Characterization of Bond Strength

Packaging is essential for the development of new micro systems and can therefore be considered a key enabling technology. To ensure their functionality, micro electromechanical systems (MEMS) and nano electromechanical systems (NEMS) require a hermetic and mechanically strong package. The reliability of MEMS and NEMS devices is significantly affected by the bond interface.

The knowledge of its mechanical properties is essential for the design of new devices as well as the estimation of their lifetime. For the analysis of the bonding strength, Fraunhofer ENAS uses and optimizes three different test methods: the pull test, the micro-chevron-test and the compression shear test. The micro-chevron-test reproduces one of the most critical failure mechanisms (mode-I-crack opening) and is used to analyze the fracture toughness and energy release rate. Furthermore, the pull test is used for the characterization of the tensile strength of the bonded interface. The compression shear test is often used to analyze packages between heterogeneous materials with different coefficients of thermal expansion. Both pull test and compression shear test can be carried out on fully processed devices, while the micro-chevron-test requires special test geometries.

Advantages of the test method:

• Characterization of bonded interfaces with and without intermediate layers
• Analysis of the influence of different Process parameters on the bonding strength Evaluation of the process homogeneity over the whole wafer/ substrate
• Analysis of fully processed devices by pull and compression shear test

Comparision of test methods:

	micro-chevron-test	compression shear test
Strength	fracture toughness KIC	shear strength tshearr
	energy release rate GIC
Substrates	same material	heterogeneous materials
Bonding technologies	with and without intermediate layers	with and without intermediate layers
accuracy	high	medium
deviation	small	medium
Sample length	l ≥ 5 mm	l ≤ 10 mm
Sample width	5 mm ≤ w ≤ 10 mm	w ≤ 10 mm
Wafer thickness	d ≤ 675 µm	50 µm, 100 µm, 200 µm, 300 µm, 400 µm, 450 µm, 500 µm, 600 µm
Test speed.	v ≥ 1 µm/s (v≥ 0,01 mm/min)	v ≥ 0,01 mm/min
Special geometries and apllication oriented designs can be provided on request
Maximum forcet	Fmax ≤ 80 N (Fmax ≤ 1000 N)	Fmax ≤ 5000 N
Special requirements	Numeric analysis of stress intensity coefficient