Thermal resistance measurements are strongly linked to the thermal impact of a given fixture or mounting arrangement for the device-under-test. Generally, the fixturing utilized should mimic the physical mounting of the device for the intended application. For example, if the intended application of the device requires mounting on a PWB, the thermal testing of the part should be performed on a similar PWB; if the intended application of the part includes attachment to a heat sink, the thermal testing should utilize a heat sunk fixture. When planning a thermal test, the fixturing specification is critically important.
Analysis Tech offers a selection of standard fixture types. Although these products will accommodate most needs, there are certainly many situations which will require custom fixturing. The Analysis Tech Thermal Analyzers can be easily connected to custom or "home brewed" fixturing and are readily adaptable to existing fixturing from other manufacturers. The standard test fixtures are described below. Analysis Tech also offers custom fixtures and custom fixture design services to suit any test need.
JEDEC Standard Printed Circuit Board Fixturing
Thermal testing of devices designed to be attached to a circuit board (PWB) should always utilize a PWB test fixture. Analysis Tech offers a collection of JEDEC standard test PWB fixture boards. All of these standard PWBs are fabricated of standard .063" glass epoxy, 2 ounce copper traces, and with 0 to 2 inner copper layers as desired. They are compatible with the PWB fixture connector used in the Still Air Chamber and Servo Controlled Wind Tunnel. PWB test boards can be conveniently configured for any part type with soldered wire jumpers including connections for junction temperature sensing and heating power delivery.
Many test PWBs are designed to accommodate a range of package sizes and lead counts to minimize the number of different PWBs required, and therefore limit the expense and maximize the versatility of our PWB test fixturing. Other, non-Analysis Tech test PWB coupons can be readily adapted to utilize standard Analysis Tech PWB test fixtures. Technical questions on standard and custom PWB fixturing can be addressed by contacting the Analysis Tech factory.
Discrete package, socket-type fixtures
Socket-type test fixtures handle standard discrete packages with low lead counts. Usually these types of fixtures are used exclusively for die attachment testing of devices such as diodes, bipolars, MOSFETS, etc. These fixtures utilize industry standard test sockets combined with a simple enclosure incorporating screw-terminal programming. Each test fixture will handle a specific package regardless of its device-function. Although some standard designs exist, most of these fixtures are custom designs that should be discussed with Analysis Tech engineering staff.
Heat Sunk Fixtures
These fixtures are generally used for thermal measurements referenced to the case temperature (Rjc). They are available as the Air Cooled Rjc Fixture (for up to 60 watts) and the Liquid Cooled Rjc Fixture (for up to 600 watts). The pneumatic clamp mechanism provides accurate clamping pressure. Thermocouple sensors for the underside of the device-under-test are integrated into the cooled surface.