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Package-on-Package Process; an interview with Jim Hisert

Package-on-Package (PoP) use in the SMT process is slowly creeping from a niche application into mainstream use. From experience, I know that some customers are using off-the-shelf Wireless Local Area Network (WLAN) and Bluetooth Personal Area Network (PAN) integrated into their current PCB designs. Systems that already exist suddenly become user friendly with the addition of easy Bluetooth, such as portable navigation systems or even my new motorcycle helmet. So, with that, I'd like to try something different, and post an interview with our Semiconductor Application Engineer, Jim Hisert, and resident Package-on-Package expert. Jim, what is the biggest issue facing the widespread use of PoP's in the world today? Well, Mario, it is a different process. I would say component dipping is "easier" than standard SMT into solder paste, because customers are just so accustomed to paste printing. There is also a limited material set and knowledge base for this process, so I find many people feel they are pioneering and become uncomfortable. We try to provide as much knowledge as we can up-front to shorten the learning curve. Lets talk about the component dipping process. Can you diagram the process of PoP use in the SMT world? There are actually two different process sequences that are mainstream. Process "A" -Stencil print solder paste on the entire board (this will be used for all standard SMT components and the bottom component in the PoP stack). -Place standard SMT and bottom PoP components. -Dip second level PoP component in PoP solder paste or flux. -Place second PoP component on top of bottom PoP component. -Repeat if necessary for +2 level component stacks. -Reflow. Process "B" -Stencil print solder paste on the entire board. -Place a pre-assembled PoP stack along with standard SMT components (They can be purchased pre-assembled by the manufacturer in some cases, although this limits the modular application flexibility of separate PoP components). -Reflow. Based on your experience, what can we do to help existing and theoretical processes? There are so many things to do! We need to evaluate existing materials, new materials, and competitor materials. We should keep track of new process developments and possible issues to share with our customers to make their life easier. It is important to help customers select materials, and then be there on the line to help set up the process and get the equipment settings dialed in. I feel that many customers take too much on by themselves; why "re-create the wheel"? Thank you to Jim Hisert, Semiconductor Application Engineer for Indium Corporation. More information may be found at Jim's Semiconductor Blog or Online Help: Indium Knowledge Base.