Laminated Die Stiffener for Flexible Applications
Brant Besser
Steve Strouse
Ken Thompson
In modern flexible electronics applications, such as smartcards and RFID tagging, there is an increasing need for increased functionality. Higher device functionality generally results in larger semiconductor die. Mechanical stresses on the semiconductor die increase greatly as the size of the die increases. This stress results in semiconductor fracture and consequently failure of the electronic device. Designers of these flexible electronic devices are therefore forced to trade off decreased reliability of their product for increased computing power.
This paper discusses the use of a die stiffener laminated to the back side of the semiconductor die for increased fracture resistance.
In order to achieve stiffening of the semiconductor die, the die is mounted to a carrier made of a material of greater rigidity and less fracture prone than the semiconductor die material. The designer has a large choice of material in which to build the die stiffener. These materials could be metal, plastic or glass/ceramic or any combination of these that achieves the desired rigidity. The semiconductor die would be thinned to accommodate the thickness of the stiffener so that the resulting unit would be approximately the same thickness as the originally intended die. The semiconductor and the die stiffening material are subsequently laminated using an appropriate method of adhesion. The result is a form, fit and function replacement for an original semiconductor die that would have been used in the application, but demonstrates much greater resistance to die failure related to mechanical stresses.
There are several advantages to this methodology for die stiffening over other methods of fracture toughening of a flexible electronics application. Most fracture toughening methodologies require stiffeners placed in the flexible card or board material around the semiconductor die in order to avoid bending at the semiconductor. This requires each device being built to have the stiffener installed individually which is difficult to automate and often requires redesign of the equipment when it is determined that the stiffener is required. Laminated Die Stiffeners however, may be added anytime during the design or assembly cycle without affecting the original design or assembly equipment. Laminated die stiffeners may also be done in batch at the wafer level prior to sawing, thereby reducing recurring cost.
