Resistance Change Mechanism of Electronic Component Mounting through Contact Pressure Using Elastic Adhesive

Abstract

For mounting electronic components through contact pressure using elastic adhesives, a high contact resistance is an inevitable issue in achieving solderless wiring in a low-temperature and low-cost process. To decrease the contact resistance, we investigated the resistance change mechanism by measuring the contact resistance with various contact pressures and copper layer thicknesses. The contact resistivity decreased to 4.2 × 10^-8 Ω·m² as the contact pressure increased to 800 kPa and the copper layer thickness decreased to 5 µm. In addition, we measured the change in the total resistance with various copper layer thicknesses, including the contact and wiring resistance, and obtained the minimum combined resistance of 123 mΩ with a copper-layer thickness of 30 µm using our mounting method. In this measurement, a low contact resistance was obtained with a 5-µm-thick copper layer and a contact pressure of 200 kPa or more; however, there is a trade-off with respect to the copper layer thickness in obtaining the minimum combined resistance because of the increasing wiring resistance. Subsequently, based on these measurements, we developed a sandwich structure to decrease the contact resistance, and a contact resistivity of 8.0 × 10^-8 Ω·m² was obtained with the proposed structure.

Keywords: contact pressure; contact resistance; flexible electronic device; surface mounting.

Figure 1

(a) Schematic image of electronic component mounting through contact pressure using an elastic adhesive; (b) electrode surface profiles of surface-mounted electronic component; (c) deformation of contact pad of metal layer of elastic adhesive sheet by gradually increasing contact pressure.

Figure 2

(a) Schematic images of experimental sample; (b) optical image of sample.

Figure 3

Optical images of experimental apparatus used to measure the change in contact resistance. (a) Optical image of apparatus; (b) optical image of enlarged view of experimental sample pressed by compression testing machine; (c) optical images of experimental sample with and without pushing.

Figure 4

Schematic image of sample device.

Figure 5

Relationship between contact pressure and contact resistivity with various copper layer thicknesses. The number of trials in each thickness was five.

Figure 6

Relationship between thicknesses of copper layer t_metal, contact resistance R_contact, wiring resistance R_wiring, internal resistance R_internal, and total resistance R_total. Five trials were carried out to measure R_contact for each thickness. Two trials were carried out to measure R_wiring and R_internal for each thickness.

Figure 7

Schematic images and optical images of the (a) simple adhesive structure, (b) concave structure, and (c) sandwich structure.

Figure 8

(a) Comparison of contact resistivity values in simple adhesive, concave, and sandwich structures; (b) flexible electronic device with light emitting diode (LED) chip mounted on a sandwich structure.