Effect of Cu in Pb Free Solder Ball on the Microstructure of BGA Joints with Au/Ni Coated Cu Pads

Uenishi, Koji; Saeki, Toshio; Kohara, Yasuhiro; Kobayashi, Kojiro F.; Shoji, Ikuo; Nishiura, Masataka; Yamamoto, Masahiro

doi:10.2320/matertrans.42.756

Cited by 19 publications

(16 citation statements)

References 7 publications

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“…5,6) Specifically, Cu that dissolves from the core ball into the solder during reflow forms a Cu-Sn based reaction layer at the interface between the solder ball and pad. 7,8) Since most of this dissolved Cu was consumed to form the Cu-Sn reaction layer and little Cu is left in the solder ball, this Cu-Sn based reaction layer grows very little during thermal exposure at 423 K. Consequently, the joint strength using Cu core balls is only slightly degraded by thermal exposure at 423 K.…”

Section: Introductionmentioning

confidence: 99%

“…However, the growth rate of η -(Au, Cu) 6 Sn 5 formed solderNi plating became comparable with that of Ni 3 Sn 4 because Sn-Ag solder changes the reaction layer formed at the interface with Ni plating from Ni-Sn based compounds to an η phase. 7,8) For joints using Cu-core solder balls, Cu dissolved from the Cu-core ball during reflow affected the interaction with Ni plating. Similarly, an η -(Au, Cu) 6 Sn 5 reaction layer was formed on the boundary between the solder and the Cu most of the Cu in the solder ball was exhausted in forming the η reaction layer and hardly existed in the solder after reflow.…”

Section: Melting Behavior Of Solder Ballsmentioning

confidence: 99%

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Melting and Joining Behavior of Sn/Ag and Sn-Ag/Sn-Bi Plating on Cu Core Ball

et al. 2002

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We fabricated Cu core Sn-Ag solder balls by plating pure Sn and Ag on Cu balls and clarified that Sn/Ag plating began to melt at a rather low temperature, the eutectic temperature of Sn-Ag-Cu. This early melting at the eutectic temperature was ascribed to the diffusion of Cu and Ag into the Sn plating during the heating process. We investigated the solderability of the BGA joint with the Ni/Au coated Cu pad to compare it with that of the commercial Sn-Ag and Sn-Ag-Cu balls. After reflow soldering, we observed a eutectic microstructure composed of β-Sn, Ag 3 Sn, and Cu 6 Sn 5 phases in the solder, and a η -(Au, Cu, Ni) 6 Sn 5 reaction layer was formed at the interface between the solder and the Cu pad. The BGA joint using Cu core solder balls could prevent the degradation of joint strength during aging at 423 K because of the slower growth rate of the η -(Au, Cu, Ni) 6 Sn 5 reaction layer formed at the solder-pad interface. Furthermore, we were able to fabricate Cu-cored, multicomponent Sn-Ag-Bi balls by sequentially coating binary Sn-Ag and Sn-Bi solders onto Cu balls. The coated balls also exhibited almost the same melting and soldering behaviors as those of the previously alloyed Sn-2Ag-0.75Cu-3Bi solders.

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Section: Introductionmentioning

confidence: 99%

Section: Melting Behavior Of Solder Ballsmentioning

confidence: 99%

Melting and Joining Behavior of Sn/Ag and Sn-Ag/Sn-Bi Plating on Cu Core Ball

et al. 2002

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“…[2] Since the joints are formed with solder balls, many studies of the reliability of the joints made with lead-free solder balls have been performed. [3][4][5][6][7][8][9][10][11][12][13] In most of these studies, the joint strength of the solder ball joint was examined at lower shear speeds using a ball shear tool. Since the increasing popularity of mobile products has made the impact reliability of the solder ball joint a critical issue, [14] impact tests have been used to examine the impact strength of solder ball joints at higher shear speeds.…”

Section: Introductionmentioning

confidence: 99%

Effect of Shear Speed on the Ball Shear Strength of Sn-3Ag-0.5Cu Solder Ball Joints

Shohji

Shimoyama

Ishikawa

et al. 2008

Transactions of The Japan Institute of Electronics Packaging

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“…This is thought to occur because the (Cu,Ni) 6 Sn 5 layer acts as a barrier layer, suppressing the diffusion of Ni from the electroless Ni-P plating to the solder layer. 9) However, in the samples with 250 and 500 nm Au coating, a thin P-rich layer was observed at the interface. This indicates that even using the Sn-Ag-Cu solder, a thick Au coating (>250 nm) causes the formation of a P-rich layer on the interface after reflowsoldering.…”

Section: Methodsmentioning

confidence: 99%

Sn-Ag Based Solders Bonded to Ni-P/Au Plating: Effects of Interfacial Structure on Joint Strength

et al. 2003

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This study investigates interfacial reaction and joint strength of Sn-Ag and Sn-Ag-Cu solder balls bonded to electroless Ni-P plating with various thicknesses of Au coating (50, 250 and 500 nm). For the Sn-Ag solder joints, a P-rich layer formed after reflow-soldering at the joint interface, regardless of thickness of the Au coating. However, for the Sn-Ag-Cu solder joints, a P-rich layer formed at the joint interface only in those samples with Au coating of 250 and 500 nm. Fractures were found to occur at the interface, and the joint strength degraded at Au thickness of >250 nm for both the Sn-Ag and Sn-Ag-Cu solder joints. An Au thickness of 50 nm resulted in the best joint strength.

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Effect of Cu in Pb Free Solder Ball on the Microstructure of BGA Joints with Au/Ni Coated Cu Pads

Cited by 19 publications

References 7 publications

Melting and Joining Behavior of Sn/Ag and Sn-Ag/Sn-Bi Plating on Cu Core Ball

Melting and Joining Behavior of Sn/Ag and Sn-Ag/Sn-Bi Plating on Cu Core Ball

Effect of Shear Speed on the Ball Shear Strength of Sn-3Ag-0.5Cu Solder Ball Joints

Sn-Ag Based Solders Bonded to Ni-P/Au Plating: Effects of Interfacial Structure on Joint Strength

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