George MacMahon has been appointed Product Manager for Thick Film Materials by W. C. Heraeus, Hanau, Germany, to further increase the company's business throughout Europe and…
Abstract
George MacMahon has been appointed Product Manager for Thick Film Materials by W. C. Heraeus, Hanau, Germany, to further increase the company's business throughout Europe and beyond. He will help to co‐ordinate technical support for the general sales effort, including the presentation of technical information at meetings and exhibitions.
Morton International Inc. have purchased Hoechst AG's printed circuit materials business including their Ozatec dry film and liquid primary imaging photoresists, Ozatec liquid…
Abstract
Morton International Inc. have purchased Hoechst AG's printed circuit materials business including their Ozatec dry film and liquid primary imaging photoresists, Ozatec liquid photoimageable solder masks and related process equipment. Concurrently, Hoechst and its US subsidiary Hoechst Celanese Corporation purchased Morton's semiconductor photoresist business. Completion of these transactions was effective from 4 August 1993.
Olli Nousiaianen, Risto Rautioaho, Kari Kautio, Jussi Jääskeläinen and Seppo Leppävuori
To investigate the effect of the metallization and solder mask materials on the solder joint reliability of low temperature co‐fired ceramic (LTCC) modules.
Abstract
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 the −40‐125°C temperature range. The primary failure mechanism was solder joint cracking, whereas the AgPd‐metallized modules suffered from cracking in the ceramic. In the milder test conditions AgPd‐metallized modules showed better fatigue endurance than AgPt‐metallized modules.
Originality/value
This paper proves that the cracking in ceramic in the harsh test condition can be eliminated almost completely by using AgPt metallization instead of AgPd metallization in the present test module structure.
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O. Nousiainen, T. Kangasvieri, K. Kautio, R. Rautioaho and J. Vähäkangas
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…
Abstract
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 interface between the layer and solder is practically free from Kirkendall voids after the thermal cycling test (TCT) over a temperature range of −40 to 125°C. The adhesion between the IMC layer and solder matrix is sufficient to prevent separation of this interface, resulting in intergranular (creep) or mixed transgranular/intergranular (fatigue/creep) failure within the solder matrix. However, the thermal fatigue endurance of the lead‐free solder has a major effect on the characteristic lifetime, not the deposit material of the solder land. Depending on the thickness of the LTCC substrate and the composition of the lead‐free solder alloy, characteristic lifetimes of over 2,000 cycles are achieved in the TCT.
Originality/value
The paper investigates in detail the advantages and disadvantages of ENIG deposition in LTCC/PWB assemblies with a large global thermal mismatch (ΔCTE≥10 ppm/°C), considering the design and manufacturing stages of the solder joint configuration and its performance under harsh accelerated test conditions.
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Jussi Putaala, Olli Salmela, Olli Nousiainen, Tero Kangasvieri, Jouko Vähäkangas, Antti Uusimäki and Jyrki Lappalainen
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…
Abstract
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 (PCSB) BGA structures, was used to predict the characteristic lifetimes of the assemblies.
Findings
Depending on the joint configuration, characteristic lifetimes of up to 1,920 cycles were achieved in the thermal cycling testing. The results showed that intergranular (creep) failures occurred primarily only in the joints containing Sn7In4.1Ag0.5Cu solder. Other primary failure mechanisms (mixed transgranular/intergranular, separation of the intermetallic compound/solder interface and cracking in the interface between the ceramic and metallization) were observed in the other joint configurations. The modified Engelmaier’s model was found to predict the lifetime of interconnections with good accuracy. The results confirmed the superiority of SAC-In solder over SAC in terms of reliability, and also proved that an air cavity structure of the module, which enhances its radio frequency (RF) performance, did not degrade the reliability of the second-level interconnections of the test assemblies.
Originality/value
This paper shows the superiority of SAC-In solder over SAC387 solder in terms of reliability and verifies the applicability of the modified Engelmaier’s model as an accurate lifetime prediction method for PCSB BGA structures for the presented LTCC packages for RF/microwave telecommunication applications.
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Daniel Jean, W. Jack Lackey and Chad E. Duty
To describe the thermal imaging control system used to deposit lines of graphite in a laser chemical vapor deposition (LCVD) system.
Abstract
Purpose
To describe the thermal imaging control system used to deposit lines of graphite in a laser chemical vapor deposition (LCVD) system.
Design/methodology/approach
A thermal imaging‐based control system is applied to the LCVD process to deposit layered carbon lines of uniform height and width. A 100 W CO2 laser focused to a 200 μm diameter spot size is used to provide the heat source for the carbon deposition. A high resolution thermal imaging camera is used to monitor and control the average deposition temperature.
Findings
Carbon lines are grown with heights of 250 μm and widths of 170 μm consisting of 20 layers. Laser spot temperatures are in excess of 2,170°C, and the total pressure used is 1 atm with a 75 percent methane concentration and the remainder hydrogen. The length of the lines is 3.3 mm, and the scan speed is 5 mm/min. The volumetric deposition rate is 0.648 mm3/h.
Research limitations/implications
The temperature process control resulted in uniform geometry at the center of the lines, but it was not as effective at the ends of the lines where the geometry was more complex.
Originality/value
Introduces a control technique for uniform line deposition for the LCVD process, which represents a core building block for complex geometries. The establishment of basic control algorithms will enable LCVD to realize the potential for rapid prototyping of metals and ceramics with sub‐millimeter feature sizes.
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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.
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Modern semiconductor technologies have advanced to the level of sophistication where the benefits of the high functional and power density,high speed, low defect rate and low…
Abstract
Modern semiconductor technologies have advanced to the level of sophistication where the benefits of the high functional and power density, high speed, low defect rate and low wafer processing cost can seldom be fully utilised at the final equipment or even at the single packaged semiconductor component level due to the limitations of wire bonds and lead frame fan‐outs. This paper suggests a new assembly method where low‐cost contact bumps are deposited on semiconductor wafers and then the dice are reflow soldered or gang bonded to the substrate. The bumps are electroless nickel deposited and coated with a protective layer of gold. As the nickel bumps are non‐collapsible, they are better suited to Extra High Density Interconnections (EHDI) than the more usual solder bumps. The amount of solder must be accurately dispensed either on the die bumps or on the substrate bonding pads using various methods. Essential to the high volume assembly is fast pick‐and‐place operation and simultaneous soldering of all components in a reflow furnace. In certain applications bonding of the bumped device (one die at a time) can be done using reflow or thermocompression gang bonding by applying a heated thermode to the backside of the die. In this case, the bonding energy will be transferred through the die to the bumps. Tentative solder joint strength and reliability aspects are discussed. Further process and design improvements are suggested.
Details
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This study aims to investigate the day-of-the-week (DoW) effect in globally listed private equity (LPE) markets using daily data covering the period 2004–2021.
Abstract
Purpose
This study aims to investigate the day-of-the-week (DoW) effect in globally listed private equity (LPE) markets using daily data covering the period 2004–2021.
Design/methodology/approach
To investigate the existence of the DoW effect in globally LPE markets, ordinary least squares regression, generalised autoregressive conditional heteroscedasticity (GARCH) regression and robust regressions are used. In addition, robustness audits are conducted by subdividing the sampling period into two sub-periods: pre-financial and post-financial crisis.
Findings
Limited statistically significant evidence is found for the DoW effect. By taking time-varying volatility into account, a statistically significant DoW effect can be observed, indicating that the DoW effect is driven by time-varying volatility. Economic significance is captured through visual inspection of average daily returns, which illustrate that Monday returns are lower than the other weekdays.
Practical implications
The results have important implications on whether to adopt a DoW strategy for investors in LPE. The findings show that higher returns on selected days of the week for certain indices are possible.
Originality/value
To the best of the author’s knowledge, this paper provides the first study to examine the DoW effect for globally LPE markets by using LPX indices and contributes valuable insights on this growing asset class.