Mechanical Properties and Interface Microstructure of SAC305 Solder Joints Made to an Ag-Pd-Pt Thick Film Metallization: Part 1—Processing Effects

The processibility was document for interconnections made between the 96.5Sn-3.0Ag-0.5Cu (wt.%, abbreviated SAC305) Pb-free solder and an Ag-Pd-Pt thick film conductor on an alumina substrate. The Sheppard’s hook pull test was used to assess the solder joint strength. Microanalysis techniques documented the corresponding microstructures. Excellent solderability was observed across the process parameters defined by the soldering temperatures of 240–290°C and soldering times of 15–120 s. Molten SAC305 solder dissolved the Ag-Pd-Pt thick film, leading to the precipitation of Ag (trace of Pd) and (Pd, Pt)xSny intermetallic compound (IMC) particles upon solidification. The mechanical strengths of the solder joints were excellent (10–15 N) and remained largely insensitive to the processing conditions. The failure mode was ductile fracture in the solder. These findings confirmed that the SAC305 solder/Ag-Pd-Pt thick film interconnection system had the necessary process window for use in high reliability, hybrid microcircuit (HMC) applications.

Development of YBCO soldered stacked conductor for current lead application

YBCO is currently one of the most widely used second-generation high temperature superconducting (HTS) materials. Compared with the first-generation HTS materials represented by BSCCO, the application of YBCO on the current lead can effectively reduce the 4K thermal load and achieve better stability. This paper introduces the research progress of YBCO soldered stacked conductor based on 65 [Formula: see text]m thickness YBCO film conductor with copper stabilizing layer. The electrical properties of the soldered stacked conductor, including the self-field dependence of the critical current, were tested and analyzed. In this paper, the thermal conductivity of the conductors at 4K is also tested by experimental platform based on GM cryocooler. The differences between superconducting stacked conductors in current lead applications and magnet applications were discussed.

Electrical capacitance of resistive film in plane-layered medium

The parasitic capaciences of film resistors can dramatically affect the output parameters of a microelectronic unit. A technique for computation of these capacitances is necessary for construction of mathematical models for CAD which are to be employed at the stage of circuit simulation, this stipulating the actuality of developing the technique for computations of the capacitances. The article presents analytic expressions for the capacitance of a current-carrying rectangular high-resistance film conductor (resistor), i. e., resistor stripe. The expressions describe the dependence of the capacitance on a non-uniformity of the charge distribution along the vector of the current density. The bounds within which the resistor’s capacitance changes with the ultimate change of the load resistance from 0 to ¥ are found. The estimation of the error caused by a computation of a resistor’s capacitance using formulae intended for a computation of a conductor capacitance is presented. A substantial nonlinearity of the input impedance of the film resistor is revealed. The nonlinearity is caused by a charge redistribution which takes place if the film resistor’s load resistance changes during the functioning of the integrated circuit.

Mechanical properties of polydopamine (PDA) thin films

ABSTRACTPolydopamine (PDA) is a biopolymer, which can form uniform thin films on almost all solid substrates as well as at the liquid/air interface. Carbonized polydopamine possesses graphite-like structure and exhibits high electrical conductivity, which makes it a potential carbon-based thin film conductor. However, studies on mechanical behavior of PDA and its derived materials are very limited. In this study, PDA samples were synthesized through self-assembly of dopamine in aqueous solution. Elastic modulus of thin films was measured using the nanoindentation technique. It is shown that the Young’s modulus of PDA thin film increased with increasing heat treatment temperature (up to 600°C). Doping with Cu ions also increased the Young’s modulus of PDA. Furthermore, all PDA thin films, with and without Cu, exhibited creep behavior.

Evaluation of Ceramic Substrates for High Power and High Temperature Applications

Ceramic substrates with thin film and thick film conductor traces are widely used in microelectronic packages for high temperature operation. In high power applications where the maximum current in the package may be hundreds of amperes, much thicker conductive traces are normally required. For such applications, Direct Bonded Copper (DBC), Direct Bonded Aluminum (DBA) or Active Metal Bonded (AMB) substrates are good candidates. These substrates provide low electrical resistance and high ampacity, thereby enable the design of high power circuits for high temperature operation. The most commonly observed failure mode in these substrates is the delamination of metal layer from the ceramic. The lifetime of a ceramic substrate can be significantly reduced by the processing conditions such as maximum process temperature, and the process gases that the substrates are exposed to. It has also been shown that the propagation of cracks in the ceramic can be abated by dimpling the metal layers along edges and corners. In order to evaluate the effectiveness of these types of substrates for power applications, substrates with various combinations of metal thicknesses and ceramic composition (Al2O3 and AlN) were evaluated for delamination as a function of thermal shock cycles. These samples included both dimpled and non-dimpled metallization. The samples were thermally cycled between −40 °C and 200 °C. A few of these substrates were exposed to forming gas at 340 °C prior to thermal cycling to imitate process conditions. Sample randomization was performed to provide statistically significant data. After a certain number of thermal cycles, delamination cracks were observed to nucleate and propagate in the substrates. Data regarding the reliability of these substrates as a function of thermal shock cycles is presented in this paper, along with failure mechanisms that are commonly observed. Computer simulations were performed to understand the conditions that lead to delamination cracks, and to estimate the crack growth rates in these substrates.

How Silver Powder Metallurgy Affects the Physical Properties of Low Temperature Firing Silver Conductor

With the implementation of RoHS (the Restriction of Hazardous Substance) Directive banning the use of Lead, Cadmium, Mercury and Hexavalent Chromium, hybrid microelectronic manufacturers are globally embracing the lead free movement. These manufacturers must not only understand the implications of their material choice but must be aware of the interaction between lead free solder alloys and their RoHS compliant thick film materials. It is commonly known that lead free solder alloys process at much higher reflow temperatures than lead containing solder which can directly impact the fired film leach resistance and the loss of adhesion. There are also other concerns; lead free solders alloys generally require a different organic flux system to promote wetting and reflow, but this change may cause a fired film conductor to leach more easily than the flux used in the lead containing solders. The use of lead free solders such as SAC305, SAC405 or 95/5 on a low firing (550–570 °C) pure silver conductor has the tendency of leaching the fired film more readily than conductors containing small amounts of palladium or platinum. Many of these situations provide new challenges for the hybrid circuit manufacturer. There is little information available regarding the effects of the lead free solders on low firing silver thick film conductors. This paper discusses the results of a newly developed Pb and Cd free silver thick film conductor paste with a modified silver powder metallurgy to improve the leach resistance, solder acceptance and adhesion using lead free solder. In addition, the pure silver conductor was fired on top of a low temperature dielectric paste. This conductor was evaluated by comparing lead free solder alloys to traditional tin-lead-silver solder alloys. This study included evaluations based on SEM photos, solderability, leach resistance, and initial and long term adhesions. Results are published describing the difference in behavior between the different solder alloys in conjunction with the different silver powder metallurgy.