is the optimal ASIC implementation in one sense. It gives the best technical possibilities, the smallest possible die size and the lowest part price. The time, cost and risk to develop the ASIC is however higher. A full custom circuit shall therefore normally be considered when the annual production volume is planned to be relatively high or when technical limitations prevent from using other solutions.
SGA normally works with full custom processes suited for analog and similar to the processes used for our arrays. The full custom processes may however have additional options like CMOS for efficient implementation of digital functions and DMOS for handling high voltage and/or current. The full custom approach also makes it possible to achieve optimised solutions for very tricky analog performance requirements that can not be achieved using an array.
Processes available include options like:
· 2 to 90 volt bipolar for precision or high voltage analog
· 2 to 15 volt CMOS or BiCMOS for analog, digital and mixed signal
· N- and P-DMOS options for high voltage and/or current
· Ion implanted, poly and/or thin film resistors
· Precision and high value capacitor options
· Dielectric isolation for temperatures up to 225 °C
Two step solution
When it is judged that the time to market is important or the risk for an iteration of the ASIC is high, it is also possible to first develop an array for a later conversion to full custom for really high volume applications. The array based circuit can be used for market introduction and during ramp up of production and the full custom will later reduce the production cost even further.
Multi Project Wafer
Some silicon foundries offer a MPW (Multi Project Wafer) option. This means that several customer projects share the same silicon and therefore also the costs for masks and prototype manufacturing. This is an option that can be used to reduce the initial cost and risk for a full custom development project to a level similar to arrays. The full costs for the custom specific masks will then be needed only when the volume production starts. SGA normally use this option when available and when the timeplan for a project can afford the added leadtime.
Design libraries and manuals are available and are similar to the library used for the SLA arrays. The flexibility when developing a full custom ASIC however makes it harder to fully utilize all benefits without deep knowledge in the processes, so SGA is normally much more involved in the design phase for a typical full custom development project compared to a typical array project. A typical full custom project is therefore normally developed turn-key by SGA.
Quality and package options
Full custom circuits can of course, like the arrays, be delivered in different quality levels and in most types of packages available on the market including delivery as bare Die.