definition, types and uses in MCM configurations

Interposers usually are not a novelty, however a lot of the analysis and growth of NVIDIA, AMD, Intel or different firms in the sector have gone in this path in current years, since in the identical means as the event of chiplet-based architectures is necessary, so is your intercom.

What is an interposer?

MXM Interposer

Technically an interposer is a kind of PCB, so it’s a board on which a number of chips are mounted on high of it. Interposers are historically so known as resulting from the truth that they’re a plate that’s positioned between what’s the foremost PCB and the chips that go on high of it. For instance an MXM module in which the devoted GPUs for laptops are mounted will be thought of interposers.

This can be the case of some chips with exterior “embedded” reminiscence, such because the L4 for the Intel Iris that got here out a couple of years in the past, the place each the embedded reminiscence and the SoC had been mounted on the identical interposer.


But, in current years using interposers has been associated to what are known as 2.5D IC built-in circuits, that are primarily based on the implementation of a 3D DRAM reminiscence, normally HBM and subsequently use vertical interconnections. These interposers are designed to supply communication as quick as attainable with the bottom attainable vitality consumption, and if there’s something that provides HBM reminiscence a bonus over different reminiscences corresponding to GDDR6, it’s its pJ / bit ratio.

Simply in case you do the calculation of multiplying the pJ / bit by the bandwidth per second, in bits, it is possible for you to to see the consumption and how the HBM2 is a reminiscence with a better efficiency for consumption. However, a lot of the magic is because of the interposer that communicates the totally different components, which is crucial in the development of a 2.5DIC system

Moving knowledge is dear

Data Movement

If you ask any professional in the sector who has been designing new architectures then you will note how the reply will at all times be the identical. The drawback is not in getting as many calculations as attainable, however in getting as a lot knowledge motion as attainable inside a hard and fast vitality funds.

All the chips have a sequence of knowledge pins that serve to ship and obtain data between them, every sending of knowledge has an vitality price, which to extend the bandwidth requires two customary options:

  • Increase the variety of pins, which ends up in the rise in the scale of the chip, that is much less chips per wafer and the discount of the obtainable inventory. Apart from creating extra latency issues because of the bigger dimension.
  • Increasing the clock pace of the exterior interfaces is just not a rise in value, however quite in consumption, since consumption will increase quadratically with the clock pace and this will increase linearly with the voltage.

CPU socket

The resolution that was reached was to put the pins vertically, in such a means that there will be many extra with out rising the realm of ​​the chip. The thought is similar as what we will see in CPU sockets the place we’ve got a whole bunch of pins that talk with the board. The thought with the interposers in 2.5DIC configurations they convey vertically with all of the chips and then the interposer itself is in cost of transferring this knowledge.

So we’re speaking about numerous interconnections that should be carried out by the interposer, which implies that it has to have monumental inner complexity and that these are completely vital in these configurations.

Types of Interposers

CoWoS 6th Gen

There are totally different types of interposers, of which we’re going to speak subsequent, not mentioning particular manufacturers or proprietary applied sciences, however quite giving a basic clarification of the totally different types of interposers that exist. However, it should be clarified that each one of them are designed for the implementation of two.5DIC methods.

Silicon interposers

AMD Radeon Vega Graphics

They are probably the most used and in the intervening time the one ones that exist in the large-scale business, for all the pictures that accompany this submit are of this kind of interposers.

They are known as like that resulting from the truth that they’re nonetheless one other chip, however on a big scale. The drawback? They are costly to fabricate and can vary in price from $ 30 to $ 100. In addition, they’ve the issue that they can’t supply clock speeds for communication past four GHz. Since HBM reminiscence requires much less clock pace in the intervening time, it has not reached its restrict.

Organic Interposers

Organic interposers

They are these which are normally used in their development natural parts corresponding to epoxy resin. They wouldn’t have the identical efficiency as a standard silicon interposer, because it permits a lot decrease clock speeds, however their price of manufacturing may be very low and is between 2 and three {dollars}.

The motive why they can’t attain the clock speeds of silicon interposers is principally resulting from the truth that they can’t tolerate excessive temperatures, so this determines the design of the interfaces which are created on them, in addition to their use.

Organic interposers don’t use silicon pathways for intercommunication, however there are so-called 2.1D interposers which are a mix of silicon and natural interposers, the place the excessive switch pace of silicon at a decrease pace is sought. price.

Glass Optical Interposers

Crystal interposers

There are additionally interposers fabricated from glass, these usually are not primarily based on communication utilizing electrons, however quite they convey by photons. They are subsequently those with the best efficiency, however their manufacture is advanced. Most probably, they may find yourself changing the silicon interposers when vital.

Being in a position to talk by optical intercom eliminates the necessity to run tracks by means of silicon by means of the interposer. So it’s a totally different paradigm, which we’re going to take years to see.

We additionally should take note of that they may want a brand new kind of producing, since we aren’t speaking about the identical methodology to fabricate them as silicon and natural interposers. This can restrict its availability to high-performance tools corresponding to servers and supercomputers for years.

Silicon bridges or interposers with out TSV

EMIB Intel Interposers

The bridges are silicon interposers, however with a particularity, they don’t use pathways by means of silicon. This resolution will develop into well-known in a couple of years, since it’s the type of intercommunication chosen by Intel with its EMIB and a variant of it’s specified in the patents of future methods primarily based on AMD chiplets, so they’re turning into the best various to silicon interposers for the home market.

The thought of ​​bridges is to straight join the chips as an alternative of getting an inner interconnection. It is a perfect resolution for when there are few chips on high of the interposer and with a a lot decrease price.