Current-carrying capacity of anisotropic-conductive film joints for the flip chip on flex applications

Authors: Fan, S.; Chan, Y.

Source: Journal of Electronic Materials, Volume 32, Number 2, February 2003 , pp. 101-108(8)

Publisher: Springer

Buy & download fulltext article:

OR

Price: $47.00 plus tax (Refund Policy)

Abstract:

The effect of the substrate-pad physical properties (surface roughness and hardness) on the current-carrying capacity of anisotropic-conductive film (ACF) joints is investigated in this work. Flip chips with Au bumps were bonded to the flexible substrates with Au/Cu and Au/Ni/Cu pads using different bonding pressure. It was found that the current-carrying capacity of ACF joints increased to a maximum value with the rise of the bonding pressure; then, it reduced if the bonding pressure continually increased. The maximum average value per unit area of Au/Ni/Cu pad and Au/Cu pad ACF joints is about 93 µA/µm2 and 118 µA/µm2, respectively, at 100-MPa bonding pressure. The variation trend of connection resistance is the opposite of current-carrying capacity. The variation of current-carrying capacity (or connection resistance) of Au/Cu pad joints is larger than that of Au/Ni/Cu pad joints. The current-carrying capacity is related to the variation of the resistance of ACF joints. The connection resistance of ACF joints depends primarily on the particle constriction resistance (Rcoi), Rcoi ∞ 1/a, where “a” is the radius of contact spot. A smaller contact area results in larger joule heat generation per unit volume (Qg), Qg ∞ 1/a4, which preferentially elevates the temperature of the constriction. The raised temperature increases the resistance because of the temperature-dependent coefficient of the metal resistivity. The theory of tribology is used to explain the difference between Au/Cu pad and Au/Ni/Cu pad ACF joints. For the Au/Cu pad ACF joints, the deformation of the particles’ upper and bottom sides is nearly symmetrical; the contact between conductive particles and pad has the character of “sliding contact,” especially under high pressure. For the Au/Ni/Cu pad ACF joint, the contact between particles and pad determined the conduction characteristics of ACF joints. It has the character of “static contact.” Thus, the current-carrying capacity (or connection resistance) of Au/Cu pad joints is more sensitive to the bonding pressure.

Keywords: Adhesives; anisotropic conducting materials; current-carrying capacity; surface mount

Document Type: Research Article

DOI: http://dx.doi.org/10.1007/s11664-003-0243-7

Affiliations: Email: eeycchan@cityu.edu.hk

Publication date: February 1, 2003

Related content

Key

Free Content
Free content
New Content
New content
Open Access Content
Open access content
Subscribed Content
Subscribed content
Free Trial Content
Free trial content

Text size:

A | A | A | A
Share this item with others: These icons link to social bookmarking sites where readers can share and discover new web pages. print icon Print this page