Risto Rautioaho

Compositions of MgTiO3-CaTiO3 ceramic with two borosilicate glasses for LTCC technology

Abstract Mixtures of ZnO–SiO 2 –B 2 O 3 /MgTiO 3 –CaTiO 3 (ZSB/MMT-20) and BaO–SiO 2 –B 2 O 3 /MgTiO 3 –CaTiO 3 (BSB/MMT-20) have been investigated as new candidates for LTCC dielectric materials. Two-stage sintering behaviour was observed in both materials, starting at around 600 and 850°C. Nearly full density (97%) was achieved in ZSB/MMT-20 after sintering at 900°C, while a high porosity of 23% was measured in BSB/MMT-20 after firing at 875°C followed by partial melting of samples during sintering at 900°C. After firing, fully crystalline structure with phases of ZnTiO 3 , Zn 2 SiO 4 , Mg 4/3 Zn 2/3 B 2 O 5 and TiO 2 were found in ZSB/MMT-20, while the structure of BSB/MMT-20 consisted of crystalline TiO 2 and BaTi(BO 3 ) 2 and amorphous SiBa(BO 3 ) 2 and SiB 2 O 5 . ZSB/MMT-20 fired at 900 o C showed promising microwave properties having the dissipation factor of 0.001 and a permittivity of 10.6 at 7 GHz. The corresponding values for BSB/MMT-20 fired at 875°C were 0.002 and 8.2, respectively.

Preparation of Nd-doped Ba2Ti9O20 ceramics for use in microwave applications

Densification behaviour, the resulting microstructure and dielectric properties of Nd-doped Ba2Ti9O20-based ceramics were investigated. It was observed that with Nd-doping reaction sintering resulted in lower porosities than with normal two-stage processing. The phases identified at all levels of Nd-doping, for both prefired and reaction sintered materials, namely 0·5, 2·6, 5·0 and 10 wt%, could be classified into three main categories—BaTi4O9 (BT4, Ba2Ti9O20 (B2T9) and the Nd-rich phases. The changes in the dielectric properties caused by Nd-doping can be interpreted as a consequence of the different properties of this Nd-rich phase. Increasing the Nd-content resulted in an increase of the positive temperature coefficient of the resonant frequency, a higher dielectric constant, and also a lower Q-value. Products made without the prefiring stage were found to contain a substantially larger number of flaws and microcracks, and hence are not best suited for use as dielectric materials.

Solder joint reliability in AgPt‐metallized LTCC modules

Purpose – To investigate the effect of the metallization and solder mask materials on the solder joint reliability of low temperature co‐fired ceramic (LTCC) modules.Design/methodology/approach – The fatigue performance of six LTCC/PCB assembly versions was investigated using temperature cycling tests in the −40‐125°C and 20‐80°C temperature ranges. In order to eliminate fatigue cracking in the LTCC module itself, large AgPt‐metallized solder (1 mm) lands with organic or co‐fired glaze solder masks, having 0.86‐0.89 mm openings, were used. The performance of these modules was compared to that of AgPd‐metallized modules with a similar solder land structure. The joint structures were analysed using resistance measurements, scanning acoustic microscopy, SEM/EDS investigation, and FEM simulations.Findings – The results showed that failure distributions with Weibull shape factor (β) values from 8.4 to 14.2, and characteristic life time (θ) values between 860 and 1,165 cycles were achieved in AgPt assemblies in...

Transformation process of laser ablated PZT thin films

Transformation behavior of piezoelectric lead zirconate titanate (PZT) thin films prepared by laser ablation on unheated Al2O3 substrates was investigated within a broad temperature region. As-deposited films were mainly amorphous containing some microcrystalline perovskite and pyrochlore phases. The rhombohedral perovskite was the main phase in the films annealed between 500 and 800°C. These films also contained some pyrochIore, PbTiO3, PbO, and ZrO2. The PbO and ZrO2 disappeared in the optimal annealing temperature interval of 700 to 800°C. Decomposition reactions took place above 800°C due to evaporation of lead and diffusion reactions occurred between substrate and film so that the films annealed at 1100°C consisted of ZrO2, TiO2, and PbO.

Interfacial reactions between Sn‐based solders and AgPt thick film metallizations on LTCC

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 mechan...

Thermal fatigue and metallurgical reactions in solder joints of LTCC modules

Abstract The fatigue behaviour of solder joints in ceramic LTCC modules on FR-4 boards was investigated using thermal fatigue experiments at temperature intervals of 0 – 100°C and −40 – 125°C, and non-destructive and SEM/EDS investigations of thermally cycled modules. Dissolution reactions and formation of tin-based intermetallics were encountered in the joints and found to cause degradation in them. A high peak reflow temperature in the fabrication of modules had a detrimental effect on performance. Vias filled with silver located under the central regions of the solder pads of the LTCC modules enhanced the reliability of the solder joints.

Screen-printed superconducting BiCaSrCuO thick films on ceramic substrates

Abstract The fabrication of BiCaSr CuO thick films on yttrium stabilized ZrO 2 (YSZ), Al 2 O 3 , and MgO substrates was studied to investigate the effect of processing parameters and substrate materials on the properties of the films. Films were screen-printed or cemented. The paste was made of a bulk material, with a nominal composition BiCaSrCu 2 O x , which consisted mainly of two superconducting phases with transition onsets near 115 and 85 K, and zero resistivity at 80–82 K. The films were studied by X-ray diffraction, optical microscopy, scanning electron microscopy, electron microprobe analysis and scanning transmission electron microscopy. Resistivity measurements were also carried out. To achieve good adhesion, density and transport properties, liquid-phase sintering was needed. Films on Al 2 O 3 reacted strongly with the substrate. They showed no zero resistivity. Films printed on YSZ and MgO consisted of a matrix of the high-and low-temperature superconducting phases, some Ca 2 CuO x and Ca 2 SrCu 6 O x , On YSZ there was an interfacial layer of a CaSrZr oxide. The best films on MgO and YSZ had T c ( A = 0) at 81 and 76 K, respectively.

Characterization of Sn7In4.1Ag0.5Cu solder in lead‐free composite solder joints of LTCC/PWB assembly

Purpose – The purpose of this paper is to present a novel Sn7In4.1Ag0.5Cu/Plastic Core Solder Ball/Sn4Ag0.5Cu composite solder joint configuration for second‐level ball grid array (BGA) interconnections of low temperature co‐fired ceramic (LTCC) modules and the thermal fatigue durability of the configuration. The purpose of using the Sn7In4.1Ag0.5Cu solder was to increase the creep/fatigue resistance of critical regions on the LTCC side of the joint.Design/methodology/approach – Test LTCC module/printed wiring board (PWB) assemblies were fabricated and exposed into temperature cycling tests over the 0 to 100°C and −40 to 125°C temperature ranges. The characteristic lifetimes of these assemblies were determined using DC resistance measurements. The failure mechanisms of the test assemblies were verified using scanning acoustic microscopy, FE‐SEM, and SEM investigation.Findings – The test assemblies were exposed to thermal cycling tests (TCT) over test ranges of 0 to 100°C and −40 to 125°C, and characterist...

Compositional and structural behaviour of screen-printed pzt thick films during rapid sintering

Abstract Abstract Lead zirconate titanate (PZT) thick films with a thickness of 10 μm were subjected to rapid open-air sintering and the compositional and structural characteristics were investigated. The results show that the evaporation of lead not only alters the sintering characteristic of thick films, but also causes the formation of separate phases from the bulk PZT. The activation energy for the evaporation process is about 2 eV which is higher than that for self-diffusion of lead. The rapid open-air sintering is in fact a competitive process in which both sintering and evaporation are present. Moreover, the titanium and zirconium exhibit different diffusion features during rapid sintering: titanium tends to diffuse into alumina substrates but zirconium is rejected by the substrates, which causes the composition of films to shift towards the tetragonal phase. The diffusion of aluminium into PZT was also observed, which caused the formation of an unknown phase above 1200 °C.

Thermomechanically loaded lead‐free LGA joints in LTCC/PWB assemblies

Purpose – The purpose of this paper is to investigate the feasibility of using land grid array (LGA) solder joints as a second‐level interconnection option in low‐temperature co‐fired ceramic (LTCC)/printed wiring board (PWB) assemblies for telecommunication applications. The characteristic behaviour of two commercial lead‐free solder materials (Sn4Ag0.5Cu and Sn3Ag0.5Cu0.5In0.05Ni) in reflow processes and thermal cycling tests are also evaluated.Design/methodology/approach – The effect of the reflow temperature profile on voiding in two lead‐free solders in LTCC/PWB assemblies was investigated using X‐ray and scanning electron microscopy (SEM) investigations. The test assemblies were fabricated and exposed to a temperature cycling test (TCT) in a 0‐100°C or −40 to 125°C temperature range. Organic PWB material with a low coefficient of thermal expansion (CTE) was primarily used. In addition, to compare LGA assemblies with low and high global thermal mismatches, an LTCC module/FR‐4 assembly was also fabric...