Search results

1 – 10 of over 2000
Article
Publication date: 1 February 1988

L.‐G. Liljestrand and L.‐O. Andersson

Telecom equipment is subject to thermal cycles caused by both variations in temperature between day and night and variations in the telephone traffic. To simulate such thermal

Abstract

Telecom equipment is subject to thermal cycles caused by both variations in temperature between day and night and variations in the telephone traffic. To simulate such thermal excursions, accelerated thermal cycle testing between — 10°C and 100°C has been established as a standard method within Ericsson Telecom. Thermal cycle tests have been carried out for frequencies ranging from one cycle per day to 30 cycles per hour in order to cover the different thermal excursions that occur in telecom equipment. It has been found that the life of a surface mounted PWB assembly can be predicted from the accelerated testing results using a frequency modified Coffin‐Manson relation. Factors which influence the fatigue life of solder joints such as solder material, compliant leads, compliant surface layers and mismatch between package and board are discussed. Based on results from accelerated testing it is suggested that the optimal PWB design for leadless ceramic chip carriers should be a moderate TCE matching combined with a compliant surface layer.

Details

Circuit World, vol. 14 no. 3
Type: Research Article
ISSN: 0305-6120

Article
Publication date: 1 March 1989

J.W. Morris, D. Grivas, D. Tribula, T. Summers and D. Frear

This paper discusses the microstructures of solder joints and the mechanism of thermal fatigue, which is an important source of failure in electronic devices. The solder joints…

43

Abstract

This paper discusses the microstructures of solder joints and the mechanism of thermal fatigue, which is an important source of failure in electronic devices. The solder joints studied were near‐eutectic Pb‐Sn solder contacts on copper. The microstructure of the joints is described. While the fatigue life of near‐eutectic solder joints is strongly dependent on the operating conditions and on the microstructure of the joint, the metallurgical mechanisms of failure are surprisingly constant. When the cyclic load is in shear at temperatures above room temperature the shear strain is inhomogeneous, and induces a rapid coarsening of the eutectic microstructure that concentrates the deformation in well‐defined bands parallel to the joint interface. Fatigue cracks propagate along the Sn‐Sn grain boundaries and join across the Pb‐rich regions to cause ultimate failure. The failure occurs through the bulk solder unless the joint is so thin that the intermetallic layer at the interface is a significant fraction of the joint thickness, in which case failure may be accelerated by cracking through the intermetallic layer. The coarsening and subsequent failure are influenced more strongly by the number of thermal cycles than by the time of exposure to high temperature, at least for hold times up to one hour. Thermal fatigue in tension does not cause well‐defined coarsened bands, but often leads to rapid failure through cracking of the brittle intermetallic layer. Implications are drawn for the design of accelerated fatigue tests and the development of new solders with exceptional fatigue resistance.

Details

Soldering & Surface Mount Technology, vol. 1 no. 3
Type: Research Article
ISSN: 0954-0911

Article
Publication date: 1 February 1985

W. Engelmaier

One concern that has slowed the progress of surface mounted technology, in particular leadless chip carriers, has been the question of the reliability of the surface mount…

Abstract

One concern that has slowed the progress of surface mounted technology, in particular leadless chip carriers, has been the question of the reliability of the surface mount attachment technology. This concern follows from the realisation that the functional reliability of surface mount technology is a very complex issue involving many not very well understood components. What is needed is a relatively simple, useful, predictive model. The model reported here sidesteps the numerous complex underlying issues, which, if considered separately, make a predictive reliability model all but impossible, by taking a purely phenomenological approach and relegating second‐order effects to a lumped empirical figure of merit.

Details

Circuit World, vol. 11 no. 3
Type: Research Article
ISSN: 0305-6120

Article
Publication date: 1 March 1968

N.F. Harpur

DEVELOPMENT of the supersonic transport is involving a wide variety of activities in all fields of aeronautics. This paper describes the work which has taken place, or is planned…

Abstract

DEVELOPMENT of the supersonic transport is involving a wide variety of activities in all fields of aeronautics. This paper describes the work which has taken place, or is planned, in the field of structures. Although Concorde is designed for Much 2, a speed at which aluminium alloys can continue to be used as the primary structural materials, evaluation of the particular alloys chosen and study of their behaviour under complex temperature‐stress histories involves considerable laboratory effort. While many aircraft have already operated under these conditions none has previously had to last for at least 45,000 hours in service. This gives rise to the two most significant new design considerations, viz. creep and thermal fatigue. Creep affects the choice of basic material, the design of joints and the design of structures through its interaction with fatigue life. Thermal stresses, arising from differential expansions within the structure and superimposed upon the normal flight stresses, have a more important effect on fatigue design than on static strength. While the experimental techniques involved are novel, practical methods of accelerated thermal testing using convective heating and cooling are described.

Details

Aircraft Engineering and Aerospace Technology, vol. 40 no. 3
Type: Research Article
ISSN: 0002-2667

Article
Publication date: 1 March 1992

J. Glazer, P.A. Kramer and J.W. Morris

The effect of gold (Au) on the reliability of 0.65 mm pitch surface mount solder joints between plastic quad flat packs and Cu‐Ni‐Au FR‐4 printed circuit boards was investigated…

Abstract

The effect of gold (Au) on the reliability of 0.65 mm pitch surface mount solder joints between plastic quad flat packs and Cu‐Ni‐Au FR‐4 printed circuit boards was investigated. Cu‐Ni‐Au is a desirable printed circuit board finish for multi‐chip modules or printed circuit boards that would otherwise require a selective Au finish, for example for edge connectors or wire bondable parts. However, Au is known to embrittle solder when it is present in sufficiently high concentrations, creating a concern that solder joint fatigue life in service will also be adversely affected. This paper reports the results of mechanical shock, mechanical vibration and thermal cycling testing of fine pitch solder joints containing varying amounts of Au. Tests were performed on as‐soldered joints and on joints that had been heat‐treated to evolve the microstructure towards equilibrium. The tests were designed to accelerate in‐service conditions in a typical industrial environment. Under these conditions, the Au concentrations tested did not promote solder joint failures. Microstructural characterisation of the distribution and morphology of the Au‐, Ni‐ and Cu‐Sn intermetallics in the joint before and after accelerated testing was also performed. On the basis of these observations it is recommended that the Au concentration in solder joints between plastic quad flat packs and Cu‐Ni‐Au FR‐4 printed circuit boards not exceed 3.0 wt.%.

Details

Circuit World, vol. 18 no. 4
Type: Research Article
ISSN: 0305-6120

Article
Publication date: 13 April 2010

Guangcheng Dong, Xu Chen, Xinjian Zhang, Khai D.T. Ngo and Guo-Quan Lu

The purpose of this paper is to study the phenomenology of Al2O3-DBC substrate thermal-cracking under different high temperature cyclic loadings. The extremely low cycle fatigue

Abstract

Purpose

The purpose of this paper is to study the phenomenology of Al2O3-DBC substrate thermal-cracking under different high temperature cyclic loadings. The extremely low cycle fatigue (ELCF) life prediction model for ductile materials was used to describe the thermal fatigue life of Al2O3-DBC substrates.

Design/methodology/approach

Four groups of thermal cycling tests using Al2O3-DBC substrates with 0.65 mm thick copper were conducted using different peak temperatures. The failure samples were observed by optical microscope. The thermal plastic strain distribution in the Al2O3-DBC substrates was analyzed using a finite element method with the Chaboche model for describing plastic deformation of copper. The ELCF life prediction model was used to predict the life of Al2O3-DBC substrates under high temperature cyclic loadings.

Findings

Interface cracking was observed to initiate at the short edge of the bonded copper and deviated into the ceramic layer when the crack grew beyond the critical length of 0.1-0.8 mm. The interface crack deviated into the ceramic layer at different thickness and grew parallel to the interface layer between the ceramic layer and copper layer. The crack propagation stopped after certain cycles. The copper layer with 10-20 μm thick alumina inside was not split away totally from the ceramic layer. The ELCF life prediction model could predict the life of Al2O3-DBC substrates well under high temperature cyclic loading. The material constants in the extremely low fatigue life prediction model were obtained using thermal fatigue tests results.

Research limitations/implications

The influence of copper layer thickness and ceramic layer thickness on thermal cracking characteristics of DBC substrate should be studied in the future. Failure models should also be further investigated.

Originality/value

The failure model of Al2O3-DBC substrates under high temperature cyclic loading was studied. A method for predicting the life of the substrate samples under high temperature cyclic loading was proposed.

Details

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

Keywords

Article
Publication date: 1 February 1990

C. Lea

The loss of reliability of a PTH soldered joint caused by unnecessary re‐working after wave soldering is considered. Standardised joints are re‐worked under conditions that…

Abstract

The loss of reliability of a PTH soldered joint caused by unnecessary re‐working after wave soldering is considered. Standardised joints are re‐worked under conditions that closely control the temperature of the soldering iron tip, the time of contact of the tip to the joint, the angle and the contact pressure of the soldering iron, the amount of flux and the amount of extra solder applied. The service life of the joints is assessed using accelerated thermal cycling between ‐20°C and +100°C. In all cases, the service life of these test joints is degraded by re‐working. The effect becomes worse when the temperature and time of re‐work are increased. The degradation of fatigue performance is associated with changes in the solder fillet microstructure. The effects on fatigue performance of changing the fillet size by adding extra solder during re‐work are complex, but explainable in general terms. The results obtained from the controlled laboratory rework tests are corroborated by test assemblies re‐worked to companies' in‐house workmanship standards and by field data.

Details

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

Article
Publication date: 1 April 2003

Daniel T. Rooney, N. Todd Castello, Mike Cibulsky, Doug Abbott and Dongji Xie

The mechanical integrity of solder joint interconnects in PWB assemblies with micro ‐ BGA, chip scale, and LGA packages are being questioned as the size and pitch decrease…

Abstract

The mechanical integrity of solder joint interconnects in PWB assemblies with micro ‐ BGA, chip scale, and LGA packages are being questioned as the size and pitch decrease. Three‐point cyclic bend testing provides a useful tool for characterizing the expected mechanical cycling fatigue reliability of PWB assemblies. Cyclic bend testing is useful for characterizing bending issues in electronic assemblies such as repetitive keypad actuation in cell phone products. This paper presents the results of three‐point bend testing of PWB assemblies with fine pitch packages. The methodology of materials analyses of the metallurgy of solder interconnects following mechanical bending and thermal cycle testing is described.

Details

Microelectronics International, vol. 20 no. 1
Type: Research Article
ISSN: 1356-5362

Keywords

Article
Publication date: 1 March 1990

C. Lea

One family of defects in soldered electronic assemblies that is almost invariably re‐worked is that due to outgassing, manifested as visible blowholes and solder blow‐out. It is…

Abstract

One family of defects in soldered electronic assemblies that is almost invariably re‐worked is that due to outgassing, manifested as visible blowholes and solder blow‐out. It is known that re‐working can be very detrimental to the service life of an electronic assembly and should be avoided whenever possible. This paper describes work aimed to determine whether outgassing faults such as blowholes are harmful to service performance or whether more harm will be done by re‐working such faults. Standard test plated‐through‐hole (PTH) assemblies with controlled degrees of outgassing faults have been subjected to mechanical testing, thermal shock testing, mechanical fatigue, low cycle thermal fatigue and corrosion testing. Measurements in all these régimes have been carried out quantitatively with baseline controls. No evidence of significant loss of solder joint performance has been found, even for severe cases of solder loss. On the contrary, in cyclic fatigue testing, solder fillets with outgassing faults exhibit statistically significant performance enhancement. The conspicuous nature of blowholing and solder blow‐out undoubtedly over‐emphasises the problem during visual quality control inspection. Provided the copper barrel has been wet by the solder, outgassing faults should not be re‐worked. These faults should be used as process indicators and to draw attention to processes and the need for process control.

Details

Circuit World, vol. 16 no. 4
Type: Research Article
ISSN: 0305-6120

Article
Publication date: 7 April 2015

Jibing Chen, Yanfang Yin, Jianping Ye and Yiping Wu

The purpose of this paper is to investigate the thermal fatigue behavior of a single Sn-3.0Ag-0.5Cu (SAC) lead-free and 63Sn-37Pb (SnPb) solder joint treated by rapidly…

Abstract

Purpose

The purpose of this paper is to investigate the thermal fatigue behavior of a single Sn-3.0Ag-0.5Cu (SAC) lead-free and 63Sn-37Pb (SnPb) solder joint treated by rapidly alternating heating and cooling cycles.

Design/methodology/approach

With the application of electromagnetic-induced heating, the specimen was heated and cooled, controlled with a system that uses a fuzzy logic algorithm. The microstructure and morphology of the interface between the solder ball and Cu substrate was observed using scanning electron microscopy. The intermetallic compounds and the solder bump surface were analyzed by energy-dispersive X-ray spectroscopy and X-ray diffraction, respectively.

Findings

The experimental results showed that rapid thermal cycling had an evident influence on the surface and interfacial microstructure of a single solder joint. The experiment revealed that microcracks originate and propagate on the superficial oxide of the solder bump after rapid thermal cycling.

Originality/value

Analysis, based on finite element modeling and metal thermal fatigue mechanism, determined that the rimous cracks can be explained by the heat deformation theory and the function of temperature distribution in materials physics.

Details

Soldering & Surface Mount Technology, vol. 27 no. 2
Type: Research Article
ISSN: 0954-0911

Keywords

1 – 10 of over 2000