Resistor Terms:
Resistor Definitions
'A', 'B', 'C', 'D/E', 'F-L', 'M', 'N', 'O', 'P', 'R', 'S', 'T', 'V-Z'
Resistor Mounting:
Resistor mounting plays a critical role in resistor reliability. Resistor mounting determines how
thermal stress, shock, and vibration are transmitted from the environment, or Printed Circuit Board, to the resistor.
Large resistors should be provided with an adequate means for mounting other than the
leads. In the presence of vibration or shock, lead failure can occur, and the larger the mass
supported by the leads, the more likely leads will fatigue. Sometimes a mounting bracket or clip might be required to secure large high-power resistors. Depending on the bracket material it might also be used as a heat sink for the resistor, solving to issues at once.
Even when vibration or shock is
not a serious problem, ease of assembly and replaceability considerations suggest that large
components be individually mounted. Resistors should be mounted such that the body of
the resistor is restrained from movement relative to the mounting base. Bolt-down
provisions, plastic ties, metal or plastic clips, or adhesives may be used to secure resistors
to the mount base. Also, the heat transfer qualities of the resistor can be enhanced or
diminished dependent on the clamping heat conduction properties of the method used.
Maintain lead lengths to a minimum. Leads transfer heat to Printed Circuit Boards (PCB)
or other mounting provisions, which act as a heat sink. Lead Length vs Heat Dissipation.
Resistor mounting may also be defined in the data sheet. However; mounting to prevent over-heating my contradict mounting requirements due to vibration issues. Component pad sizes of a particular size or shape or thermal vias [High-Power Resistors] may be required for the device to comply with the resistor derating curve provided by the data sheet. Check to insure that mounting instructions are given in the data sheet. Some derating curves may also specify the board type [as in FR4], but this is less common for resistors. Surface Mount resistor packages having a tab [TO-263] may require the tab attachment point [Pad] to be much larger than the actual size of the tab.
Some through-hole resistors may also have a tab to attach a heat sink; Example,
TO-126, TO-220, TO-247 package styles. Large power resistors should be mounted to a metal chassis for heat dissipation.
Surface Mount resistors will also have some mounting information in the data sheet. At the very least the data sheet will indicate the recommended pad size to use on the PCB.
Through-hole Mount resistors almost always dissipate more heat or operate at a higher temperature than a surface mount resistor, but it depends on size, so always refer to the data sheet for the correct data. Mounting recommendations may not be provided in the data sheet for through-hole resistors.
