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Low-cost direct chip attach: comparison of SMD compatible FC soldering with anisotropically conductive adhesive FC bonding

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7 Author(s)
R. Haug ; Robert Bosch GmbH, Stuttgart, Germany ; R. Behner ; C. -P. Czaya ; Hongquan Jiang
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Small modules on the basis of laminate substrates are often used as a functional subunit in electronic applications. Currently most of them are made by chip and wire technique as one kind of bare chip assembly to fulfill the requirements of size reduction. Low cost flip-chip technology is one of the most promising approaches for further cost and size reduction. In this paper a special car radio submodule is chosen for exemplification. We compare a SMD compatible FC soldering process using eutectic solder bumps and underfilling with an anisotropically conductive adhesive (ACA) FC bonding process using tape or paste materials. FC Soldering: For FC soldering an electroless, maskless Ni/Au plating for under bump metallization (UBM) was chosen. The solder deposition itself is done by stencil printing whereas other cost efficient deposition techniques in the market have been observed. The FC assembly is integrated into a standard SMD line. Different underfill methods for quick underfilling are shown and failure mechanisms and lifetime predictions of assembled flip chips are demonstrated. ACA-FC Bonding: For this process electroless Ni/Au bumping is used as well. An assembly process for ACAs using a semiautomatic FC bonder is developed. In order to reduce the time for mounting the ACA has been precured. The aspects of different process flows including ACA deposition techniques, tape and paste adhesives and filler materials are discussed. The influence of high current, climate, and thermal cycling on the contact resistance and the low frequency noise spectrum is shown. In summarizing this work we describe the benefits and disadvantages of both techniques and discuss the potential for further developments and applications

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IEEE Transactions on Electronics Packaging Manufacturing  (Volume:23 ,  Issue: 1 )