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Abstract
The capillary under-fill (CUF) process is a procedure of applying a thin layer of epoxy using capillary technique to attach a flip chip onto a substrate. Epoxy shot weights and peak temperatures are two main variables used to control this process and detect inconsistencies in epoxy dispense. These variables are co-monitored primarily to ensure constant epoxy dispense for quality assurance. Inconsistent epoxy dispenses detected by out-of-control shot weight and peak temperature measurements become an issue as permanent chip attach is based on a constant layer epoxy on the substrate. This paper identifies some of the most important root causes of inconsistent epoxy dispense and proposes possible and achievable solutions towards ensuring the quality control of the mass-produced units passing through the capillary under-fill process.
Keywords
Industrial Engineering, quality control, epoxy, capillary under-fill (CUF) process, flip chip application.
.1. Introduction
The integrated circuit (IC) technology has deep roots that go back to the 1950s. Today, functions and applications of this technology has been quadrupled and thus the birth of miniature IC chips called microprocessors that support almost all modern electrical devices from computers to automobiles. Connection methods for these microprocessors were categorized into three basic approaches in the 1960s and have not changed much five decades later. These approaches were wire bonding, chip carriers with beam leads and direct chip connection. IBM researched direct chip connections in the 1960s and came across major issues with joint degradation. After years of improvising, this mode of connection was possible with the help of moisture resistant sealants called epoxies. With the introduction of flip chips, the capillary underfill (CUF) action was the ideal method to draw the epoxy under the tiny chips. Due to the extremely small underfill space, the amount of epoxy dispensed is a critical factor. Insufficient epoxy dispense would lead to an inconsistent spread of the epoxy under the chip, causing some joints to be exposed to moisture. An overload of epoxy dispense however, would lead to die flooding, where part of the surface chip is covered by epoxy, causing unit defects [1]. The two variables, which are controlled to detect the possibility of inconsistent epoxy dispense are epoxy shot weight and peak temperature.
Epoxy shot weight is the weight of epoxy per shot...