Effect of Gold on the Reliability of Fine Pitch Surface Mount Solder Joints

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

doi:10.1108/eb046177

Cited by 25 publications

(11 citation statements)

References 3 publications

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“…The volume of the deposited solder is the key parameter as it affects the mechanical and dimensional characteristics of the solder joint and, ultimately, the reliability of the assembly. This is particularly true when gold is used as surface finish [5][6][7][8][9] because a gold concentration of 5 wt.% or lower causes embrittlement [10].…”

Section: Solder Joint Designmentioning

confidence: 99%

Gold in Flux-less Bonding: Noble or not Noble

et al. 2011

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This work highlights the solder joints reliability issues emerged during the development of a novel compliant contacting technology. The peculiar process in this technology is a mechanical lifting procedure in which a pulling force is exerted onto 63Sn-37Pb (eutectic) solder joints (realized by a flux-less thermo compression process), releasing metal traces from the substrate, to form free standing vertical structures. Since joints mechanical characteristics are critical for the successful fabrication of contacts, different bonding conditions (inert or forming atmosphere, temperature rates) and surface finishing (electroplated gold and preformed solder) have been tested. SEM and EDX analyses have been performed on failing joints to investigate failure causes and classify defect typologies. A constantly higher failure rate (percent number of failing joints) has been observed on gold finished surfaces. Analyses proved that such unusual rate was due to contamination of gold surface left by additives in the plating bath and to the embrittlement caused by gold diffusion into molten solder. Plating additives contamination reduces the wettability of gold surfaces. Concentration values of 3 wt.% for gold, considered safe for surface mount applications, caused embrittlement in solder bumps of 20-40 μm diameters.

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Section: Solder Joint Designmentioning

confidence: 99%

Gold in Flux-less Bonding: Noble or not Noble

et al. 2011

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“…To prevent this from occurring, the thickness of the gold layer has to be limited to approximately 380 nm. [11] …”

Section: Soldermentioning

confidence: 99%

Parallel Packaging of Micro Electro Mechanical Systems (MEMS) Using Self-alignment

Taprogge

Beyeler²,

Steinecker

et al. 2012

Precision Assembly Technologies and Systems

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Abstract. Packaging is one of the major cost drivers for MEMS devices. Currently wire bonding is the dominant method for electrically connecting MEMS chips to substrate. Using self-alignment a method for packaging multiple MEMS at the same time has been developed. The presented process achieves high throughput and precise alignment at low cost. The Controlled Collapse Re-flow Chip Joining (C-4) process has been adapted to the specific requirements of MEMS. The combination of coarse robotics and liquid solder self-alignment guarantees precise positioning and alignment of the individual MEMS chips to the respective substrates. The new method has been implemented in a case study. In the study force sensors have been packaged. Precise angular alignment of the sensors is critical for receiving accurate measurements. Results of the case study are presented.

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“…This phase is formed by the high dissolution rate of Cu into the liquid solder and the high solubility of Cu in ζ-phase due to the nature of between Au and Cu as discussed in chapter 2. should be limited in order to avoid the deleterious effect on the joint reliability that a large amount of AuSn 4 intermetallics within the bulk can have. [3][4][5] In the case of eutectic Au-Sn solder, the precipitation of AuSn 4 is not a concern since it does not occur. However, the amount of Au dissolved into eutectic Au-Sn should be still carefully controlled since it modifies the nominal eutectic composition and thereby the microstructure as shown in Figure 3.2(a).…”

Section: Bulk Solder Of the Bumpmentioning

confidence: 99%

“…Among other concerns, the AuSn 4 phase is known to embrittle the eutectic Pb-Sn solder joint. [3][4][5]. Small alterations in solder composition due to reactions at the interface can significantly modify the microstructure of the solder joint and lead to significant effects on its mechanical behavior.…”

Section: Differences Between Solder Joints and Bulk Soldersmentioning

confidence: 99%

Microstructural evolution of eutectic Au-Sn solder joints

Song

2002

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Current trends toward miniaturization and the use of lead(Pb)-free solders in electronic packaging present new problems in the reliability of solder joints. This study was performed in order to understand the microstructure and microstructural evolution of small volumes of nominally eutectic Au-Sn solder joints (80Au-20Sn by weight), which gives insight into properties and reliability. The study particularly concentrated on the effects that the joint size and the type of substrate metallization have on both the bulk and interface microstructures of the joints. The systems studied were eutectic Au-Sn on Cu and Cu/electroless Ni/Au and for each system, two sets of sample geometries were used. The solubility characteristics and diffusional behavior of substrate metals into eutectic Au-Sn solder determines the detailed microstructure and microstructural evolution of the ultrafine eutectic Au-Sn joints. Two important things to be noted from the results are as follows: First, the overall microstructures of these joints are very coarse with respect to the size of joint, and hence the properties of the joints cannot be assumed from bulk solder data. Second, despite having a nominally similar starting eutectic Au-Sn composition, the microstructural features of the joints are unique for a given substrate metallization. Both of these results should be take into consideration during the design of reliable eutectic Au-Sn solder joints.

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Effect of Gold on the Reliability of Fine Pitch Surface Mount Solder Joints

Cited by 25 publications

References 3 publications

Gold in Flux-less Bonding: Noble or not Noble

Gold in Flux-less Bonding: Noble or not Noble

Parallel Packaging of Micro Electro Mechanical Systems (MEMS) Using Self-alignment

Microstructural evolution of eutectic Au-Sn solder joints

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