Search

The miniaturization of microchips is always driving force for revolution and innovation in the electronic industry. When the pitch of bumps is getting smaller and smaller the ball size has to be gradually reduced. However the reliability of smaller ball size is getting weaker and weaker, so some traditional methods such as capillary underfilling, corner bonding and edge bonding process have been being implemented in board level assembly process to enhance drop and thermal cycling performance. These traditional processes have been increasingly considered to be bottleneck for further miniaturization because the completion of these processes demands more space. So the interest of eliminating these processes has been increased. To meet this demand, YINCAE has developed solder joint encapsulant adhesives for ball bumping applications to enhance solder joint strength resulting in improving drop and thermal cycling performance to eliminate underfilling, edge bonding or corner bonding process in the board level assembly process. In this paper we will discuss the ball bumping process, the reliability such as strength of solder joints, drop test performance and thermal cycling performance.

Solder joint encapsulant adhesives have been successfully used to enhance the strength of solder joints and improve thermal cycling as well as drop performance in finished products. The use of solder joint encapsulant adhesives can eliminate the need for underfill materials and the underfill process altogether, thus simplifying rework, which results in a lower cost of ownership. Solder joint encapsulant adhesives include: low temperature and high temperature solder joint encapsulant adhesives, and their derivatives. Each solder joint encapsulant adhesive has: unfilled and filled solder joint encapsulant adhesives, and solder joint encapsulant paste. Each solder joint encapsulant product has been designed for different applications. In this paper, we are going to discuss the details and future of solder joint encapsulant adhesives.

Silicon dioxide is normally used as filler in underfill. The thermal conductivity of underfill is less than 1 w/mk, which is not able to meet the current flip chip application requirements such as 3D stacked multi-chips packaging. No matter which direction the heat will be dissipated through PCB or chip, the heat has to pass through the underfill in 3D stacked chips. Therefore the increase of thermal conductivity of underfill can significantly enhance the reliability of electronic devices, particularly in 3D package devices. YINCAE Advanced Materials, LLC has developed a novel high thermal conductive underfill for flip chip applications. Diamond powder is selected as filler in our product system due to its excellent thermal stability and high thermal conductivity. Three different diamond powders have been used as filler in underfill, the thermal conductivity has been increased many times (up to 6w/mk), which can greatly reduce the thermal stress for solder joint. The flowability, pressure cooking test and other properties of underfill have been characterized and investigated. All details will be discussed in this paper.

More and more Land Grid Array (LGA) components are being used in electronic devices such as smartphones, tablets and computers. In order to enhance LGA mechanical strength and reliability, capillary flow underfill is used to improve reliability. However, due to the small gap, it is difficult for capillary underfill to flow into the LGA at SMT level. Due to cost considerations, there are usually no pre-heating underfill or cleaning flux residue processes at the SMT assembly line. YINCAE solder joint encapsulant SMT 256 has been successfully used with solder paste for LGA assembly. Solder joint encapsulant is used in in-line LGA soldering process with enhanced reliability. It eliminates the underfilling process and provides excellent reworkability. The shear strength of solder joint is stronger than that of underfilled components. The thermal cycling performance using solder joint encapsulant is much better than that using underfill. Bottom IC of POP has been studied for further understanding of LGA assembly process parameters. All details such as assembly process, drop test and thermal cycling test will be discussed in the full paper.

With the increasing demand of device miniaturization, high speed, more memory, more function, low cost, and more flexibility in device design and manufacturing chain, YINCAE has published a white paper on a first individual solder joint encapsulant which can eliminate underfilling process with at least five times solder joint increase and provide more flexibility for fine pitch and high density application. In order to meet the demand of manufacturing of high speed and low cost, YINCAE has invented a room temperature stable and jettable solder joint encapsulant adhesive – SMT 266. The invention of SMT 266 has allowed our customers to have more flexibility in their high-speed production line such as worry free on the work life of adhesive and workable jetting process. After being used in the customer field for a few years, the implementation of SMT266 has been approved improving the process yield, eliminating voids and cracks in solder joint, eliminating head-in-pillow issue for large component during lead free reflow process. The results from thermal cycling test indicated that the first failure cycles using SMT266 is high up to 6000 cycles, at least 4000 – 5000 cycles higher than other processes. The pull strength is 1.5 times higher than using solder paste plus underfilling process. All reliability data implied encapsulating each individual solder joint is the right direction to move toward. The enforcement mechanism will be discussed in our paper.

In order to meet the demand of fine pitch and 3D package, and eliminate complex underfilling process, a first solder joint encapsulant has been invented. Solder joint encapsulant adhesive is to encapsulate each individual solder joint using polymer to enhance solder joint, and leave empty space in-between solder joints to avoid thermal stress applied onto solder joints. Now two kinds of solder joint encapsulants are SMT256 and SMT266, which have been used in the customer field. Using solder joint encapsulants – SMT256 and SMT266, the pull strength of solder joint has been increased by about five times, resulting in significant increase in the reliability. In this paper more details have been investigated.