Wafer Direct Technology for Mini LED Flip Attachment

We would like to introduce the mechanism structure of our wafer direct die attachment technology for mini LED. Wafer direct technology is structured from two parts of that one is adhesive one shot dipping and other is pinhole free chip shooting. 1st, we developed “One shot wafer dipping” which can transfer the adhesive to around 30,000 chips of mini LED on a wafer at once. Second section is to take about die mounting. Common die bonder use an ejector pin to pick up mini LED chip. Ejector pin makes a pinhole on wafer and lead air into between wafer and mini LED chip. This air is effective to remove mini LED chip from wafer by the pick up nozzle. Ejector pin of die bonder leaves a broken piece of wafer on chip. We developed wafer direct chip shooting technology. Wafer direct chip shooter also use an ejector pin for shooting down mini LED chip. But wafer direct does not make any pinhole on wafer that means no broken piece of wafer exists. Our wafer direct technology maximize productivity of mini LED die bonding and minimize faulty ratio of mini LED die bonding.

Epoxy Die Attach Combined With Face-Up Die Bonding for Improved XYZ Placement Accuracy

Epoxy die attach is widely used in microcircuit assembly and enjoys advantages such as ease of deposition, fast curing, reworkability, and non-toxicity. These qualities also make it suitable for automated mass production. However, this method falls short when high placement accuracy is desired as the die can shift on uncured epoxy leading to die displacement from its original location. Gold to gold face-up bonding is another method utilized in microelectronics packaging given its proven bonding reliability and high placement accuracy for small devices. Nevertheless, it is difficult to achieve a reliable bond using this method for relatively larger devices. The nonplanarity of the bonding collet or the variation in the height of the gold bumps results in a tilted die attach and/or a weak bond between the die and the substrate. Moreover, CTE (Coefficient of Thermal Expansion) mismatch between the die, the gold bumps, and/or the substrate leads to bond failure due to temperature fatigue. This paper discusses a hybrid method to take advantage of the strengths of both methods mentioned above, culminating in a reliable process with high XYZ placement accuracy. To apply this method, epoxy is first dispensed on a gold-plated substrate. Using a flip chip machine, samples with plated gold bumps on their ground side are then placed on the substrate. The gold bumps are mainly used as targets and stand-offs to improve the placement accuracy and to control epoxy glue-line thickness. The force applied on the die, the time the force is applied, and the substrate temperature are controlled for optimum die attach. Moreover, along with the force applied by the vacuum tip, epoxy is partially cured on the flip chip machine heated stage before it is moved to an oven to complete the cure process. Die shear test results before and after temperature conditioning are compared with standard epoxy die attach and gold to gold face-up bonding for identical samples and the advantages are discussed.

Multi-Hole Process Plate Modification for Chip on Lead Device at Die Attach Process

The paper focused on the improvement done in chip on lead (COL) leadframe package assembly manufacturing to address the leadframe bouncing effect during die attach process. A new and enhanced process plate is designed with multi-hole configuration to provide a strong vacuum underneath the leadframe and to maintain the planarity during dispensing and die bonding of silicon dies onto the leadframe. With the new multi-hole process plate, leadframe bouncing was successfully eliminated during die attach process. For future works, the multi-hole process plate could be used on devices with similar configuration.