The patent's assignee is
News editors obtained the following quote from the background information supplied by the inventors: "The present invention relates to resistance trimming for thermistors and, more particularly, to automated resistance trimming after soldering.
"A thermistor is a temperature-sensing element by virtue of the fact that it is a type of electrical component whose resistance varies with temperature. The thermistor comprises a semiconductor ceramic which is pressed, cast, molded, or otherwise formed into a substrate in the shape of a block or cylinder, for example. The thermistor may be formed of a polymer, as well. Contacts are added to the substrate. The thermistor undergoes thermal changes during the addition of the contacts. Thus, an aging process is typically undertaken to allow the resistance characteristic of the thermistor to stabilize. Leads are soldered to the contact surface, generally resulting in the solder covering the entire contact surface. While the process does not cause any problem with respect to physical connection of the leads to the contact, it can present other issues related to additional thermal changes and trimming requirements. With respect to thermal changes, the soldering process necessitates another aging process to stabilize the thermistor's resistance characteristics. With respect to trimming, if the resistance characteristics of the thermistor were exactly as needed at this stage, the process would be complete but more commonly, the resistance characteristics are not as needed. In such situations, trimming of the contact surface is needed to achieve the desired resistance value and tolerance requirements.
"Trimming the contact surface (reducing contact size) to adjust the resistance (increase resistance value) has presented issues with regard to convenience and accuracy, among other factors. In one prior approach, resistance of the thermistor was adjusted by laser ablation of the contact surface prior to soldering the leads. However, since as noted above, thermal changes due to the soldering operation will affect resistance, laser ablation prior to soldering is somewhat inefficient with respect to the overall production of the thermistor. Another prior approach has involved adjusting the resistance value after the soldering process by using a manual grinding wheel to grind both the contact surface and bulk ceramic to adjust resistance and refine tolerance. However, this manual approach is time consuming and not readily automated. Finally, although laser ablation through the solder (rather than prior to the soldering process) has been considered, the varying depth of solder across the face of the contact surface makes this approach impracticable."
As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventor's summary information for this patent application: "According to an aspect of the invention, a method of constructing a thermistor includes forming a semiconductor ceramic substrate; coating a surface of the substrate with contact material; applying a solder mask on the contact material, the applying including applying the solder mask to one or more portions of the contact material to leave an exposed area without the solder mask and a masked area with the solder mask; and trimming the contact material at the masked area to adjust a resistance of the thermistor.
"According to another aspect of the invention, a thermistor includes a ceramic substrate; a contact coating a surface of the ceramic substrate; and a solder mask covering a portion of the contact to form a masked area and an unmasked area on the contact.
BRIEF DESCRIPTION OF THE DRAWINGS
"Referring now to the drawings wherein like elements are numbered alike in the several Figures:
"FIG. 1 depicts a thermistor according to an embodiment of the invention;
"FIG. 2 depicts a thermistor according to an embodiment of the invention;
"FIG. 3 is a block diagram of a system to trim thermistor resistance according to an embodiment of the invention;
"FIG. 4 depicts aspects of a process to trim thermistor resistance according to an embodiment of the invention; and
"FIGS. 5-7 illustrate exemplary solder mask areas according to embodiments of the invention."
For additional information on this patent application, see: Geer,
Keywords for this news article include: Electronics, Semiconductor,
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