19 December 2014
Copper Pillar is rapidly being adopted as a bumped wafer interconnect. The construction is that of a Copper cylinder around 50µm in diameter and height, topped with a dome of solder.
As with any interconnect the quality of the bonding process between the different parts is vital for the reliability of the finished product. The bond between the copper and its pad on the wafer are of particular interest as this is seen as the most likely failure mode. In a bond test a failure mode between the copper and wafer is then the “Failure mode of interest”.
This failure mode can be produced by either a pull or a shear test and the measured bond strength used for your process control. In many other applications pull testing is typically preferred because the bond is subjected to a simple tensile load, distributed over the bond area. The bond separation is clean making failure mode analysis of the surfaces relatively easy. Unlike solder bumps, Copper is relatively hard and gripping it therefore easier.
Solder balls require precise reforming in order to be able to apply a meaningful test load on to the bond. Copper also has to be reformed in order to be able to grip it but this takes the form of well know gripping methods such as plain surfaces and friction, a few serrations that slightly reform the copper in order to get a mechanical grip or a slight tapper.
An alternative to pull testing is a shear test. If this is done with a very low shear height the bond is subjected to mostly shear. If a high shear height is used the bond is loaded by shear and a bending moment. It is though the bending loads, and in particular the tension side of the bending moment, that typically cause the bond to fail. The pillar tends to pivot on its edge furthest from the shear tool, making the failure mode very similar to that of a pull test.
The advantages of a high shear test are that the tool and test are much simpler. Making pull tweezers with 50µm cavities is difficult and costly. Aligning them to the pillar takes time and requires skill. A shear test is no different to that commonly used when testing wire bonds. The only difference being the shear height is bigger. The tools cost a lot less and its alignment to the pillar is not so critical, making it less skilled and faster.
Variations in shear height will cause variations in the test result but with the Condor Sigma accuracy of ±1µm these affects are likely to be less than those caused by the grip reforming and operator misalignment in a pull test. It is though beneficial to test with the highest possible shear height as this reduces any effect from the small variations in height and assures that the bending moment dominates the failure mode.
For a solder ball a Cold Bump Pull test is known to be better than shear. A 1st bond Gold ball test is best done with a low shear height. The reason for both of these comes from our “Golden rules of bond testing” ©, they both produce the highest number of failure modes of interest or the highest possible test force.
In the case of Copper pillars we should be guided by these same rules. Shear is the simplest test and it does produce the failure mode of interest. The optimum shear height will be the one that maximises this or produces the highest test force.
The choice between pull or shear testing depends on the application and the test objectives. If you are interested to find out more please contact us for more information, to request a demonstration or a quotation.
|Jul 2017||Advances in Thin, 3D and MEMS Die Bond Strength Testing|
|May 2017||Shear testing copper pillar|
|Mar 2017||Fracture strength of thin wafers and die|
|Feb 2017||Centralized database for enhanced security and SPC options|
|Jan 2017||Full Automation with Improved Pattern Recognition, Fiducial Marks Analysis, Wire Detect and Failure Mode Analysis|
|Dec 2016||Coating and film testing|
|Nov 2016||Latest software release enables automatic grading|
|Oct 2016||Vision enhanced materials testing|
|Sep 2016||XYZTEC makes lid pull easy|
|Aug 2016||Condor Sigma W12 with large heater stage|
|Jul 2016||How to: Wire Pull|
|Jun 2016||Get 10% off your next tools order|
|05 Jun||Visit us at SMT Hybrid Packaging Nuremberg|
|20 Apr||Smart LED and Solar panels for XYZTEC head office|
|18 Apr||XYZTEC workshop at IMAPS UK|
|16 Mar||ODEOM shows Condor Sigma in Istanbul|
|15 Mar||Semicon China under way|
|31 Jan||Condor Sigma W12 at Semicon Korea|
|04 Dec||Condor Sigma stars in Audi Tech Day video|
|10 Nov||Raysun to represent XYZTEC in China|
|23 Oct||Award for First Technology China|
|19 Jul||XYZTEC granted subsidy for further accuracy improvements|
|23 Jun||Presentation at CSPT 2017 by Bob Sykes|
|06 Jun||Condor Sigma in São Paulo, Brazil|
|16 May||Fully automatic lead frame tester introduced at SMT Hybrid Packaging|
|28 Apr||Semicon Penang 2017 successful|
|28 Apr||Pizza and Go cart racing at K1 Speed in Northern CA|
|14 Mar||Visit us at Semicon China|
|16 Feb||Job opening for Junior Mechanical Design Engineer [closed]|
|29 Nov||Successful seminar in Russia with Sovtest|
|31 Oct||Market leading Condor Sigma bond tester at TPCA Taiwan|
|08 Sep||Automation features draw attention at Semicon Taiwan 2016|
|28 Jun||HTMG represents XYZTEC in South America|
|14 Jun||Bob Sykes speaks at China Semiconductor Packaging Test Symposium (CSPT) [UPDATED]|
|14 Jun||Purchase wire hooks, shear tools, tweezer tips by PayPal|
|03 May||SMT 2016 all about automation|
|11 Apr||Annual sales and service event in Bangkok big success|