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High density flip chip interconnections produced with in-situ underfills and compatible solder coatings

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2 Author(s)
Puhakka, K. ; Lab. of Electron. Manuf., Helsinki Univ. of Technol., Espoo, Finland ; Kivilahti, J.K.

Applicability of three no-flow fluxing encapsulants and one nonconductive adhesive (NCA) to underfilling of high-density flip chip assemblies was studied by bonding Sn37Pb-Bi or Sn-Bi bumped test structures on FR4 substrates. The Sn37Pb or Sn contact pads on the substrates were coated with a thin layer of bismuth. The test chip bump pitches were 250 and 100 μm. The results showed that reliable, intermetallic-free joints can be produced with one of the fluxing no-flow underfills and with NCA together with metallurgically compatible solder coatings. Detailed C-SAM, fine-line focus X-ray, scanning electron microscopy and microanalysis confirmed that metallurgical bonding can be achieved with the fluxing underfill and the NCA, when a thin layer of bismuth top coating is utilized, but only the nonconductive adhesive enables good void-free encapsulation for high density transfusion flip chip attachment. The other no-flow underfills produced numerous voids, especially when the bonding was carried out at such low temperatures as those used for the transfusion bonding

Published in:

Adhesive Joining and Coating Technology in Electronics Manufacturing, 1998. Proceedings of 3rd international Conference on

Date of Conference:

28-30 Sep 1998