焊球的形成机理及去除方式研究

Formation mechanism and removal method of solder balls

焊球是构成焊膏的合金焊粉在烧焊时形成的可移动的金属颗粒物,粒径与焊粉相当,会对电路的可靠性造成不利影响,更会直接造成混合集成电路颗粒碰撞噪声检测(PIND)失效。依照IPC-TM-650测试方法手册2. 4. 43条给出的焊球测试的试验方法和测试标准,通过对比焊粉尺寸、焊膏是否含铅、焊膏印刷后静置时间及烧焊过程中是否通氮气对焊球产生的不同影响,阐述和论证了焊球形成的机理是焊膏吸湿和氧化,并指出在工艺生产中焊膏印刷或喷印时容易造成焊球生成的环节。焊球产生后会包裹在助焊剂中,但不会随着助焊剂的清洗而完全消除,会因静电原因继续吸附在基板上,待静电得到释放后,可采用高压氮气枪吹洗的方式有效去除。

Solder balls are mobile metal particles formed by the metal powder of solder paste during the welding. The particlesize of solder balls is comparable to that of the solder powder. It has an adverse impact on the reliability of the circuit, directly leadingto the failure of hybrid integrated circuit PIND （particle impact noise detection. The test methods and standards for the solder ball inthe IPC -TM - 650 manual No. 2. 4. 43 were used in this work. We demonstrates that the formation of solder ball is due tomoisture absorption and oxidation of the solder paste. Here comparison was made for the effects caused by four factors, including thesize of the solder powder, the lead composition of solder paste （both for lead and lead-free）, the standing time after the solder pasteprinting, and the usage of nitrogen gas during the reflow process. In this work, the factors that cause solder ball formation werestudied for both solder paste printing and jet printing. Solder ball will be contained in the flux after welding, and would not becompletely removed during the flux removal. It is adsorbed on the substrate due to static electricity. It can be removed by highpressure nitrogen when static electricity is released.