Olli Nousiainen

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.

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.

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...

Failure Detection of BGA Transition Structures at High Frequencies

The purpose of this paper was to investigate the effect of thermal cycling on the high frequency behavior of a BGA transition structure. A broadband microwave BGA transition structure between a RF-PWB and a ceramic module was designed and fabricated. The stand-off height of the composite BGA solder joints was 500 mum. The BGA test modules mounted on the PWBs were exposed to thermal cycling testing over a temperature range of -40...+125 degC. To detect interconnection failures induced by cyclic thermal stresses, both DC resistance and scattering parameter measurements (45 MHz-25 GHz) 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 in the signal transmission characteristics was first observed at higher microwave frequencies as an increase in signal return loss (|S11|). As the thermal cycling test proceeded, the reflected signal loss became more significant and gradually became pronounced at lower microwave frequencies. Pure DC resistance measurements showed no indication on the degradation of the transition structure

Enhanced thermal fatigue endurance and lifetime prediction of lead‐free LGA joints in LTCC modules

Purpose – The purpose of this paper is to describe the effect of indium alloying on the thermal fatigue endurance of Sn3.8Ag0.7Cu solder in low‐temperature co‐fired ceramic (LTCC) modules with land grid array (LGA) joints and the feasibility of using a recalibrated Engelmaier model to predict the lifetime of LGA joints as determined with a test assembly.Design/methodology/approach – Test assemblies were fabricated and exposed to a temperature cycling test over a temperature range of −40‐125°C. Organic printed wiring board (PWB) material with a low coefficient of thermal expansion was used to reduce the global thermal mismatch of the assembly. The characteristic lifetime, θ, of the test assemblies was determined using direct current resistance measurements. The metallurgy and failure mechanisms of the interconnections were verified using scanning acoustic microscopy, an optical microscope with polarized light, and scanning electron microscopy/energy dispersive spectrometry (SEM/EDS) investigations. Lifetim...

Lifetime Prediction of Non-Collapsible Solder Joints in LTCC/PWB Assemblies Using a Recalibrated Engelmaier's Model

The thermal fatigue endurances of lead-free (φ 500 and 1100 μm) plastic core solder ball (PCSB) ball grid array interconnections were investigated. The test assemblies were exposed to thermal cycling testing in temperature ranges of 0-100°C and -40 to +125°C. In addition, optical microscopy and scanning electron microscopy were used to characterize the interconnections. The characteristic lifetime data from this and earlier studies were contrasted with a recalibrated Engelmaiers model. After adjusting the model, feasibility was determined through test results of a partial array representing a real-use case. On the basis of this paper it was found that the recalibrated Engelmaiers model is, after adjustment, a suitable model for predicting the lifetime of PCSB assemblies.

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...

Effect of ENIG deposition on the failure mechanisms of thermomechanically loaded lead‐free 2nd level interconnections in LTCC/PWB assemblies

Purpose – The purpose of this paper is to investigate the effect of electroless NiAu (ENIG) deposition on the failure mechanisms and characteristic lifetimes of three different non‐collapsible lead‐free 2nd level interconnections in low‐temperature co‐fired ceramic (LTCC)/printed wiring board (PWB) assemblies.Design/methodology/approach – Five LTCC module/PWB assemblies were fabricated and exposed to a temperature cycling test over a −40 to 125°C temperature range. The characteristic lifetimes of these assemblies were determined using direct current resistance measurements. The failure mechanisms of the test assemblies were verified using X‐ray and scanning acoustic microscopy, optical microscopy with polarized light, scanning electron microscope (SEM)/energy dispersive spectroscopy and field emission‐SEM investigation.Findings – A stable intermetallic compound (IMC) layer is formed between the Ni deposit and solder matrix during reflow soldering. The layer thickness does not grow excessively and the inte...

Lifetime prediction and design aspects of reliable lead-free non-collapsible BGA joints in LTCC packages for RF/microwave telecommunication applications

Purpose – The purpose of this paper is to describe the behavior of different lead-free solders (95.5Sn3.8Ag0.7Cu, i.e. SAC387 and Sn7In4.1Ag0.5Cu, i.e. SAC-In) in thermomechanically loaded non-collapsible ball grid array (BGA) joints of a low-temperature co-fired ceramic (LTCC) module. The validity of a modified Engelmaier’s model was tested to verify its capability to predict the characteristic lifetime of an LTCC module assembly implementable in field applications. Design/methodology/approach – Five printed wiring board (PWB) assemblies, each carrying eight LTCC modules, were fabricated and exposed to a temperature cycling test over a −40 to 125°C temperature range to determine the characteristic lifetimes of interconnections in the LTCC module/PWB assemblies. The failure mechanisms of the test assemblies were verified using scanning acoustic microscopy, scanning electron microscopy (SEM) and field emission SEM investigation. A stress-dependent Engelmaier’s model, adjusted for plastic-core solder ball (...