Evaluation of two novel lead‐free surface finishes

Ludwig, Richard; Lee, Ning‐Cheng; Fan, Chonglun; Zhang, Yun

doi:10.1108/09540910210444683

Cited by 10 publications

(6 citation statements)

References 2 publications

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“…The former aggravates the problem by introducing dead corners in the microvia holes that are not filled with solder paste and that in turn prevent adequate solder wetting (Jo et al , 2002). The latter worsens the voiding because of the poor solder wetting characteristics (Huang and Lee, 1999; Ludwig et al , 2001). Since lead‐free soldering is a global trend in electronics manufacturing (Lee, 1999, 1996) and microvia technology is here to stay due to its indispensable role in miniaturization (Beelen‐Hendrikx and Verguld, 2000), the hope of minimizing voiding, among all materials options, resides in the possibility of finding lead‐free alloys which have a lower tendency of producing voids during soldering.…”

Section: Introductionmentioning

confidence: 99%

Effect of SnAgCu composition on soldering performance

Huang

Dasgupta

Lee

2005

Soldering &Amp; Surface Mount Technology

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PurposeTombstoning and voiding have been plaguing the surface mount assembly industry for decades. The recent global move toward lead‐free soldering and the extensive adoption of microvia technology further aggravate the problems. The present study investigates the impact of SnAgCu (SAC) alloy composition on these important issues.Design/methodology/approachIn this study, tombstoning and voiding at microvias are studied for a series of SAC lead‐free solders, with an attempt to identify a possible “composition window” for controlling these problems. Properties which may be related to these problems, such as alloy surface tension, alloy melting pattern, and solder wetting behaviour, were investigated in order to assess the critical characteristics required to control these problems.FindingsThe results indicate that the tombstoning of SAC alloys is greatly influenced by the solder composition. Both the wetting force and the wetting time at a temperature well above the melting point have no correlation with the tombstoning frequencies. Because the tombstoning is caused by imbalanced wetting forces, the results suggest that the tombstoning may be controlled by the wetting at the onset of the paste melting stage. A maximum tombstoning incidence was observed for the 95.5Sn3.5Ag1Cu alloy. The tombstoning rate decreased with increasing deviation in Ag content from this composition. A differential scanning calorimetry (DSC) study indicated that this was mainly due to the increasing presence of the pasty phase in the solders, which result in a slower wetting speed at the onset of solder paste melting stage. Surface tension plays a minor role, with lower surface tension correlating with a higher tombstoning rate. The voiding rate at the microvias was studied by employing simulated microvias. The voiding level was lowest for the 95.5Sn3.8Ag0.7Cu and 95.5Sn3.5Ag1Cu alloys, and increases with a further decrease in the Ag content. The results indicate that voiding at microvias is governed by the via filling and the exclusion of fluxes. The voiding rate decreased with decreasing surface tension and increasing wetting force, which in turn is dictated by the solder wetting or spreading. Both low surface tension and high solder wetting prevents the flux from being entrapped within a microvia. A fast wetting speed may also facilitate reducing voiding. However, this factor is considered not as important as the final solder coverage area.Research limitations/implicationsIn general, compositions which deviate from the ternary eutectic SAC in Ag content, particularly with a Ag content lower than 3.5Ag, exhibit a greater solid fraction at the onset of melting, resulting in a lower tombstoning rate, presumably due to a slower wetting speed. The SAC compositions with an Ag content lower than 3.5 per cent, such as 2.5Ag, resulted in a lower tombstoning rate with minimal risk of forming Ag3Sn intermetallic platelets. On the other hand, ternary eutectic SAC exhibits a lower surface tension resulting in an easier solder spread or solder wetting...

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Section: Introductionmentioning

confidence: 99%

Effect of SnAgCu composition on soldering performance

Huang

Dasgupta

Lee

2005

Soldering &Amp; Surface Mount Technology

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“…The effect of the PCB on solder joints has been studied extensively in some respects, while many areas have been studied in less depth. For instance, the wetting characteristics of different PCB surface finishes have been widely studied, and it is commonly known that in most cases the solder paste wetting characteristics are better on immersion gold over electroless nickel (NiAu) than on an organic solderability preservative (OSP) (Sattiraju et al, 2002;Ludwig et al, 2002;Chung et al, 2002). Even though the wetting characteristics have been thoroughly studied, the effects of PCB surface finishes and structures on other issues, such as voids and the solder joint composition and structure have been less studied.…”

Section: Introductionmentioning

confidence: 99%

The effect of PCB surface finish on lead‐free solder joints

Nurmi

Sundelin²,

Ristolainen³

et al. 2005

Soldering &Amp; Surface Mount Technology

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Purpose -To study the behaviour of voids in PBGA solder joints and their influence on the lifetime of lead-free solder joints. Design/methodology/approach -The behaviour of voids was studied using micro via and land pad PWBs, PBGA components, and by measuring voids in the solder joints. The lifetimes of solder joints were tested using accelerated temperature tests. Findings -Number of factors affecting the solder joint lifetimes were found. The voids were discovered to have a significantly large influence on the solder joints. Practical implications -The findings can be used to achieve better soldering results, methods, and designs. Originality/value -In this paper, the effect and the behaviour of voids were studied profoundly. The findings can be valuable to researchers and process personnel.

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“…For instance, the wettability of finishes with lead-free solder alloys was widely investigated [3][4][5]. During soldering, interfacial reactions occur and intermetallic compounds (IMCs) form at the interfaces.…”

Section: Introductionmentioning

confidence: 99%