Effect of substrate material and thickness on reliability of ACA bonded flip chip joints

Abstract

Purpose -The purpose of this paper is to investigate the effect of substrate material and thickness on the thermal cycling reliability of flip chip joints assembled with anisotropic conductive adhesives (ACA). Design/methodology/approach -Four test lots are assembled using three different substrates. Two of the substrates are made of FR-4. The thicknesses of these substrates are 600 and 100 mm. The third substrate is made of liquid crystal polymers (LCP) and is flexible. With the thicker FR-4 substrate two test lots are assembled using both normal and two-step bonding profiles to study how the bonding profile affects the deformation of the substrate. Four different bonding pressures are used to study the effect of pressure on reliability and the failure mechanism of the ACA joints. The reliability of the test samples is studied using a temperature cycling test. Findings -The reliability of the test lot with the LCP substrate is considerably better than that of the test lots with the FR-4 substrates. Additionally, the thinner FR-4 substrate has better reliability than the thicker FR-4 substrate. The failure mechanisms found varied among the test lots. The effect of the two-step bonding process on the deformation of the substrate is found to be minor compared with the effect of the glass fibres. Originality/value -The work shows that the thermal cycling reliability of ACA flip chip joints is markedly influenced by the thickness and material of the substrate. It is also seen that the substrate used influences the failure mechanisms formed during thermal cycling testing.

Liquid crystal polymer as a substrate material for flip chip ACA interconnections

“…Another important factor is the pliability of the substrate material. If the substrate is pliable it may deform during testing and thus reduce the stresses formed during thermal cycling [8]. Due to the glass fibres the elastic modulus of FR-4 was clearly higher than that of the more flexible LCP and PI.…”

Thermal cycling reliability analysis of an anisotropic conductive adhesive attached large-area chip with area array configuration

“…In addition, further failures were observed to occur later on during testing, after 1400 cycles. It is possible that when using an excessively high bonding force the reliability of ACF joints may be compromised [12] [13]. That is, the conductive particles may be crushed, the assembly may be distorted due to high mechanical stresses or the chip or the substrate may even break.…”

Reliability of adhesive joined thinned chips on flexible substrates under humid conditions

“…Bonding time and temperature were chosen according to the ACF manufacturer's recommendation and results from earlier studies with the same materials [18][19][20]. A bonding pressure of 110 MPa was chosen, since it had been found to give good results for the same adhesive in other studies.…”