A Study on the Phase Equilibria and Interface Reactions between Nickel and Bismuth for Lead-Free Solders Applications

• Main Authors: Lee, M. S., 李明勳
• Other Authors: C. R. Kao
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/33004703247322826663

碩士 === 國立中央大學 === 化學工程學系 === 86 === Two sets of experiments were carried out in this work. The first is thereaction between solid Ni and liquid Bi, and the second is the reactionbetween solid Ni and solid NiBi3. Bismuth is an important ingredientin many electronic lead-free solders, while Ni is used in many PrintedCircuit Board (PCB) and Ball Grid Array (BGA) package surface finishes.In solid/liquid reaction, experiments were carried out at 300, 360, 420,and 480 oC for 10~360 minutes. It was found that a reaction zone formedbetween Ni and Bi. The reaction zone is a two-phase mixture of NiBi3 needles dispersed in Bi matrix. The other intermetallic compound NiBi,which is thermodynamically stable at these temperatures, did not formed.In addition to the NiBi3 formed within the reaction zone, NiBi3 alsoformed outside the reaction zone as long needles with hexagonalcross-section. It is believed that these NiBi3 needles formed duringthe solidification of liquid Bi. Reaction at 300 oC produced athick reaction zone, and the thickness of the reaction zoneincreased rapidly with reaction time, reaching 400 mm after 360minutes. Reactions at 360 oC and 420 oC produced very thin reaction zones. At high reaction temperatures, the amountof NiBi3 outside the reaction zone increased rapidly. Nickeldisk of 0.5 mm thick was fully dissolved into liquidBi in 20 minutes. It is proposed that the formation of thereaction zone is controlled by two factors: the solubility limit and the diffusivity of Ni in liquid Bi. At higher temperature, both diffusivity and solubility limit are higher and tend to favor the formation of thin reaction zone.In solid/solid reaction, experiments were carried out at 330, 370, 410,and 450 oC for 150~600 hours by using diffusion couples. It was foundthat NiBi with layered structure formed between Ni and NiBi3. Analysisusing EPMA showed NiBi has the composition of 51*0.7 at. % Bi. AlthoughNiBi did not form when Bi was reacted with Ni, NiBi did form when Biwas reacted with NiBi3 at 450 oC. This observation seems to indicatethat nucleation of NiBi is not a rate determining step, and thereason for the missing of NiBi is due to kinetics. The growthof NiBi layer was diffusion controlled with an activation energyof 84.4 kJ/mol. Marker experiment showed that both Bi and Niatoms diffuse, but Bi atoms diffuse a little bit faster thanNi atoms.