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The world of electronics has come far from what we used to see back in 1900. This advancement is due to the use of multi-chip modules on PCB assemblies. Multi-Chip Modules allow designers to integrate ICs, components, and conductor dies into a single substrate. This allows for a compact solution while making sure the performance is optimum.
In this blog, ELEPCB will introduce multi-chip modules, their benefits, the types available, and crucial information that will help you understand these smart integrated circuits.
What is Multi Chip Module on PCB?
Multi-chip module aka microchip module is an electronic assembly that contains a series of components, integrated circuits, traces, and dies all together. This gives Multi Chip Module the structure of a complete package that has pins and terminals. When completed, an Multi Chip Module can be used as a big IC and can be soldered to the PCB.
Multi Chip Module packages come in a variety of shapes and packages that range from pre-packaged ICs to footprints of already manufactured chip packages. These custom-made packages are used in a variety of electronics where size and weight are limitations.
Some of the common applications of MCM includes:
- Smart electronics like laptops, smartwatches, and CPUs
- Radio systems and communication devices
- Medical devices
- Military vehicles and modules
- LEDs
Benefits of MCM Assembly
One of the outstanding advantages of micro-chip modules is that these assemblies allow for the miniaturization of electronic devices, making them more portable and suitable for weight/size-limited applications. Apart from that, here is what these packages can offer.
1. Uses Less Power
- MCM diminishes the need to connect multiple electronics. That is because all the important components are connected inside the assembly. This allows for shorter connection lengths, and since the length is small, the circuit can be powered using low power.
2. Enhanced Reliability
- If we talk about larger chips, they have a high ratio of circuit failure, unlike MCM where the circuits are interconnected using packed connection lines. Due to multiple chips, the interconnection paths are small, hence which leads to lower issues and high reliability.
3. Lower Manufacturing Costs
- Using individual ICs in PCB assemblies can lead to higher production costs. However, when these assemblies are combined in the form of MCM, that lowers the costs, making the large assembly more affordable.
4. Lower Chance of Interference
- Since all the electronic assemblies are packed in a single IC, that allows for small interconnection lines between the components. Since, there are short connection paths that enable circuits to face less interference and more signal integrity.
Explaining the Design of Multi-Chip Module
In order to get an understanding of multi-chip module design, it is important to understand how these small yet powerful chips are designed according to the specifications.
The design of MCM goes through the following steps.
Step 1:
Substrate
Step 2:
Layers of Conductors
The first step towards designing an MCM chip is selecting the substrate type. The substrate is the base material where it houses the components, and wires.
Substrate comes in the categories mentioned above and can be selected according to the design parameters.
Multi-chip modules contain a leveled structure and that structure contains many layers of conductors. The layers are designed according to the type of MCM chip and are made using the electrochemical microfabrication method. This method creates thick layers of conductors that have lateral dimensions.
Step 3:
Packaging
Step 2:
Bonding
After the layers, the MCM is packaged which provides mechanical support, electrical connectivity and thermal management. The packages come in a variety of shapes and technology.
The last step of MCM design is the bonding of the designed chip. Bonding is the method that connects the designed chips into the substrate. Techniques like wire bonding, tape automated bonding, or flip-chip are used for this process.
Types of MCMs Based on Substrate
MCMs are categorized according to the substrate type. The substrate decides which MCM type should be used according to the defined requirements. Here is what you can find in the market.
MCM-D:
D type uses a layer of dielectric that is made of glass, metal, or ceramic substrate. The substrate contains a layer of thin film that connects components in the assembly.
MCM-S:
Another type of MCM is an S-type that is made from silicon substrate. With this type, the tracks and traces are made in the silicon to connect the components.
Types of MCM Packaging
Based on Interconnection Design
MCM packaging types have multiple options available. These packages come in categories such as 2D, 2.5D, and 3D technology.
Redistribution
Layer Fan-Out:
Suitable for applications such as Internet-of-Things, layer fan-out MCM packages have the capability to offer the same density as silicon interposers, but at a lower price. If you are looking for improved performance and more iOS, then these 2.5D packages are the best solution.
Hybrid Bonding:
Hybrid bonding is a 3D package that is created by bonding two wafers together using TSVs (Through-Silicon Vias). This 3D stacked packaging offers the most performance and highest density because this technique lowers power wastage. On the other hand, the hybrid bonding package is expensive when compared to silicon interposers and has more complexity.
Organic Substrate
Organic substrate is the most common type of 2D package that is widely used in the electronic industry due to the fact that it is cost-effective. Moreover, this packaging type is suitable for applications where lower IO density is preferred and the die connections are fewer.
Silicon Interposer
Silicon interposer is a 2D MCM packaging type that leverages silicon interposer to connect two dies together.
Inspection of MCM Modules and Assembly
MCM are important components that are helping electronics get on the path of modernization. Below are some of the methods that are used for inspection and testing.
Inspection
There are two ways through which you can inspect the MCM chip.
- Manual inspection
- Machined inspection
With manual inspection, the designer uses magnifying glass, and digital multimeter (DMM) to check the break, bond integrity, and substrate integrity. With this, they can also find the cracks between dies and solder quality.
The second method is machined inspection.The machines leverage ultrasonic waves to detect the spaces between and penetrate metallic elements. The machines can detect faults that include solder bond integrity, cracks in die, excessive/insufficient solder material, substrate integrity, and lid seal cracks. Apart from that, 2D/3D X-ray machines can also be used to inspect and troubleshoot problems in MCM chips.
PCB Multi Chip Module Standard
Joint Test Action Group (JTAG)
The first method is leveraging the bound scanning method. With use of Joint Test Action Group (JTAG), the designers can detect whether the chips are interconnected without needing to use any probes.
JTAG standard is 1990, by the IEEE (Institute of Electrical and Electronics Engineers) developed, also known as “IEEE 1149.1 standard”.
The content of the standard includes three main parts:
- Boundary-scan testing
- This is one of the core functions of JTAG. In the design of integrated circuit chips, boundary-scan units are integrated around the input/output (I/O) pins of the chip. Through the JTAG interface, these boundary-scan units can be controlled to realize the test of inter-chip connections.
- For example, if a printed circuit board (PCB) has more than one chip, the use of JTAG can be in the case of not using physical probes to contact each chip pin, to detect whether the connection between the chip is correctly connected, whether there is an open or short-circuit condition.
- Device Programming
- JTAG interface can also be used to program the chip.
- For example, in Field Programmable Gate Array (FPGA), configuration data can be written to the chip through the JTAG interface to redefine the function of the FPGA.
- In-System Debugging
- For some complex chip systems, JTAG provides a means of debugging in the system running state. JTAG interface can be used to access the chip’s internal registers, view the internal signal status, etc., which helps to find errors in system operation.
Testing
In-Circuit Testing is a method that involves probes and nail-beds.
It allows testing of single components.
If you want to know more about ICT Test in PCB, check this out!
Conclusion
The electronics are getting smarter and more portable because their PCB boards are getting smaller. The ICs attached with the PCBs are getting reduced in size and more intelligent. All this was made possible through Multi Chip Module, making them compact, affordable hence increasing demands day by day.
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