C.R. Pickering, W.A. Craig, M.F. Barker, J. Cocker, P.C. Donohue and G. Vanrietvelde
Complex mixed metallurgy multilayers require a very robust dielectric to withstand shorting or blistering effects, together with high density for long‐term reliability in humid…
Abstract
Complex mixed metallurgy multilayers require a very robust dielectric to withstand shorting or blistering effects, together with high density for long‐term reliability in humid environments. The development and performance of a new multilayer dielectric which meets these needs is presented here. A dielectric frit chemistry has been developed with a view to eliminating short circuits and blistering induced by the proximity of dissimilar metallurgies on multiple refiring. Appropriate filler technology has also been developed to optimise dielectric density, toughness and laser‐trim properties. High density has yielded excellent HBT (High Bias Temperature) and HHBT (High Humidity Bias Test) performance. Data on multilayer circuit bowing are presented which take account of the interaction of conductor frit and the dielectric on firing. Silver conductor is employed in inner layers to optimise conductivity and cost. A new 1:3 PdAg conductor for termination of components and resistors also permits heavy Al wire bonding with good aged performance. 25 µm Au and 37 µm Al wire bonding is facilitated by gold conductor on dielectric. The laser trim characteristics of a new resistor series on dielectric are described. The materials system has been tested in a complex multilayer structure which, with the use of a new silver via fill conductor, resulted in defect‐free circuits with zero yield loss.
The paper gives a review of the present knowledge of the piezoresistive properties of thick‐film resistors (TFRs) and shows how they have been exploited for the implementation of…
Abstract
The paper gives a review of the present knowledge of the piezoresistive properties of thick‐film resistors (TFRs) and shows how they have been exploited for the implementation of strain‐related physical‐quantities transducers. Two types of device are described in some detail. These achievements were made possible by a proper choice of resistive and conductive pastes and their firing conditions, since only in this case useful piezoresistive properties can be achieved that make TFR strain gauges competitive with metal and semiconductive materials. After examining some correlations between gauge factors, composition and structure of TFRs, new data are presented showing how the strain sensitivities may be changed by varying the peak firing temperature, dwell time and the nature of the chemical elements which diffuse from terminations in the films.
This paper outlines methods and results of wetting, leaching and adhesion analyses on copper thick film conductors over alumina and multilayer glasses after different processing…
Abstract
This paper outlines methods and results of wetting, leaching and adhesion analyses on copper thick film conductors over alumina and multilayer glasses after different processing conditions. The intention is to provide a better background for evaluating and optimising materials and processing conditions in copper thick films and working out quick, reliable and quantitative methods for better characterisation of copper conductors in production. For these reasons the following methods were used: (a) wetting and leaching analyses with a scanning wetting balance, working in nitrogen, (b) pull tests with solder contacts on copper thick film conductors after soldering, ageing and thermal cycling, and (c) some additional surface analyses (REM, EDX, Auger) for a better understanding of copper pastes and their material interactions, when processed under different conditions. The results are summarised under three general aspects: surface structure and wetting of copper thick films, wetting and leaching of various copper thick films after different processing conditions, and finally the influence of different wetting properties of such surfaces on the solder adhesion strength after soldering, ageing and thermal cycling. The results give good insight into the various interactions of copper thick films with their substrate materials and confirm the ability of the described wetting and leaching analyses for these purposes.
J.V. Manca, L. De Schepper, W. De Ceuninck, M. D'Olieslager, L.M. Stals, M.F. Barker, C.R. Pickering, W.A. Craig, E. Beyne and J. Roggen
In this paper, it is shown that the so‐called in‐situ electrical measurement technique is a valuable tool for understanding failure mechanisms in thick film dielectrics. The…
Abstract
In this paper, it is shown that the so‐called in‐situ electrical measurement technique is a valuable tool for understanding failure mechanisms in thick film dielectrics. The technique makes it possible to measure important electrical characteristics of thick film dielectric systems in the temperature range from room temperature up to 900°C. This information is essential to understand failure mechanisms and to optimise the system with respect to quality and reliability. Mainly two electrical properties have been investigated: (i) the electrical resistance of the dielectric as a function of temperature and (ii) the spontaneous electromotive force occurring at higher temperatures between two metal layers with the dielectric in between. A significant result of the work is the observation of a close correlation between the leakage current measured through the dielectric at elevated temperatures, and the ability of the dielectric to resist shorting and blistering effects during the preparation of circuits. Secondly, from in‐situ voltage measurements, it was confirmed that the mixed metallurgy system Au(bottom)‐dielectric‐Ag(top) acts at 850°C as a spontaneous battery, and the battery voltage (i.e., the spontaneous electromotive force) was measured. Depending on the type of dielectric, a battery voltage up to 200 mV between the two metal layers was observed. As a result of this spontaneous electromotive force, blistering occurs. The battery voltage was shown to be much smaller in unmixed metallurgy systems with Ag(bottom)‐dielectric‐Ag(top) or Au(bottom)‐dielectric‐Au(top). However, if an external voltage of 300 mV is applied to such a system during a temperature profile up to 850°C, blisters can also be induced. This shows unambiguously that blistering is a voltage driven effect.
R. Gee and M.V. Coleman
The environmental reliability of Series Q, a system of materials designed for advanced ‘HIC’ circuits, has been studied using three different migration‐resistance tests. —LMRT: a…
Abstract
The environmental reliability of Series Q, a system of materials designed for advanced ‘HIC’ circuits, has been studied using three different migration‐resistance tests. —LMRT: a test which is used to assess the resistance to electrochemical migration of horizontally adjacent, closely spaced conductor tracks in a high‐temperature, high‐humidity environment with a voltage bias present (60°C, 90%RH, 48 VDC). —HHBT: a test which monitors the ability of a dielectric to resist electrochemical migration when vertically adjacent crossover conductor tracks are oppositely biased (85°C, 85%RH, 5 VDC). —HBT: a test which measures how well a dielectric can sustain its resistance to voltage breakdown over extended periods of time during continuous exposure to conditions of high temperature and voltage (150°C, 200 VDC). The results show that the QSil™ and QPIus™ systems, the two materials systems that comprise Series Q, demonstrate excellent performance in all three areas. Predictions of how well circuits made from these materials will survive in their operating ambient over the long term, e.g., twenty years, have been made.
Darko Belavic, Marko Hrovat, Marko Pavlin and Janez Holc
Diffusion patterning is a dielectric patterning technology, which is used in the screen printed thick film technology for higher density multilayer circuits. This technology is…
Abstract
Diffusion patterning is a dielectric patterning technology, which is used in the screen printed thick film technology for higher density multilayer circuits. This technology is suitable for producing lower cost multichip modules and requires a low additional investment in conventional thick film technology production lines. Comparisons of via resolution capability of diffusion patterning versus conventional thick film technology are described and discussed. Preliminary experimental results obtained with a test circuit showed that 200μm lines and 200μm vias could be achieved with acceptable yield and with minimal modification to standard production lines. The electronic circuit for the pressure sensor was designed and realised with the verified technology as a low‐cost ceramic multichip module. A few results of an investigation of some thick film materials, which comprise the “set” of pastes for diffusion patterning technology, are presented.
Details
Keywords
Y.L. Wang, A.F. Carroll, J.D. Smith, Y. Cho, R.J. Bacher, D.K. Anderson, J.C. Crumpton and C.R.S. Needes
Substrates with high thermal conductivity continue to be in great demand for their ability to enable smaller and denser high power circuits. BeO has been used for this purpose for…
Abstract
Substrates with high thermal conductivity continue to be in great demand for their ability to enable smaller and denser high power circuits. BeO has been used for this purpose for many years with thick film materials. However, due to health and environmental concerns with BeO, many manufacturers feel compelled to switch to alternative substrates. This paper will discuss a thick film system consisting of conductors, dielectric, and resistors developed specifically for use with the most likely alternative, AlN substrates. This system will soon find broad use in applications such as power resistors for telecom, optoelectronic submounts, and high‐power automotive applications.
Details
Keywords
Olli Nousiainen, Tero Kangasvieri, Kari Rönkä, Risto Rautioaho and Jouko Vähäkangas
This paper aims to investigate the metallurgical reactions between two commercial AgPt thick films used as a solder land on a low temperature co‐fired ceramic (LTCC) module and…
Abstract
Purpose
This paper aims to investigate the metallurgical reactions between two commercial AgPt thick films used as a solder land on a low temperature co‐fired ceramic (LTCC) module and solder materials (SnAgCu, SnInAgCu, and SnPbAg) in typical reflow conditions and to clarify the effect of excessive intermetallic compound (IMC) formation on the reliability of LTCC/printed wiring boards (PWB) assemblies.
Design/methodology/approach
Metallurgical reactions between liquid solders and AgPt metallizations of LTCC modules were investigated by increasing the number of reflow cycles with different peak temperatures. The microstructures of AgPt metallization/solder interfaces were analyzed using SEM/EDS investigation. In addition, a test LTCC module/PWB assembly with an excess IMC layer within the joints was fabricated and exposed to a temperature cycling test in a −40 to 125°C temperature range. The characteristic lifetime of the test assembly was determined using DC resistance measurements. The failure mechanism of the test assembly was verified using scanning acoustic microscopy and SEM investigation.
Findings
The results showed that the higher peak reflow temperature of common lead‐free solders had a significant effect on the consumption of the original AgPt metallization of LTCC modules. The results also suggested that the excess porosity of the metallization accelerated the degradation of the metallization layer. Finally, the impact of these adverse metallurgical effects on the actual failure mechanism in an LTCC/PWB assembly was demonstrated.
Originality/value
This paper proves how essential it is to know the actual LTCC metallization/solder interactions that occur during reflow soldering and to recognize their effect on solder joint reliability in LTCC module/PWB assemblies. Moreover, the adverse effect of using lead‐free solders on the degradation of Ag‐based metallizations and, consequently, on board level reliability is demonstrated. Finally, practical guidelines for selecting materials for second‐level solder interconnections of LTCC module are given.
Details
Keywords
T. Kwikkers, J. Lantaires, R.B. Turnbull, H.T. Law, Barry George and Dave Savage
On 20 April ISHM‐Benelux held its 1988 Spring meeting at the Grand Hotel Heerlen. This meeting was totally devoted to implantable devices, in particular to the technologies used…
Abstract
On 20 April ISHM‐Benelux held its 1988 Spring meeting at the Grand Hotel Heerlen. This meeting was totally devoted to implantable devices, in particular to the technologies used for these high reliability, extremely demanding devices. For this meeting ISHM‐Benelux was the guest of the Kerkrade facility of Medtronic. Medtronic (headquartered in Minneapolis, USA) is the world's leading manufacturer of implantable electronic devices. Apart from the assembly of pacemakers and heart‐wires, the Kerkrade facility acts as a manufacturing technology centre for Medtronic's European facilities.
I. Storbeck, G. Leitner, M. Wolf, P. Gottschalk and U. Schläfer
An attempt is made to discuss the adhesion of thick film conductors on ceramic substrates in connection with thermally induced internal stresses caused by mismatch of the thermal…
Abstract
An attempt is made to discuss the adhesion of thick film conductors on ceramic substrates in connection with thermally induced internal stresses caused by mismatch of the thermal expansion coefficient of the various layers and the substrate. The curvature of the bent substrates was taken as a measure of the internal stresses. A theoretical multilayer model is proposed for description of the composite — substrate/conductor/solder/intermetallic phases. This permits estimation of the stresses and the Young's modulus within the layers and explains the decrease of adhesion of the soldered copper layer after ageing.