Investigating wire bonding technology applying different printed circuit board platings

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Dr. Krammer Olivér
Department of Electronics Technology

Besides of soldering, wire bonding is the most popular, most versatile and one of the most economical methode for interconnection of currently used electronic components. Wire bonding is the process of attaching microwires to integrated circuits, where two pads are connected by gold, aluminum and more recently copper wires with the diameter of 15 – 500 µm. While promising economic benefit, the move to copper wire is accompanied by technical challenges besides its lower resistivity. While the move to copper wire has promising economic benefit and lower resistivity it is accompanied by technical challenges. These technical challenges are the new pad platings, real-time quality control and the elimination of issues caused by packaging materials. It seems that never before has the interest in wire bonding research been as high as in the past 1 – 2 years.

In the first part of my essay, I made a summary of the three wire bonding technologies, the two kinds of bonding methods and also about the copper wire bonding. I introduced the key problems of applying copper wire and the current solutions for them. In the second part, I detailed the types of pad platings and their metallization process. I summarized the typical properties of board finishes in the dependence of the wire type and also detailed the mechanical bond quality rating techniques and the possibilities of using AOI (Automated Optical Inspection).

The third part of my dissertation contains my practical work. By using the collected information I planned a test board for making tentative bonds. Four terminal sensing of the bonds electrical impedance with the available instrument, pull and shear test of bonds can be carried out on the panels. I examined three kinds of finishes, immersion silver, ENIG (electroless nickel – immersion gold) and ENEPIG (electroless nickel/palladium – immersion gold) with copper wire with diameter of 33 and 300 µm. Quality of the 300 µm copper wire bonds was adequate only on the boards with ENEPIG surface finish. Based on the observations about creation and examination of the bonds, it can be claimed that the ENEPIG layer structure is the recommended plating for heavy copper wire bonding. In contrast with heavy wire, copper wire bonding with 33 µm diameter had similar quality on all three platings. Supposing the same level of reliability, the immersion silver would be the recommended plating for thin copper wire bonding because of its cost-effectiveness.


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