回流气氛对无助焊剂倒装焊焊点气孔的影响

Influences of Reflow Atmospheres on the Solder Joint Voids of the Fluxless Flip-Chip Bonding Process

研究了不同回流气氛对无助焊剂倒装焊焊点气孔的影响,并分析了氮气、甲酸回流气氛对密封腔体内部气氛含量的影响。研究结果表明,使用甲酸去除倒装芯片焊点表面氧化物后,电路在氮气环境中回流,焊点未产生气孔,且内部气氛能满足国标要求。在回流峰值温度持续时间内保持甲酸浓度不变,也可有效避免焊点气孔产生,但内部气氛含量中二氧化碳和氢气超标。在回流峰值温度持续时间内,真空环境时,因焊料金属氧化物无法充分还原成金属单质,且加热效果不理想,焊点位置易产生气孔,发生率约50%。实际生产中,在回流峰值温度区间先通入甲酸后抽取真空的方式可有效避免气孔产生。

The effects of different reflow atmosphere on the solder joint voids of fluxless flip-chip bonding process were studied,and the influences of the reflow atmosphere of nitrogen and formic acid on the internal atmosphere content of the sealed cavity were analyzed.The research results show that after removing the solder surface oxides of the flip-chip with the formic acid,the circuit reflows in N_2 atmosphere,the voids are not generated in the solder joint,and the internal atmosphere of the circuit can meet the national standard.The formic acid concentration remains constant in duration of the reflow peak temperature,and the solder joint voids can also be effectively avoided,but the CO_2 and hydrogen contents of the inside atmosphere exceed the standard.With the vacuum environment in duration of the reflow peak temperature,the voids are easily generated in the solder joint because the reduction reaction of the metal oxide is inadequate and the heating effect is unsatisfactory,the incidence rate of the voids is about 50%.In the actual production,the method of passing formic acid firstly and then extracting vacuum can effectively avoid the production of the voids in the reflow peak temperature range.