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Article
Publication date: 13 April 2010

Olli Nousiainen, Timo Urhonen, Tero Kangasvieri, Risto Rautioaho and Jouko Vähäkangas

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…

385

Abstract

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 fabricated and exposed to a TCT in a 0-100°C temperature range. The characteristic lifetime of the test assemblies was determined using DC resistance measurements. The failure mechanisms of the interconnections were verified using scanning acoustic microscopy, SEM and finite element (FE)-SEM investigations.

Findings

This work showed that the solderability of AgPt-metallized LTCC modules was poor, resulting in excessive voiding. This problem was avoided by using pre-tinned modules. In the test assemblies, the Sn4Ag0.5Cu joints had a lower void content and a higher characteristic lifetime compared with the Sn3Ag0.5Cu0.5In0.05Ni joints. Furthermore, it was observed that the Sn3Ag0.5Cu0.5In0.05Ni joints were more prone to fail along the interface between the Ag3Sn layer and the solder matrix than were the Sn4Ag0.5Cu joints. It was assumed that the observed difference in the primary failure mechanisms resulted in the decreased lifetime duration of the SnAgCu-InNi/Arlon in both temperature cycling conditions.

Originality/value

The results proved that the solderability of both solders in AgPt-metallized modules in a typical surface mount technology process was poor; however, the solderability of the test modules can be notably enhanced with pre-tinned pads. This work also demonstrated the effect of the metallization/solder pair on the failure mechanisms and failure rate in LTCC/PWB assemblies with LGA joints; the work also proved in the TCT, over a temperature range of 0-100°C, that using the present LGA joints in LTCC/PWB assemblies with a high global thermal mismatch did not increase the lifetime duration of the joints to the preferred level (3,000 cycles), whereas the performance of these joints was adequate in assemblies with a low global thermal mismatch. Moreover, the results indicated that using the LGA joint configuration enhanced the reliability of the LTCC/PWB assemblies compared with similar assemblies with collapsible ball grid array solder spheres.

Details

Soldering & Surface Mount Technology, vol. 22 no. 2
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 27 May 2014

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…

195

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.

Details

Soldering & Surface Mount Technology, vol. 26 no. 3
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 3 July 2007

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…

333

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

Soldering & Surface Mount Technology, vol. 19 no. 3
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 1 September 2005

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.

744

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.

Details

Soldering & Surface Mount Technology, vol. 17 no. 3
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 29 June 2010

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…

289

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.

Details

Soldering & Surface Mount Technology, vol. 22 no. 3
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 8 February 2011

O. Nousiainen, T. Kangasvieri, R. Rautioaho and J. Vähäkangas

The purpose of this paper is to investigate the thermal fatigue endurance of two lead‐free solders used in composite solder joints consisting of plastic core solder balls (PCSB…

439

Abstract

Purpose

The purpose of this paper is to investigate the thermal fatigue endurance of two lead‐free solders used in composite solder joints consisting of plastic core solder balls (PCSB) and different solder materials, in order to assess their feasibility in low‐temperature cofired ceramic (LTCC)/printed wiring board (PWB) assemblies.

Design/methodology/approach

The characteristic lifetime of these joints was determined in a thermal cycling test (TCT) over a temperature range of −40‐125°C. Their failure mechanisms were analyzed after the TCT using scanning acoustic and optical microscopy, scanning electronic microscope, and field emission scanning electronic microscope investigation.

Findings

The results showed that four different failure mechanisms existed in the test assemblies cracking in the mixed ceramic/metallization zone; or a mixed transgranular/intergranular failure occurred at the low temperature extreme; whereas an intergranular failure within the solder matrix; or separation of the intermetallic layer and the solder matrix occurred at the high temperature extreme. Sn3Ag0.5Cu0.5In0.05Ni was more resistant to mixed transgranular/intergranular failure, but had poor adhesion with the Ag3Sn layer. On the other hand, cracking in the mixed ceramic/metallization zone typically existed in the joints with Sn2.5Ag0.8Cu0.5Sb solder, whereas the joints with Sn3Ag0.5Cu0.5In0.05Ni were practically free of these cracks. The characteristic lifetimes of both test joint configurations were at the same level (800‐1,000) compared with joints consisted of Sn4Ag0.5Cu solder and PCSB studied earlier.

Originality/value

The study investigated in detail the failure mechanisms of the Sn3Ag0.5Cu0.5In0.05Ni and Sn2.5Ag0.8Cu0.5Sb solders under harsh accelerated test conditions. It was proved that these solders behaved similarly to the ternary SnAgCu solders in these conditions and no improvement can be achieved by utilizing these solders in the non‐collpasible solder joints of LTCC/PWB assemblies.

Details

Soldering & Surface Mount Technology, vol. 23 no. 1
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 12 April 2011

O. Nousiainen, O. Salmela, J. Putaala and T. Kangasvieri

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…

279

Abstract

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. Lifetime predictions of the test assemblies were calculated using the recalibrated Engelmaier model.

Findings

This work showed that indium alloying increased the characteristic lifetime of LGA joints by 15 percent compared with Sn3.8Ag0.7Cu joints. SEM/EDS analysis showed that alloying changed the composition, size, and distribution of intermetallic compounds within the solder matrix. It was also observed that a solid‐state phase transformation (Cu,Ni)6Sn5(→ (Ni,Cu)3Sn4 occurred at the Ni/(Cu,Ni)6Sn5 interface. Moreover, the results pointed out that individual recalibration curves for ceramic package/PWB assemblies with high (≥ 10 ppm/°C) and low (≈ 3‐4 ppm/°C) global thermal mismatches and different package thicknesses should be determined before the lifetime of LGA‐type assemblies can be predicted accurately using the recalibrated Engelmaier model.

Originality/value

The results proved that indium alloying of LGA joints can be done using In‐containing solder on pre‐tinned pads of an LTCC module, despite the different liquidus temperatures of the In‐containing and Sn3.8Ag0.7Cu solders. The characteristic metallurgical features and enhanced thermal fatigue endurance of the In‐alloyed SnAgCu joints were also determined. Finally, this work demonstrated the problems that exist in predicting the lifetime of ceramic packages with LGA joints using analytical modeling, and proposals for developing the recalibrated Engelmaier model to achieve more accurate results with different ceramic packages/PWB assemblies are given.

Details

Soldering & Surface Mount Technology, vol. 23 no. 2
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 27 June 2008

O. Nousiainen, T. Kangasvieri, R. Rautioaho and J. Vähäkangas

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…

452

Abstract

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 characteristic lifetimes of over 5,500 and 1,400 cycles, respectively, were achieved. Compared with Sn4Ag0.5Cu/plastic‐core solder balls (PCSB)/Sn4Ag0.5Cu joints, the characteristic lifetime of the SAC‐In/PCSB/SAC joints increased over 55 per cent in the harsh (−40 to 125°C) TCT conditions. In the milder test conditions (0 to 100°C), the characteristic lifetime of the SAC‐In/PCSB/SAC joints increased 30 per cent compared with the SAC/PCSB/SAC joints.

Originality/value

The results proved that the enhanced creep/fatigue properties of the solder matrix resulted in satisfactory lifetime durations in the present lead‐free composite solder joints and, consequently, different primary failure mechanisms on the LTCC side due to the use of indium alloyed solder. Thus, the present joint configuration is assumed to be a promising solution for the further design of a reliable second‐level solder interconnection in LTCC/PWB assemblies with a high‐global thermal mismatch.

Details

Soldering & Surface Mount Technology, vol. 20 no. 3
Type: Research Article
ISSN: 0954-0911

Keywords

Available. Content available
Article
Publication date: 1 August 2001

153

Abstract

Details

Microelectronics International, vol. 18 no. 2
Type: Research Article
ISSN: 1356-5362

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