Title :
High density flip chip interconnections produced with in-situ underfills and compatible solder coatings
Author :
Puhakka, K. ; Kivilahti, J.K.
Author_Institution :
Lab. of Electron. Manuf., Helsinki Univ. of Technol., Espoo, Finland
Abstract :
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
Keywords :
X-ray chemical analysis; acoustic microscopy; encapsulation; flip-chip devices; integrated circuit bonding; integrated circuit interconnections; integrated circuit packaging; integrated circuit reliability; integrated circuit testing; microassembling; scanning electron microscopy; soldering; voids (solid); 100 micron; 250 micron; C-SAM; FR4 substrates; Sn contact pads; Sn-Bi; Sn-Bi bumped test structures; SnPb contact pads; SnPb-Bi; SnPb-Bi bumped test structures; bismuth coating; bismuth top coating; fine-line focus X-ray analysis; fluxing no-flow underfills; fluxing underfill; high density flip chip interconnections; high density transfusion flip chip attachment; high-density flip chip assemblies; in-situ underfills; metallurgical bonding; metallurgically compatible solder coatings; microanalysis; no-flow fluxing encapsulants; no-flow underfills; nonconductive adhesive; reliable intermetallic-free joints; scanning electron microscopy; solder coatings; test chip bump pitch; transfusion bonding; underfilling; void-free encapsulation; voids; Assembly; Bismuth; Bonding; Coatings; Encapsulation; Flip chip; Nonconductive adhesives; Scanning electron microscopy; Testing; Tin;
Conference_Titel :
Adhesive Joining and Coating Technology in Electronics Manufacturing, 1998. Proceedings of 3rd international Conference on
Conference_Location :
Binghamton, NY
Print_ISBN :
0-7803-4934-2
DOI :
10.1109/ADHES.1998.742009