same period of time with the same current applied, will differ from one coil to another. It is therefore, desirable to measure the average wire temperature and use this to determine when to remove power (heat).
This System utilizes a unique method of temperature measurement, which eliminates the problems associated with other methods of temperature measurement. The theory of operation is as follows:
Resistance of the wire before bonding is measured; ambient temperature is also measured and it is assumed the wire temperature at this time is at ambient.
Using the resistance temperature coefficient of the wire, the computer within the system calculates what the resistance of the wire should be when the wire reaches the desired temperature. Once this calculation is made, the bonding process can begin.
The formula calculation is:
RFinal = RInitial + RInitial * T.C.(TFinal – TInitial) where:
R = Resistance, T = Temperature and
T.C. = Temperature Coefficient of Wire (.393%/°C for copper).
See the following example:
The Bonding process functions are as follows:
A high DC current is applied to the coil. While this current is flowing through the wire, or coil, voltage across the wire, or coil is measured. From the measured voltage and measured current, wire resistance is calculated. When the calculated wire resistance reaches the desired value, current is removed.
This method of Temperature Measurement yields the average temperature of the wire, which is far more desirable than the surface temperature, which is exposed to the air.
Given that this method utilizes closed loop control, bonding currents can be very high, resulting in very fast bonding times (i.e., 3 to 5 seconds). Closed loop control provides bonding temperature accuracy and repeatability unattainable with other methods.
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