Image Analysis as an Aid to Quantitative Interpretation of Acoustic Images of Die Attach

Die attach involves bonding a silicon chip to a substrate or lead frame using one of several methods; eutectic, adhesive material, or solder. Good adhesion of the die is critical in order to provide both mechanical stability of the component and uniform heat dissipation in the circuit. Voids or disbonds at the die attach interface reduce the power dissipation capability which can result in interruption of the proper operation of the component. The SLAM (Scanning Laser Acoustic Microscope) has been used successfully to nondestructively image the die attach interface. The SLAM is very sensitive to laminar flaws such as disbonds or voids in a die attach bond. The SLAM, however, produces a through-transmission image and as such, does not necessarily give the exact depth at which the flaws occur. The C-SAM (C-Mode Scanning Acoustic Microscope) is a reflection mode device and as such, is capable of focusing at different levels within a sample to determine the exact depth of a flaw. Qualitative information is easily obtained from acoustic images as to the presence and location of voids or disbonds in the die attach. In many cases it is neccessary to obtain quantitative information from the qualitative images. The current MIL-SPEC states that only those disbonds which cover a certain percentage of the bond area qualify as failures (Figure 1). Also, quantitative information provides for an objective determination of bond quality, and allows for computer decision of acceptance in automated production applications. In order to derive the quantitative information, image analysis is used. Simple routines can be used to determine the area fractions of the bond and disbond. Other routines can be used to analyze the contrast in the image and to measure the ultrasonic attenuation in the bond area. Examples of how image analysis has been used to aid in the interpretation of acoustic images of die attach bonds will be presented.