Effect of firing conditions on thick film microstructure and solder joint strength for low-temperature, co-fired ceramic substrates
Low-temperature, co-fired ceramics (LTCC) are the substrate material-of-choice for a growing number of multi-chip module (MCM) applications. Unlike the longer-standing hybrid microcircuit technology based upon alumina substrates, the manufacturability and reliability of thick film solder joints on LTCC substrates have not been widely studied. An investigation was undertaken to fully characterize solder joints on these substrates. A surface mount test vehicle with Daisy chain electrical connections was designed and built with Dupont{trademark} 951 tape. The Dupont{trademark} 4569 thick film ink (Au76-Pt21-Pd3 wt.%) was used to establish the surface conductor pattern. The conductor pattern was fired onto the LTCC substrate in a matrix of processing conditions that included: (1) double versus triple prints, (2) dielectric window versus no window, and (3) three firing temperatures (800 C, 875 C and 950 C). Sn63-Pb37 solder paste with an RMA flux was screen printed onto the circuit boards. The appropriate packages, which included five sizes of chip capacitors and four sizes of leadless ceramic chip carriers, were placed on the circuit boards. The test vehicles were oven reflowed under a N{sub 2} atmosphere. Nonsoldered pads were removed from the test vehicles and the porosity of their thick film layers was measured using quantitative image analysis in both the transverse and short transverse directions. A significant dependence on firing temperature was recorded for porosity. The double printed substrates without a dielectric window revealed a thick film porosity of 31.2% at 800 C, 26.2% at 875 C and 20.4% at 950 C. In contrast, the thick film porosity of the triple printed substrates with a dielectric window is 24.1% at 800 C, 23.2% at 875 C and 17.6% at 950 C. These observations were compared with the shear strength of the as-fabricated chip capacitor solder joints to determine the effect of firing conditions on solder joint integrity. The denser films from the higher firing temperatures had correspondingly higher shear strengths. The 0805 chip capacitor had a shear strength of 12.6 {+-} 1.4 lbs. at 800 C, 13.3 {+-} 1.9 lbs. at 875 C and 13.6 {+-} 1.4 lbs. at 950 C for the triple printed substrates with a dielectric window. The trend was similar for the larger capacitors; the 1912's exhibiting shear strengths of 20.5 {+-} 4.8 lbs. at 800 C, 26.2 {+-} 1.7 lbs, at 875 C and 29.0 {+-} 0.2 lbs. at 950 C.
- Research Organization:
- Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Sandia National Lab. (SNL-CA), Livermore, CA (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AC04-94AL85000
- OSTI ID:
- 750205
- Report Number(s):
- SAND99-2826C; TRN: AH200007%%73
- Resource Relation:
- Conference: International Brazing and Soldering Conference, Albuquerque, NM (US), 04/02/2000--04/05/2000; Other Information: PBD: 4 Jan 2000
- Country of Publication:
- United States
- Language:
- English
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