Unpackaged Die In Embedded Designs Have Benefits.
Embedded system designers have benefitted from procuring integrated circuits (ICs)
such as microcontroller (MCUs) in die form for many years. Because the dimensions
of die are much smaller than when the IC is packaged, the use of unpackaged die allows
the product designer to significantly reduce the size of the electronic circuit.
High-volume products such as hearing aids, cell phones and RFID cards have become more comfortable, more portable and thinner due to the integration of die in the circuit design. Until recently, lower volume products have not benefitted from the same level of innovation as it has been historically difficult to procure reasonably priced die in low volumes.
The benefits of using unpackaged die in embedded designs can be substantial. The availability of IC products in die form gives customers a convenient option for small-footprint designs, enabling them to optimize their product designs for limited space and to implement innovative, proprietary packaging solutions.
There are additional benefits of using die in system designs rather than packaged ICs. Because the electronic circuit is contained in a smaller space, the length of the interconnections between the chips is reduced, which in turn reduces the effects of capacitance and inductance and thus minimizes the switching latency. Electrical noise is also minimized, which is particularly beneficial if there are radio frequency signals in the system.
Die utilization can be particularly effective for sensor-based products. MCUs often include an integrated on-chip temperature sensor that exploits the known characteristics of a bipolar junction transistor to make an accurate temperature measurement. This integrated sensing technology can be useful for temperature compensation effects when, for example, implementing a temperature-compensated real-time clock. When there is an IC package around the die, additional thermal resistance is introduced into the system. A more accurate temperature measurement can be achieved when there is no package on the die.
Several technologies have emerged to accommodate the integration of unpackaged die in an embedded system. Multi-chip modules (MCM) have become quite popular in many product implementations. Variations on this theme also include multi-chip packages (MCP) and system-in-packages (SIP).
Numerous assembly house vendors can accept wafers, dice them and place them in these package types. Custom packages often are developed that take a mechatronics approach to optimizing both the electrical and mechanical properties of the system to provide a tiny footprint solution. A prime end-product example of this approach is a state-of-the-art hearing aid, which requires a very space-efficient design and high levels of circuit integration.
Product designers should consider using die if this approach will bring tangible benefits to an end product, such as shrinking form factors, reducing weight and making the product more ergonomically appealing to consumers. Close consideration should be given to the manufacturing technology.
There are a couple of common technologies used with die implementations today. For example, chip-on-board technology enables the die to be mounted on a substrate and electrically connected using conventional wire-attach techniques. The die is sometimes encapsulated to protect the fragile silicon during the manufacturing process.
Flip-chip technology is more elegant but requires some additional processing steps to the wafer to add solder balls underneath the die. The resulting implementation can be smaller and more robust but also more expensive to manufacture.
The Good News
The good news for embedded developers is that all of the appropriate wafer handling technologies, IC products in die form and services are now becoming more commonplace and affordable. The availability of fully tested die in wafer form is enabling the development of innovative, tiny mechatronics devices that might not have been feasible using conventional packaged semiconductor products.
Reference: Electronics Weekly