As consumers demand smaller memory chips with greater capacity, engineers optimize the manufacturing process to ensure the chips will hold up.
The following is an excerpt from Multiphysics Simulation 2017.
By: Lexi Carver
In the 1980s, during the dawn of what would become a booming tech industry, flash memory made a splash by offering erasable and programmable computer storage. These storage chips now appear in cameras, memory cards, USB sticks, and phones that can store thousands of photo, music, and video files.
Though they often go unnoticed by consumers, designers work tirelessly to keep up with demands for smaller size and greater capacity. Behind the production of a single memory device stands a long line of researchers, engineers, and assemblers who must overcome the manufacturing challenges associated with processing these tiny chips.
KEEPING THE DIES INTACT
Memory chips are produced by placing a 300 mm diameter semiconductor wafer onto a carrier tape, then separating the wafer into single chips. Once removed, the tape leaves behind a thermoplastic adhesive on the chip undersides, later enabling bonding to a substrate using heat and compression. Chips are bonded into stacks to increase the amount of memory in a given area. Wire bonds connect the chips and the substrate. Finally, an entire sheet of stacks is put into a molding machine, encased in protective plastic, and then separated into many pieces, each containing a stack of memory chips (Figure 1).
Figure 1. Top left: Dies being bonded onto a substrate before being wire bonded, coated in the plastic mold, and separated. Center: Stacks of dies on a substrate. Right: Back of the substrate showing the interfaces for connecting the memory chips to larger devices.
But removing the tape without bending the thin dies too much poses a tricky problem. With thicker chips from decades past, manufacturers used a multi-needle ejector to remove the tape using a series of pins. But these place too much stress on the thinner dies; the multi-needle ejector runs the risk of wrecking them.
As chips got thinner eight or ten years ago, we were shocked at how many dies broke, says Stefan Behler, senior expert process engineer at Besi Switzerland AG. We needed a new way of peeling off the tape that...