Die Scratch

Die Scratching

Die scratching is a failure mechanism wherein the surface of the die is mechanically damaged by a rigid object that is accidentally dragged across or moved over it. Die scratching usually results in gross abrasion, scraping, or laceration damage on the die's active circuit (see Figure 1). The damage itself is referred to as a 'die scratch', while the damaged die is referred to as a 'scratched die.'

Die scratches are caused by mechanical means, usually by mishandling. 'Mishandling' in this context also includes the improper or careless use of tools and accessories used by an operator while working. It is common to see die scratches that resulted from a pointed object such as a probe needle or tweezer accidentally touching the die and sweeping across its surface.

Scratches that reach the active circuit beneath the glassivation will immediately lead to electrical failure due to shorted and open metal lines. Metal shorts are commonly seen in narrowly-spaced metal lines, wherein the displaced metal materials bridge the lines together. Open circuits are often induced in narrow, isolated lines.

Shallow scratches on the die that do not reach the active circuit will not cause immediate electrical failure, but may pose reliability risks if the top passivation has been breached. For instance, the seepage of moisture and contaminants through a damaged portion of the glassivation can result in die corrosion.

Figure 1. Optical photo (left) and SEM photo (right) of die scratches

Die scratching can occur anywhere from wafer fab to assembly prior to encapsulation. Picking up a die carelessly with a tweezer for eutectic die attach can result in the tweezer slipping out of position while scratching the die surface. Improper equipment set-up can cause probe needles, die overcoat dispense tools, and the like to land on and scratch the surface of the die.

Foreign materials and dirt embedded at the pick-up tool tips of pick-and-place machines during die attach can also cause die scratches. Similarly, the use of defective, worn-out, or damaged pick-up tools can scratch the die surface. Manual capping of ceramic packages prior to sealing may also cause a die scratch, if the cap or lid inadvertently gets into contact with the surface of the die.

Die scratches are quite easy to confirm by optical microscopy, since they truly resemble scratches seen everyday in common objects.

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