T. Kangasvieri

Design aspects of microwave components with LTCC technique

Abstract Low temperature co-fired ceramic (LTCC) technology, widely used in the automotive industry, is now being employed in microwave applications. Several commercial materials with low dielectric losses at microwave frequencies and adequate thermomechanical properties have been introduced. Computer-aided design of three-dimensional circuits has also become available. These advances together with high-quality manufacturing technology have placed LTCCs at the forefront in the development of miniature microwave devices. The paper outlines LTCC technology placing emphasis on those essentials of the materials and processing technologies about which the microwave circuit designer needs to be aware. The discussion is illustrated by examples.The crucial issue of component reliability is also addressed. Although the integration of passive components into the structure improves reliability, the joints between the LTCC module and PCB remain as significant ‘weak link’. Therefore, thermomechanical and structural design is a key to reliable LTCC assemblies.Finally, some future trends the LTCC technology for microwave applications are outlined.

Broadband BGA-Via Transitions for Reliable RF/Microwave LTCC-SiP Module Packaging

This letter presents two broadband ball grid array-via transition structures applicable in reliable radio frequency/microwave low-temperature co-fired ceramic system-in-package (LTCC-SiP) module packaging from dc up to the K-band. The first transition provides better electromagnetic shielding, while the second one exhibits 40% wider bandwidth by including an air-cavity in the LTCC module. To specifically address board-level reliability, novel plastic-core solder balls as large as 1100 mum were employed. The measured 1-dB cutoff frequencies of the transition structures, all the way from the printed circuit board up to the top surface of the module package, were 19 and 27 GHz. In addition, equivalent circuit models for the transitions were developed.

Detection of Thermal Cycling-Induced Failures in RF/Microwave BGA Assemblies

The purpose of this paper was to investigate the effect of thermal cycling on the high-frequency behavior of ball grid array (BGA) interconnection structures. In order to characterize the applicability of RF measurements in predicting interconnection breakdown, a broadband BGA transition structure between a radio frequency printed wiring board (RF-PWB) and a ceramic module was fabricated. In addition to basic assemblies consisting of two BGA transitions between the module and substrate, the designed transition was applied in a passband filter module to demonstrate the effect of thermal cycling on the performance of a practical device, as well. The BGA test modules mounted on the PWBs were exposed to thermal cycling testing over a temperature range of -40degC to + 125degC. To detect interconnection failures induced by cyclic thermal stresses, both dc resistance and scattering parameter measurements were performed on the test assemblies at specific intervals. Parallel to the electrical measurements, crack propagation in the vicinity of the BGA transition structure was investigated using scanning acoustic microscopy (SAM). Moreover, scanning electron microscopy (SEM) was used to determine the failure mechanisms of the test assemblies. Degradation of the signal transmission characteristics of the basic assemblies was first observed at higher microwave frequencies as an increase in signal return loss (|S11|) and/or a change in its phase. The effect of TCT on the filter assembly was more constant and clearer to observe in the phase than in the magnitude of S11 in the passband. The dc resistance measurements showed no indication of degradation in any of the tested assemblies.

An Ultra-Wideband BGA-Via Transition for High-Speed Digital and Millimeter-Wave Packaging Applications

This paper presents a high-performance BGA-via transition structure suitable for multilayer system-in-package (SiP) applications over a wide frequency range from DC up to the F-band. The main issues involved in designing and optimizing the entire vertical transition path, starting from a motherboard and ending at the top surface of a BGA module package are outlined. The module substrates were manufactured in a standard, multilayer low-temperature co-fired ceramic (LTCC) process. The ceramic modules with plastic-core solder balls were mounted on a motherboard using standard surface-mount assembly processes. The RF performance of the developed transition structure was validated with on-wafer scattering parameter measurements. The measured results correlated very well with full-wave electromagnetic (EM) simulations, exhibiting return and insertion loss values better than 22 dB and 0.6 dB, respectively, up to 50 GHz. Moreover, the EM simulations demonstrated that the 1-dB cut-off frequency of the complete BGA-via transition structure can be extended from 55 GHz up to nearly 70 GHz at the expense of poorer return loss.

Ultra-Wideband Shielded Vertical Via Transitions from DC up to the V-Band

This paper presents three shielded vertical via transition designs applicable in millimeter-wave module packaging from DC up to the F-band. The optimized transition structures were fabricated using a standard low-temperature co-fired ceramic (LTCC) process. The measured scattering parameter results of the back-to-back via transition structures showed an exceptionally wide bandwidth with return losses better than 18 dB up to 50 GHz. The extracted insertion loss values of the single transitions were less than about 0.4 dB at 50 GHz. Moreover, full-wave electromagnetic (EM) simulations demonstrated the high potential of two of these via transitions up to 70 GHz

Low-Loss and Wideband Package Transitions for Microwave and Millimeter-Wave MCMs

This paper presents high-performance flip-chip, through-substrate via and board-level BGA transition designs applicable in microwave and millimeter-wave multichip module (MCM) assemblies. Full-wave electromagnetic analysis was performed to achieve optimized transition structures. Interconnection test structures were fabricated in ceramic substrates and their performance was validated using on-wafer scattering parameter measurements. Both the flip-chip transition and the through-substrate via transition with a height of 800 mum exhibited return losses better than 25 dB and 20 dB, respectively, with low transmission losses up to 50 GHz. Furthermore, the wideband board-level BGA transition with a standoff height of 500 showed low insertion loss (< 0.5 dB) over a wide frequency range, from direct current (dc) up to 32.5 GHz.

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...

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...

High performance vertical interconnections for millimeter-wave multichip modules

This paper presents high performance flip-chip and through-substrate via transition designs applicable in millimeter-wave single or multichip module assemblies. Full-wave electromagnetic analysis is performed to achieve an optimized transition topology. Interconnection test structures were fabricated in ceramic substrates and performance was successfully validated by on-wafer scattering parameter measurements up to 50 GHz. Both the flip-chip transition and the through-substrate via transition with a height of 800 /spl mu/m exhibited return loss better than 25 dB and 20 dB, respectively, with very low transmission losses within the entire measured band.

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...