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Temperature Endurance Test

Membrane Switch Catalogue - 12681 testing

Test Purpose:

Todetermine the effect of temperature on the bond between the layers of a membraneswitch.In this test we will evaluate switch bodies constructed using a Bergquist HeatSeal spac- er and a pressure sensitive acrylic spacer.

METHOD

Bergquist uses test methodASTM D-1876-72 for measuring peel resistance between the switch layers. Samples are pre- pared using the following spacer materials and cut into one-inch- wide specimens for peel testing:A) .005" Mylar™ polyester film(top) – .009" pressure sensi- tive acrylic spacer – .005" Mylar polyester film (bot- tom). B) .005" Mylar polyester film(top) – .008" HeatSeal spacer – .005" Mylar polyester film (bottom).Three (3) samples of eachconstruction are prepared for test- ing at eight temperatures: -25, 0, 25, 50, 60, 70, 80 and 100°C.Each test specimen is placedin the grips of an Instron Test Machine (see Figure 9) and con- ditioned at the specified tempera- ture for five (5) minutes. The top and bottom layers are then sepa- rated at a rate of ten (10) inches per minute. Achart recorder is used to record load versus dis- placement. The average peel strength of each specimen is determined by measuring load at each half inch of separation until ten (10) readings are taken. Peel strengths are reported in units of pounds per inch width.

SUMMARY

The data demonstrates thatthe peel adhesion of PSAadhesive varies greatly with temperature, while HeatSeal peel adhesion remains relatively stable (see Figure 10). At temperatures exceeding 50°C, PSAis suscepti- ble to delamination through both internal and external stresses inherent in membrane switch con- structions. Examples of these forces are interference fits, differ- ences in coefficients of thermal expansion, and upward force due to connector/tail placement. Any delamination of the switch layers will leave the circuit vulnerable to fluid ingression and/or contami- nation (i.e. electrical failure).

FIGURE 9: Instron Test Machine FIGURE10: Peel adhesion at temperature

Bond Strength vs.Temperature

HeatSeal lbs/in2 Pressure Sensitive Adhesive (PSA) 01 234 5 67 8 -25
(Celsius) ° ° 25 ° 50 ° 60 ° 70 ° 80 ° 100 °

5

Chamber Temperature