meixinjiance
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- 2015-03-11
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发表于 2015-03-17 17:22
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焊接不良失效分析1. 案例背景ØZÆTë ybbs.3c3t.comã¡O,å1½ÄX公司出现了一批某型号的手机,品质部门反馈手机软板上SMT元件焊接后易脱落,不良率约为3.3%,PCB焊盘上的断裂面在电子显微镜下观察,表现为平整的断裂面。ØZÆTë ybbs.3c3t.comã¡O,å1½Ä2.分析方法简述ØZÆTë ybbs.3c3t.comã¡O,å1½ÄØZÆTë ybbs.3c3t.comã¡O,å1½ÄA.样品外观照片:ØZÆTë ybbs.3c3t.comã¡O,å1½ÄØZÆTë ybbs.3c3t.comã¡O,å1½Ä ØZÆTë ybbs.3c3t.comã¡O,å1½ÄØZÆTë ybbs.3c3t.comã¡O,å1½ÄB.确定了试验方案后我们针对失效样品做了如下的分析:ØZÆTë ybbs.3c3t.comã¡O,å1½Ä ØZÆTë ybbs.3c3t.comã¡O,å1½ÄØZÆTë ybbs.3c3t.comã¡O,å1½Ä备注:AuSn4是一种很脆的金属间化合物,是引起“金脆”现象的主要原因﹐对焊点强度影响较大。ØZÆTë ybbs.3c3t.comã¡O,å1½Ä ØZÆTë ybbs.3c3t.comã¡O,å1½Ä ØZÆTë ybbs.3c3t.comã¡O,å1½Ä ØZÆTë ybbs.3c3t.comã¡O,å1½Ä ØZÆTë ybbs.3c3t.comã¡O,å1½Ä ØZÆTë ybbs.3c3t.comã¡O,å1½ÄC.找到导致焊点易脱落的失效机理后,与该公司工艺人员沟通后,得知其焊接时的TOL长达70s,但由于该款产品即小又薄,且零部件布局密度也较低。这样过长的TOL时间导致焊点IMC结构粗大、松散,富P层过厚并形成了Ni-Sn-P层。ØZÆTë ybbs.3c3t.comã¡O,å1½Ä3. 分析与讨论ØZÆTë ybbs.3c3t.comã¡O,å1½Ä由以上分析结果可以导致焊点易脱落的原因是多方面因素造成的,总结如下:ØZÆTë ybbs.3c3t.comã¡O,å1½Äa). 失效元件的焊点形成了大结构的(Ni,Cu)3Sn4 IMC,过多的易脆的IMC的生成会导致焊接强度偏低,在受到应力时焊点容易在IMC于PAD上的富P层之间开裂。ØZÆTë ybbs.3c3t.comã¡O,å1½Äb). 同时焊点的富P层也很厚,富P层内由于Ni扩散而形成的裂缝会降低焊点的强度。ØZÆTë ybbs.3c3t.comã¡O,å1½Äc). 焊点焊接界面附近残留的AuSn4合金(可能是PCB PAD金层过厚或焊点锡量过少不利Au的熔融导致),这种合金可能会引起“金脆”,对焊点强度也有一定影响。ØZÆTë ybbs.3c3t.comã¡O,å1½Äd). 焊点在富P层与(Ni,Cu)3Sn4 IMC间形成了对焊接强度危害极大的Ni-Sn-P合金,焊点的断裂主要发生在Ni-Sn-P层附近。ØZÆTë ybbs.3c3t.comã¡O,å1½Ä4.结论ØZÆTë ybbs.3c3t.comã¡O,å1½Ä减少回流时间到45s~55s,以抑制Ni-Sn-P层的形成,减少焊点IMC、富P层厚度。改善PCB表面处理制程,杜绝“黑镍”现象发生。减薄PCB PAD金层厚度或增加焊点锡量以防止“金脆”发生。ØZÆTë ybbs.3c3t.comã¡O,å1½Ä 备注:回流时间越长会生成越多的Ni-Sn-P合金。ØZÆTë ybbs.3c3t.comã¡O,å1½Ä 5. 参考标准ØZÆTë ybbs.3c3t.comã¡O,å1½ÄIPC-TM-650 2.1.1-2004手动微切片法ØZÆTë ybbs.3c3t.comã¡O,å1½ÄGB/T 17359-2012电子探针和扫描电镜X射线能谱定量分析通则ØZÆTë ybbs.3c3t.comã¡O,å1½Ä作者简介:ØZÆTë ybbs.3c3t.comã¡O,å1½Ä ØZÆTë ybbs.3c3t.comã¡O,å1½ÄMTT(美信检测)是一家从事材料及零部件品质检验、鉴定、认证及失效分析服务的第三方实验室,网址:www.mttlab.com,联系电话:400-850-4050。ØZÆTë ybbs.3c3t.comã¡O,å1½Äwww.mttlab.net ØZÆTë ybbs.3c3t.comã¡O,å1½ÄØZÆTë ybbs.3c3t.comã¡O,å1½Ä ØZÆTë ybbs.3c3t.comã¡O,å1½Ä
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