| Summary: | 碩士 === 義守大學 === 材料科學與工程學系碩士班 === 95 === This research paper includes surface finish of BGA (Ball Grid Array) solder pads and the lead-free solder ball combine with solder joints uses in electronic package technology. Nowadays, BGA metal surface finish, is produced to regard electroplating the way as mostly to deal with electroplate nickel and electricity gold-plated methods. But, in the electron industry, under the thin, short, & small demand, it wastes the design space and reduces the electron industry demand for fine pitch when BGA needs to draw the conductive line circuit to do plating with Nickel and Gold.
Consequently, the focal point of an experiment lies in choosing not to need drawing the conductive line surface finish and dealing with the way to change different BGA solder pads metal surface finish and to cooperate with uses of a lead-free solder ball, such as Sn-3.5Ag-0.5Cu and Sn-7.0Zn-100ppmAl at the electron industry under this experiment. And, BGA solder pads metal surface finish is it chosen for 3 kinds to deal with. That is, OSP (Organic Solderability Preservative), ENIG (Electroless Nickel Immersion Gold), & the chemical silver (Immersion Silver) are carried on every experimental analysis and discussed.
Analysis for different BGA solder pads surface finish and lead-free solder ball combine with solder joints , that after the IR Reflow carrying on the aging experiment of the high temperature mainly. Through x-section, to analyze the state that IMC grows up, and it carried on the shear force to search for solder joints reliability to check which metal surface finish was the best choice. Then, to analyze which surface finish has its own advantage and disadvantage for the root cause of low shear force and to check metal growing up and interface analysis of reacting of every experiment. Moreover, the experimental result is summed up for the main conclusion as follows:
1.It was found different surface finish by solder ball shear force. Although, the Sn-3.5Ag-0.5Cu were influenced by temperature, reduction did not change on various surface finish effects. It was the most significant for low shear force that it influenced dealing with OSP copper and chemistry silver surface finish among them that the Sn-7.0 Zn-100ppm Al would be dealt with by different kinds of surface finish.
2.To observe Sn-7.0 Zn-100ppmAl solder ball & IMC growing-up state of ENIG and OSP copper surface finish, it was found that OSP copper surface finish growing up with time and temperature fast. Nonetheless, ENIG glowed up slower. It was shown that the layers for hindering nickel was more adiabatic to spread and diffusion between metal not to spread quite obviously. Based on above analysis, it was found OSP higher than ENIG. Due to that reason, it could get stable shear force by ENIG surface finish.
3.In addition, it was found that a Sn-7.0 Zn-100ppm Al solder ball shear force OSP and chemistry silver surface finish dealt with 120oC under 1000 hours was it produced that solder pads copper face was copper etching condition . As temperature rises, it condition seriously causes solder joints shear force reduced.
4.The chemistry silver surface finish was observed for the obvious larger micro voids, but other finish surface interfaces had a ‘Kirkendall Voids’ problem obviously even under this experiment. Nevertheless, relative solder joint & reliability silver surface were they had heavy risk to deal with.
In conclusion, a result of study shows it needs very carefully that Ball Grid Array solder pad surface finish and selection of lead free solder ball. It was finally found with an experimental result that we can give to arrange in order from follow: Sn-3.5 Ag-0.5Cu+ ENIG P%> Sn-3.5Ag-0.5 Cu+ OSP> Sn-3.5Ag-0.5Cu+ Im-Ag > Sn-7.0Zn-100ppm Al+ ENIG P%> Sn-7.0Zn-100ppm Al+ OSP >Sn-7.0 Zn-100ppm Al+ Im-Ag . That is main a reason Sn-7.0 Zn-100ppm Al collocated OSP copper face or chemistry silver surface was apt to appear solder ball shear force reduced & insufficient solder-joint strength. Moreover, It was also found copper etching due to high diffusion reaction. In brief, those kinds of combination should not used for are high reliability electronic package construct.
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