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TECHNICAL PAPERS

Effect of RCC on the Reliability of Adhesive Flip Chip Joints

[+] Author and Article Information
Laura K. Frisk

Institute of Electronics, Tampere University of Technology, P.O. Box 692, 33101 Tampere, Finlandlaura.frisk@tut.fi

Kati H. Kokko

Institute of Electronics, Tampere University of Technology, P.O. Box 692, 33101 Tampere, Finland

J. Electron. Packag 129(3), 260-265 (Oct 27, 2006) (6 pages) doi:10.1115/1.2753909 History: Received January 11, 2006; Revised October 27, 2006

A need for higher packaging density and functionality has increased the use of new packaging technologies, which has also caused demand for higher interconnect densities on printed circuit boards (PCBs). Sequential build-up (SBU) processes can be used to meet these demands. In the SBU process, additional dielectric and conductor layers are formed on a core board, which is typically made of FR-4. Microvias are formed on these layers to achieve an electrical connection between them and the core board. Resin-coated copper foil (RCC) is the most widely used dielectric layer in the SBU process. The effect of RCC on the reliability of flip chip joints with anisotropically conductive adhesive film (ACF) was studied. Two substrates were used. The difference between the substrates was RCC laminated on the other substrate. The reliability of the test samples was studied using a temperature cycling test and a constant humidity test. The reliability of the substrate with the RCC was found to be better in both tests. Failure mechanisms were studied after the tests, using optical and scanning electron microscopes. After the temperature cycling, several of the test samples made with two highest bonding pressures showed delamination, which has probably caused the failures. In addition, failures occurred during the changes in the test temperature. These were probably caused by warping of the flip chip package. No delamination was found in the test samples with the lowest pressure. The failures in these series were probably caused by relaxation of the adhesive matrix and by too low deformation of the conductive particles. Several cracks had formed on the FR-4 substrates without the RCC during the temperature cycling. In addition, air bubbles were found in the test samples with the FR-4 substrates without the RCC. Since RCC is a pure resin system, it has a high coefficient of thermal expansion, which may cause problems, especially when large components are attached to it. However, in this study, the RCC was found to increase the reliability of the flip chip joints made with ACF during both temperature cycling and constant humidity testing.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Example of a PCB made with SBU process

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Figure 2

Micrograph presenting the immersion of the pads in the RCC, when 140MPa bonding pressure is used

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Figure 3

Micrograph presenting the immersion of the pads in the FR-4 substrate, when 140MPa bonding pressure is used

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Figure 4

Micrograph presenting the deformation of the rigid nickel particle, when 110MPa bonding pressure and the test board without the RCC is used

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Figure 5

Micrograph presenting the immersion of the rigid nickel particle in the pad and the bump, when 110MPa bonding pressure and the test board with the RCC is used

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Figure 6

Results of the temperature cycling test for test series without RCC

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Figure 7

Results of the temperature cycling test for test series with RCC layer

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Figure 8

Micrograph presenting a typical crack in the FR-4 substrate after the temperature cycling test

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Figure 9

Micrograph presenting delamination in a failed test sample with test board A

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Figure 10

Results after the constant humidity test

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Figure 11

Daisy chain resistance values before and after the constant humidity test

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Figure 12

Micrograph presenting typical delamination between the adhesive and the chip after the constant humidity test

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