How a smartphone soc is made?

Smartphones have become part and parcel of our life. An average person spends 5.4 hours a day on their phone, and 44.81% of the world's population owns a smartphone. Modern-day communication is based mostly on smartphones. It need not be mentioned that streaming platforms have become a major part of entertainment nowadays. All these things are made possible by an extremely complex piece of hardware inside every smartphone, called SoC. Which is similar to the processor of any laptop or a desktop computer. Let’s go to the journey of how the SoCs are made?

Where the SoCs are kept?

  System on a chip is a complete system of related computing hardware that is used for different tasks of a smartphone, a detailed description can be found here. Every component in any computing platform is created through a set of extremely complex processes. That not only require time to build but also takes lots of investments. Let’s take an example to make things easier to understand.

The below picture is a torn down apple iPad-2, 

Torn down apple iPad-2 credits: Computer organization and design, by David A. Patterson & John L. Hennessy

typically we can see the following things there:

1.            At the top is the capacitive multitouch screen and LCD.

2.            To the far right is the 3.8 V, 25 watt-hour, polymer battery, which consists of three Li-ion cell cases

3.            The metal back of the iPad (with the reversed Apple logo in the middle) is in the center

4.            In the center, is we think of as the mainboard for SoC; they are often L-shaped

If we pay attention to the L-shaped board there, we can see the large integrated circuit in the middle, is the Apple A5 chip, the SoC package. 

Apple A5 circuit board, credits: computer organization and design, by David A. Patterson & John L. Hennessy

And after tearing down the IC packaging we can see the most important things of concern, the SoC itself.

Apple A5 SoC, credits: computer organization and design, by David A. Patterson & John L. Hennessy

Believe it or not, this a few mm square chip consists of billions of transistors, which are the basic building blocks of any computing device. Today’s transistors are 3d transistors, sometimes they can be CMOS transistors or sometimes FinFET, the new candidate, which fab lab like Intel or Samsung uses. A typical example of a transistor may look like this, 

FinFET, credits: researchgate.com

and its length is nearly 10 to 20 nano metes.  

How a transistor is created?

1.        The journey starts from ‘sand’, you heard is right. Sand contains silica, which is the source of silicon, the most important ingredient of a transistor. Silicon is one of the components by which a transistor is created, there are others like germanium, etc. Due to several useful properties, Si is used in fab labs. 

2.        Sand is heated adequately so that by some chemical reaction, a long cylinder (called ingot) of pure silicon is formed. This silicon cylinder needs to be 99.99% pure, a minute amount of impurity level could hamper its ‘semiconducting’ property, and thus cannot be used in a transistor. Then from the cylinder circular wafer is cut precisely where the final circuitry (SoC) will be inscribed.

3.        On the other, a team of brilliant engineers creates the blueprint of an efficient and highly optimized in the power-performance-area circuit (SoC, for example in this case apple A5). The circuit is rigorously tested in different conditions and when found to be according to the specification set, engineers shared the blueprint of the circuit with the fabrication company where the silicon wafer (mentioned in step 2) is created.

Physical Circuit implementation of an SoC circuit (not A5) , credit: Wikipedia, under GNU license 

4.        In the meantime, the 99.99% pure silicon wafer is tested for conductivity, purity, etc. and the wafer passes the test are chosen for fabrication. Then the wafer is cut into several small rectangular pieces, each piece will have an SoC circuit inscribed in it shortly.

Silicon wafer to small dice transformation, credit: Peellden & Nick Knupffer 

5.        As the lab has the complete blueprint of the SoC, they prepare a suitable ‘mask’ to carefully make a copy of the SoC circuit. During the process, UV-light is used extensively, which is used to inscribe the mask pattern on to the Silicon rectangular dices. That’s why sometimes it is called the photo-lithographic process. This step is the most crucial, complex step and consists of several other sub-steps, which have been skipped for simplicity.

To inscribe the circuit onto Silicon, these kinds of a mask is used to control UV light exposure, credits: Shigeru23

6.        Once the SoC circuit is inscribed on to the Si wafer, each one of them is sent for automated testing so that its functionality can be verified. In this step, many chips cannot pass and only a percentage of fabricated chips are actually sent to the next step.

7.        In this step, metal wires are soldered with the tested Silicon dice and covered with an appropriate package. The packages are usually black colored that we see on any circuit board. In our case, the package is labeled as ‘A5’, which has been shown at the beginning. At this stage, the SoC chip leaves the fabrication facility and starts its journey towards the circuit board integration department.

First wire is attached with SoC & then packed into a black package, credits: Mister rf 

Conclusion:

We have seen where an SoC is kept inside any smartphone or tablet. We have gone through how a smartphone SoC is made? We have explored several steps of fabrication for the same. The steps mentioned here are extremely complex and not usually done by a single manufacturing company. Step 3 is usually done by a separate group of people and requires months of cumulative efforts. That’s why the whole procedure is extremely costly and is not suitable for a single unit of a manufactured chip. The entire cost of production is distributed among millions of chips so that any individual can pay according to their budget. I hope that clarifies how an SoC is made?