Dicing Low-K Materials

Dicing Low-k materials is challenging.  The conventional approach using one or multiple dicing blades created issues of front side chipping or layers would peel away causing device failure.  In an article in 2004 Synova proposed a full cut approach using a laser cooled by water.

ST Micro Synova Water Jet Laser Dicing Article

Below is an example of the results which are quite impressive indeed on a low-K wafer.

ADT and Disco both developed approaches whereby the wafer is grooved with a laser and then the wafer is diced using a mechanical blade.

  

Disco Low-K Dicing

 ADT Low-K Dicing

Low-k materials requires a new approach to singulation.  What is often missed in discussions on singulation is dicing tape.


Dicing tape is more than a "sticky support" for a water jet application the wrong dicing tape will cause dies to fly off and for the groove and dice solution dicing tape plays a critical role as the wrong tape could cause backside chipping or die fly off.  If you have any questions regarding which tape might be right for your process please contact me.

Dicing Tape for Various Applications

DBG Process

The conventional dicing process consists of mounting a wafer on to a medium (wax or tape) and then connecting either to a hoop ring (set of concentric expansion rings) or a ring frame (either stainless steel or plastic) and then dicing through the material.  In the conventional process the dicing process is the process of singulation where a chip or die is separated from the wafer.  Their are issues with this process which affect yield.

One of the largest of these issues is backside chipping.  Backside chipping has many potential root causes but the effect is the same lower die strength.

  

 A Study on Chip Thinning Process for Ultra Thin Memory Devices (Toshiba)

Link to the Toshiba White Paper

The chart above is a test on dies ranging from 10um to 25um thick.  The results clearly demonstrate that backside chipping (conventional) reduces die strength.  Reduced die strength may result in failure during subsequent steps in ultra-thin chips.  So what is the answer?

One potential answer is DBG (Dice Before Grind).  This process was developed in 1999 by Toshiba and two suppliers stepped up to deliver the solution Disco Corporation and LINTEC Corporation.
1999 DBG Press Release

 Flash Movie Showing DBG Process

The above illustration shows the steps in the DBG process.  Disco supplies the half-cut dicer (blades) and grinder (grind wheels) and LINTEC supplies the back grind tape laminator (back grind tape) and wafer mounter (pick-up tape).  Links to all of the products are listed below.

Back Grind Tape Laminator and Mounter
Half-Cut Dicer and Grinder

Investing in new systems may not be cost effective for smaller companies so there are vendors who offer to process DBG wafers.  Contact me for a list of companies who can supply this service.  In addition this process can be done using manual equipment on a smaller scale.  I can not publish the results or technique here but it there has been significant data collected using semi-auto Disco and LINTEC equipment and if you contact me I would be happy to help design a more cost effective process for lower wafer volumes.

The decision to use the DBG process really depends on the thickness of the die, the package design, and the effect chipping (front side and back side) have on device performance.  DBG may not be for every application, but for applications requiring ultra-thin strong dies it will increase die strength and ultimately positively impact yield.