Copper pillar 铜凸块测试


Friction grip
Friction grip

介绍

Copper Pillar 被快速应用在晶圆凸块制程. 基本结构是50μm直径和高度的同柱体, 顶端有圆顶状的锡.

Reformed solder ball
重塑锡球

在bonding制程,有关两个不同物件的任何内部连结的品质对于最终产品的可靠性是非常重要的. 在铜和它的pad在wafer上的连结处,所产生的失效模式更是我们特别关心. 因此测试铜柱和wafer间的连结,是我们有兴趣知道的失效模式.

Pull test copper pillar gripped with two tapered cavities
使用两个锥形夹爪对铜柱进行拉力测试

在铜和它的pad在wafer上的连结

拉力测试

失效模式可以透过拉力或推力测试来产生, 而测量值可以被使用当成制程管控. 在很多其它的应用,拉力测试是很典型被多数人采用, 因为连结处主要跟分布在连结处的张力负载有关. 当连结处被分开的很乾净,可以很容易的在表面作失效模式的分析. 不同于锡凸块, 铜柱是相对的比较硬,因此也比较容易夹住测试.

Example of typical pull test results for Copper pillar
范例:典型的Copper pillar铜柱拉力测试结果

锡凸块为了在测试中,需要非常精准的重塑动作,为了是提供连结处有意义的测试负载. 铜也是需要做重塑动作,为了是可以夹住它,但是我们都知道夹持在光滑,无摩差力的表面, 我们需要一些锯齿状来重塑铜柱, 来得到机械式的夹持.

Failure mode P1
失效模式P1

推力测试

另外一个取代拉力测试的方式是推力测试. 假如他可以设定非常低的推力高度来执行测试时, 连结处会承受大部分的推力. 假如推力高度设定的比较高,该连结处会同时承受推力和弯折情况. 虽然有弯曲的负载,特别在弯曲张力侧, 会典型的造成连结处失效. 铜柱会以最远端当支点被推刀转动, 这造成了失效模式非常相似与拉力测试.

Copper pillar low shear height and bond fails in shear
Copper pillar 铜柱低的推力高度, 连结处失效在推力

设定高的推力高度的优点是推刀和测试会简单很多. 使用50μm的夹爪做夹拉测试是困难和高成本的. 在工具与铜柱的对位上是比较花时间和需要技巧的. 使用推力测试上与现有的金线连接端推力测试是一样的. 为一不同的是推力高度比较高. 工具成本低很多而且在执行对位上也比较容易, 不需太多技巧并且快速.

Copper pillar high shear height and bond fails in tension
Copper pillar铜柱高的推力高度,连结处失效在张力

推力高度的变异量将会影响测试结果的变异量,但是因为 Condor Sigma 精度在 ±1μm ,所以这些影响很可能少于在拉力测试中, 执行夹持时的重塑动作或是操作员对位不准的错误. 虽然这是有帮助的,当测试高度越高越好,可以减少任何来自推力高度变异的影响,并确保弯曲现象掌控失效模式.

Example of typical shear test results for Copper pillar
范例: 典型的Copper pillar推力测试结果

针对锡球, 做CBP夹拔锡球测试 是已知比推力还好的测试. 针对金线的第一焊点的测试, 它的推力高度是尽可能的设低一些. 这两者的原因主要是来自我们的 “焊点测试的黄金守则" ©, 他们都可以产生最大量我们有兴趣的失效模式或是测试结果的最大值.

Failure mode S1
失效模式 S1

在Copper pillars 铜柱的这个案例, 我们应该使用相同的守则. 推力是最简单的测试并且可以产生我们有兴趣的失效模式. 最佳的推力高度将会是其最大值或着是可以产生最大测试值的高度.

 


 
 

This shape of solder is possible to test similar to regular Cold Bump Pull (CBP)
This shape of solder is possible to test similar to regular Cold Bump Pull (CBP)
The solder interconnect is very difficult to test. Shear is the best test
The solder interconnect is very difficult to test. Shear is the best test

Solder to copper interconnect

拉力测试

If you are interested in the interconnect between the solder and the copper, it depends on the shape of the construction whether a Cold Bump Pull (CBP) type test is feasible. If not, a shear may be the only effective test to qualify your process.

More on CBP can be found in our how-to.

The test sequence for the CBP-approach is as follows:

Copper pillar test sequence for solder interconnect using CBP
Copper pillar test sequence for solder interconnect using CBP

推力测试

As with any shear test, testing the solder to copper interconnect requires accurate alignment of the shear tool to the bond line. When the height of the bond line from the substrate varies due to tolerance build up conventional shear height methods can be a problem.

Tolerance build up can cause problems when shear testing the copper bump using conventional methods
Tolerance build up can cause problems when shear testing the copper bump using conventional methods

A solution is XYZTEC’s unique top landing shear method. The tool lands on the top of the solder, then moves back and down programmable amounts to guarantee a shear height relative to the top of the pillar rather than its base.

The test sequence using XYZTEC’s unique top landing shear method
The test sequence using XYZTEC’s unique top landing shear method

The video below shows a test. The programmed landing force is 5gf. As the landing contact is initially a point, even with a low landing force, a small amount deformation occurs on the top of the solder. The loads on the pillar bond though are small and compressive and have no detrimental effect on the measurement. The Condor Sigma is the only bond tester in the world with a programmable landing force and is capable of lower landing forces than any other tester.


选择拉力或是推力测试

要选择拉力或是推力测试, 主要是根据应用和测试主题. 如果你需要更多的资讯, 请联络我们 , 来做机台展示或是报价.


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