UCIe (Universal Chiplet Interconnect Express)

UCIe is an open standard for connecting chip to chip. It links several chip pieces, called dies, inside one package. If many companies follow the same specification, pieces from different manufacturers can be combined.

If you make a high-performance chip as one large piece, more of them come out defective, so yield falls and cost rises. As a result, more chips are now built by making small pieces separately and joining them, and the need for a common specification between the pieces has grown.

UCIe sets the standard from the physical connection that sends the signals to the rules for exchanging data, so that communication between pieces matches. In 2.5D, pieces sit side by side on a substrate, and in 3D they are stacked up and down and connected over a short distance.

A connection channel is divided into several lanes that send data in parallel. You calculate bandwidth by multiplying the number of lanes by the transfer speed, and you compare performance by how much is sent per unit of time.

It is used when a high-performance AI accelerator or server chip is designed in several pieces. In a structure where you choose and attach memory, input and output circuits and compute pieces, it helps match the connection specification.

A designer must first decide whether to use a 2.5D or a 3D package and what the bandwidth and power budgets are. If the conditions do not fit, the expected performance will not appear even with the standard.

Following UCIe does not solve every connection problem. Package design, heat management and signal integrity verification are still needed.

It is easy to judge performance by the name of a standard, but real speed depends on the implementation and the package conditions. Even with an open specification, not every manufacturer implements it to the same level.

It is like building blocks made by different companies that still snap together as long as the studs follow the same specification. When the specification is the same, you can pick pieces and assemble them.

In an age when several companies make the pieces of a chip, the connection specification is what decides compatibility. Knowing UCIe helps you see why the way pieces are joined matters in articles about chip design.