Paul Vianco - Academia.edu (original) (raw)

Papers by Paul Vianco

New soldering materials and processes have been developed over the last several years to address ... more New soldering materials and processes have been developed over the last several years to address a variety of environmental issues. One of the primary efforts by the electronics industry has involved the development of alternative solders to replace the traditional lead-containing alloys. Sandia National Laboratories is developing such alternative solder materials for printed circuit board and hybrid microcircuit (HMC) applications. This paper describes the work associated with low residue, lead-free soldering of thick film HMC's. The response of the different materials to wetting, aging, and mechanical test conditions was investigated. Hybrid test vehicles were designed and fabricated with a variety of chip capacitors and leadless ceramic chip carriers to conduct thermal, electrical continuity, and mechanical evaluations of prototype joints. Microstructural development along the solder and thick film interface, after isothermal solid state aging over a range of elevated temperatures and times, was quantified using microanalytical techniques. Flux residues on soldered samples were stressed (temperature-humidity aged) to identify potential corrosion problems. Mechanical tests also supported the development of a solder joint lifetime prediction model. Progress of this effort is summarized. * This work was supported by the United States Department of Energy under Contract DE-AC04-94AL85000. Sandia is a multiprogram laboratoy operated by Sandia Corporation, a Locklieed Martin Company, for the United States Department of Energy. blSTRtf3UnON O F THIS DOCUMENT IS UNLIMI $8 DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, express or implied, or assumes any legal liability or mpolnsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

The technology drivers of the electronics industry continue to be systems miniaturization and rel... more The technology drivers of the electronics industry continue to be systems miniaturization and reliability, in addition to addressing a variety of important environmental concems. Surface mount technology (SMT) has evolved in response to these issues. Prototype hybrid test vehicles have been developed at Sandia National Laboratories to evaluate three lead-free solders for Au-Pt-Pd thick f i l m soldering. The alloys are based on the SnAg , SnAg -Bi and SnAg -Bi-Au systems. Populated test vehicles with surface mount devices were designed and fabricated to evaluate actual solder joints. Pastes were screen printed on the test substrates and d o w e d with the components in place. The test components consist of a variety of dummy chip capacitors and leadless ceramic chip carriers (LCC's). The development of the reflow profiles will be discussed. also be presented.

The 91.84Sn-3.33Ag-4.83Bi and 96.5Sn-3.5Ag Pb-free solders were evaluated for surface mount circu... more The 91.84Sn-3.33Ag-4.83Bi and 96.5Sn-3.5Ag Pb-free solders were evaluated for surface mount circuit board interconnects. The 63Sn-37Pb solder provided the baseline data. All three solders exhibited suitable manufacturability per a defect analyses of circuit board test vehicles. Thermal cycling had no significant effect on the 91.84Sn-3.33Ag-4.83Bi solder joints. Some degradation in the form of grain boundary sliding was observed in 96.5Sn-3.5Ag and 63Sn-37Pb solder joints. The quality of the solder joint microstructures showed a slight degree of degradation under thermal shock exposure for all of the solders tested. Trends in the solder joint shear strengths could be traced to the presence of Pd in the solder, the source of which was the Pd/Ni finish on the circuit board conductor features. The higher, intrinsic strengths of the Pb-free solders encouraged the failure path to be located in proximity to the solderhbstrate interface where Pd combined with Sn to form brittle PdSn, particles, resulting in reduced shear strengths. ' Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL8.5000. DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, proccss, or service by trade name, trademark, manufacturer, or otherwise docs not necessarily constitute or imply its endorsement. mommendation. or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

An evaluation was performed which examined the aging of surface mount solder joints assembled wit... more An evaluation was performed which examined the aging of surface mount solder joints assembled with 9 l.84Sn-3.33Ag-4.83Bi solder. Defect analysis of the as-fabricated test vehicles revealed excellent solderability, good package alignment, and a minimum number of voids. Continuous DC electrical monitoring of the solder joints did not reveal opens during as many as 10,000 thermal cycles (O°C, 100"C). The solder joints exhibited no significant degradation through 2500 cycles, based upon an absence of microstructural darnage and sustained shear and pull strengths of chip capacitors and J-leaded solder joints, respectively. Thermal cycles of 5000 and 10,000 resulted in some surface cracking of the solder fillets and coatings. In a few cases, deeper cracks were observed in the thinner reaches of several solder fillets. There was no deformation or cracking in the solder located in the gap between the package I/O and the circuit board pad nor in the interior of the fillets, both locations that would raise concerns of joint mechanical integrity. A drop in the chip capacitor shear strength was attributed to crack growth near the top of the fillet.

The implementation of alternative Pb-free solders has required careful consideration of their imp... more The implementation of alternative Pb-free solders has required careful consideration of their impact on the long-term reliability of electronic systems used in military, space, and satellite applications. One particularly unique case in the high-reliability electronics industry is the use of ceramic substrates – these are the so-called hybrid microcircuit (HMC) assemblies. In these products, ceramic substrates provide better performance under extreme temperature conditions or they are preferred because of the use of high frequency signals within the system. Ceramic substrates include traditional oxide ceramics (e.g., alumina) or one of the newer glass-ceramic substrates (e.g., low-temperature co-fired ceramic, LTCC). Regardless of the particular product, the conductor to which are made the solder joints is often a fired-on thick film layer (10 – 20 µm). Because thick film layers are often comprised of precious metals (Au, Pt, Pd, Ag, either as single elements or as two- and three-co...

Soldering & Surface Mount Technology, 2002

A methodology was developed to establish baseline metrics for assessing the isothermal aging of 6... more A methodology was developed to establish baseline metrics for assessing the isothermal aging of 63Sn‐37Pb (or 60Sn‐40Pb) solder joints in circuit board assemblies. Those metrics were the intermetallic compound layer thickness at the Sn‐Pb solder/Cu interface and the Pb‐rich phase particle size distribution in the solder. The baseline, or as‐fabricated, values for these metrics were 0.71±0.27 μm and 3.2±6.5×10−6 mm2, respectively. The rate kinetics were determined for growth of the intermetallic compound layer and coarsening of the Pb‐rich phase particles by isothermal aging experiments. The/were: (1) intermetallic compound layer thickness (μm)=0.714+ 3.265×103 t0.58 exp(−52200/RT); and (2) Pb‐rich phase particle size (mm2)=3.2×10−6+1.47× 10−3 t0.32 exp(−31000/RT).

Metallurgical and Materials Transactions A, 2006

ABSTRACT Dissolution and intermetallic compound (IMC) layer development were examined for couples... more ABSTRACT Dissolution and intermetallic compound (IMC) layer development were examined for couples formed between 99.9 silver (Ag) and molten 95.5Sn-3.9Ag-0.6Cu (wt pct), 99.3Sn-0.7Cu, and 63Sn-37Pb solders, using a range of solder temperatures and exposure times. The interface reactions that controlled Ag dissolution were sensitive to the solder composition. The Ag3Sn IMC layer thickness and interface microstructure as a whole exhibited nonmonotonic trends and were controlled primarily by the near-interface solder composition. The kinetics of IMC layer growth were weakly dependent upon the solder composition. The processes of Ag dissolution and IMC layer growth were independent of one another.

Materials Science and Engineering: A, 2005

Solid-state interface reactions were investigated when Cu-Fe alloy leads were attached to an elec... more Solid-state interface reactions were investigated when Cu-Fe alloy leads were attached to an electroplated Au layer using 50In-50Pb (wt.%) solder. Two Au layers of different plating process quality were studied. The annealing temperatures were 70, 100, 135, and 170 • C and the times were 1-2000 h. The dominant reaction layer was a composite of (Au, Cu)In 2 IMC and Pb-rich phases. A Au 9 In 4 layer remained <2 m in most specimens. Linear rate kinetics (0.8 < n < 1.2) were observed, indicating an interface-controlled mechanism. The mean apparent activation energy, H, was 56 < H < 73 kJ/mol. The Au 9 In 4 , layer growth kinetics parameters were 0.5 < n < 0.9 and 45 < H < 80 kJ/mol, respectively, suggesting a contribution by grain boundary diffusion. Annealing at 100 • C caused significant degradation to the interconnections through extensive void growth, more so for the poor plating process. Void development began with small Kirkendall voids at the In-Pb/Au interface caused by differing diffusion rates of Au and In through the IMC layer. That initial process was sensitive to the Au layer quality. Void enlargement was caused by a dissociation of the (Au, Cu)In 2 IMC and Pb-rich phases in the absence of Au flux; this process was insensitive to Au layer quality.

Journal of Electronic Materials, 2009

New Pb-free alloys that are variations of the Sn-Ag-Cu (SAC) ternary system, having reduced Ag co... more New Pb-free alloys that are variations of the Sn-Ag-Cu (SAC) ternary system, having reduced Ag content, are being developed to address the poor shock load survivability of current SAC305, SAC396, and SAC405 compositions. However, the thermal mechanical fatigue properties must be determined for the new alloys in order to develop constitutive models for predicting solder joint fatigue. A long-term study

Journal of Electronic Materials, 2004

Compression creep tests were performed on the 95.5Sn-3.9Ag-0.6Cu (wt.%) solder. The specimens wer... more Compression creep tests were performed on the 95.5Sn-3.9Ag-0.6Cu (wt.%) solder. The specimens were aged prior to testing at 125°C, 24 h or 150°C, 24 h. Applied stresses were 2-40 MPa. Test temperatures were Ϫ25°C to 160°C. The 125°C, 24-h aging treatment caused the formation of coarsened Ag 3 Sn particle boundaries within the larger ternary-eutectic regions. The 150°C, 24-h aging treatment resulted in contiguous Ag 3 Sn boundaries in the ternary-eutectic regions as well as a general coarsening of Ag 3 Sn particles. The 125°C, 24-h aging treatment had only a small effect on the strain-time curves vis-à-vis the as-cast condition. Negative creep was observed at 75°C for time periods Ͼ10 5 sec and stresses of 3-10 MPa. The creep kinetics exhibited a sinh term (stress) exponent, p, of 5.3 Ϯ 0.6 and an apparent-activation energy, ∆H, of 49 Ϯ 5 kJ/mol when data from all test temperatures were included. A good data correlation was observed over the [Ϫ25-125°C] temperature regime. Steady-state creep kinetics exhibited a greater variability in the [125-160°C] regime because of the simultaneous coarsening of Ag 3 Sn particles. The aging treatment of 150°C for 24 h resulted in a more consistent stress dependence and better reproducibility of the creep curves. Negative creep was observed in samples aged at 150°C for 24 h when tested at Ϫ25°C, 25°C, and 75°C. The values of p and ∆H were 4.9 Ϯ 0.3 kJ/mol and 6 Ϯ 5 kJ/mol, respectively. Only a slight improvement in the data correlation was observed when the analysis examined separated [Ϫ25-75°C] and [75-166°C] temperature regimes. Creep testing did not cause observable deformation in any of the sample microstructures.

Legislative and marketing forces both abroad and in the US are causing the electronics industry t... more Legislative and marketing forces both abroad and in the US are causing the electronics industry to consider the use of Pb-free solders in place of traditional Sn-Pb alloys. Previous case studies have demonstrated the satisfactory manufacturability and reliability of several Pb-free compositions for printed circuit board applications. Those data, together with the results of fundamental studies on Pb-free solder materials, have indicated the general feasibility of their userange of present-day, electrical components.

Welding Journal, Apr 1, 2019