The effects of chip and substrate thickness on the reliability of ACA bonded flip chip joints

Abstract

PurposeThe purpose of this study is to investigate the effect of chip and substrate thickness on the thermal cycling reliability of flip chip joints assembled with anisotropic conductive adhesives (ACA) on FR‐4 substrates.Design/methodology/approachFour test lots were assembled with two substrates and two test chips. The thicknesses of the substrates were 710 and 100 μm and the thicknesses of the chips were 480 and 80 μm. To study the effect of the bonding pressure each test lot contained four test series bonded with four different bonding pressures. The reliability of the test samples was studied using a temperature cycling test.FindingsThe reliability of the test lots varied widely during the test. The test lot with a thin substrate and thin chip demonstrated considerably better reliability than the other test lots. In addition, the test lots had different failure mechanisms. After the test delamination was found in every test lot except the one assembled with the thin chip and the thin substrate.Originality/valueThe work shows that the thermal cycling reliability of ACA flip chip joints can be markedly increased by using thinned chips or reducing the thickness of the substrate.

Reliability of ACF Interconnections on FR-4 Substrates

“…This clearly improved reliability as has been reported in [17]. The thinner substrate also decreased the calculated shear stresses in the structure.…”

Study of Structure and Failure Mechanisms in ACA Interconnections Using SEM

“…Its effect on the interconnection structures was studied using cross-sections and SEM (Frisk & Kokko, 2006). During the bonding process the depression of the copper pads into the RCC was found to be much stronger than the depression into the FR-4 substrate.…”

“…Deformation of substrate in ACA interconnections was studied using cross-sections and SEM (Frisk & Kokko, 2006;Frisk & Cumini, 2009;Frisk et al, 2010). SEM has proven to be a very effective method for such studies as the different materials and their interfaces may be clearly seen.…”

“…The deformation of the rigid nickel particles during the bonding process is less than that of the soft particles and the contact area formed is smaller. However, if the bonded contacts are m a d e o f s o f t e r m e t a l , s u c h a s g o l d o r c o p p e r , t h e s e c o n t a c t s d e f o r m d u r i n g b o n d i n g increasing the contact area with the rigid particles (Divigalpitiya & Hogerton, 2004;Yim & Paik, 1998;Frisk & Ristolainen, 2005;Frisk & Kokko, 2006).…”

“…This decreases the shear stress in the interconnection reducing the delamination and increasing the reliability. ACA interconnections with rigid FR-4 substrate were exposed to thermal cycling between -40 °C and +125 ºC (Frisk & Kokko, 2006). When the failed test samples were studied using SEM, delamination was found in several test samples after testing.…”