Guide

Embedded PCB: A Comprehensive Guide for Beginners

Embedded PCB Stackup

A few decades ago we saw that computers were too big to fill a room. Technology has evolved from a mega size to a much smaller form factor. Evolution of technology vacuum tubes were replaced by transistors. Transistors were replaced by silicon chips and created a milestone in the electronic industry.

With today’s technological development, we are using small electronic devices that are compact in hand. We see many small electronic devices in the market now and we buy and use them.

Vacuum tubes to transistors to ICs

Vacuum tubes to transistors to ICs

Why Embedded PCB Come into Being?

Especially when manufacturing small electronic devices, PCB is forced to be small. Designers use a large number of components to make those devices work. It’s a complex situation when the PCB size is small and the components are many, for such cases, designers moved to Embedded PCB.

Let’s take a look at EMBEDDED PCB Advantages,

  • Embedded PCB (Miniaturization of PCB)
  • Replacement of package
  • Providing space for components on Outer layers
  • Integrated shielding
  • Short signal paths
  • Protection against plagiarism
  • Reliability
  • Thermal management
  • Mechanical stability

What is Embedded PCB and the Main Advantages

Let’s discuss what’s embedded PCB and how it helps to miniaturize electronic devices.

Embedded PCB is a method of converting a large and multi-component design into a smaller one. Based on the application, PCB can be made from a single layer to multiple layers. But components can be placed either through-hole or SMD only on outer layers for normal PCBs.

Through-hole components

Through-hole components

For Embedded PCB, PCB is adapted to place components to the inner core of the PCB. Which helps reduce track distance and increase the reliability of the connection. And also creates space for components on the outer layer of the PCB.

Embedded resistor, capacitor or inductor in PCB

Embedded resistor, capacitor or inductor in PCB

Techniques of Embedded Components in PCB

Where components like resistors, inductors, capacitors and IC chips are embedded in the stack up which call it as active and passive embedded components. It’s not limited to placing components between stack up and also fabricating passive components like resistor inductor and capacitor while designing PCB between stack up.

  • Forming Technique
  • Placement of components on the inner core

Forming Technique:

It’s an advanced technique of forming/fabricating resistors, inductors and capacitors during manufacture of PCB. During this method components are not placed, but it is creating/fabricating components on the inner core of the PCBs.

In this method, resistors and capacitors can be fabricated or moulded at higher efforts, its easy to understand and fabricate the inductor. Because Inductor coils can be designed to all layers and etched like normal tracks.

The below image shows inductor coil fabrication during PCB manufacturing.

Coil fabrication during PCB manufacturing

Coil fabrication during PCB manufacturing

Placement of Component:

In this method, discrete components like resistors, inductors, diodes and capacitors are directly available. Which will be placed in the inner core like the surface mount technique. Once components are placed, they will be covered by prepreg, followed by core or copper foil and stacked again.

Components placed in the inner core

Components placed in the inner core

Embedded Component Placement Methods

Active and passive embedded components can be done by creating a cavity or covering components with prepreg after placement of the resistor, inductor or IC.

When components are quite smaller we can cover and make connections using laser technique and can make direct connections from the top layer.

When components are big they have to create an opening or clearance to assemble the component from the outer side. While talking about big components, ICs are big when compared to passive components. IC can be placed on the inner core by the following two methods:

  • Face up component placement
  • Face down component placement

Based on how the IC chip is placed it is said to be Face up or face down. Simply IC’s terminal (soldering side) is facing the top layer or bottom layer.

Face up component placement

Face up component placement

Face down component placement

Face down component placement

Cons of Embedded active and passive components:

  • Need more skill and time
  • Components cannot be easily replaceable
  • Higher Cost

Introduction of Embedded Coin PCB

In PCB thermal management is important for high current and high voltage PCB boards. PCB while working components like IC may overheat during its high performance. While absence of cooling techniques or thermal management may lead to the failure of components or may reduce the performance of PCB.

In the design stage designers should be aware of all heat dissipation methods to overcome all chances of failure of components, reducing performance.

Common heat dissipation methods used in PCB at the design stage are,

  • Thermal pad
  • Heat sink
  • Thermal via
  • Solid copper
  • Metal back PCBs
  • Aluminum back PCB

We can use the above four methods separately or a combination of all methods is also possible.

Common heat dissipation methods used in PCB at the assembly stage are,

  • Thermal paste
  • Cooling fans

The above two methods can commonly seen in CPU and SMPS.

Embedded Coin PCB Applications

As said before high current and high voltage equipment,

  • Automobile
  • Telecommunications
  • Industrial
  • Military
  • Medical equipment

Why Use Copper in Embedded Coin PCB

Especially we are using copper for this technique.

Copper has extraordinary properties at an affordable cost while gold and silver could cost more when compared to copper. Copper is an excellent conductor which also transmits heat rapidly to the surrounding environment using a heat sink or solid copper. Copper also has good properties of corrosion resistance.

Copper thermal pads for SMD components can seen be under QFP (Quad Flat Package) commonly to transfer heat from QFP integrated circuit. And through hole thermal pad with airgap helps to dissipate heat using atmospheric air.

Types of Embedded Coin PCB

  1. Buried copper coin
  2. Embedded copper coin

Buried copper coin:

The term itself buried, means solid copper which is placed in the middle of the core and cannot be seen from the top or bottom layer.

Cross-sectional view of buried copper coin

Cross-sectional view of buried copper coin

3-D view of buried copper coin

3-D view of buried copper coin

Embedded copper coin:

Solid copper placed from the top/bottom layer to the inner layer. It’s like embedding or inserting or pressing coin-based copper structure or shape on the PCB either buried or through (top to bottom).

Cross-sectional view of embedded copper coin

Cross-sectional view of embedded copper coin

3-D VIEW of embedded copper coin through PCB

3-D VIEW of embedded copper coin through PCB

Shapes of Embedded Coin PCB

Embedded coin can have shapes such as:

  • U-Coin
  • I-Coin
  • T-Coin

U-Coin:

U shape can be achieved by cavity process, which helps to place components into the cavity and helps to dissipate heat.

U-Coin embedded coin

I-Coin:

I-Shape PCB coin thermal via’s present and those thermal via’s filled with resin fill like the below image to dissipate heat from component to surface.

I-Coin embedded coin

T-Coin:

This shape is flat especially helps to solder SMD components on the surface of the PCB and helps to dissipate heat.

Conclusions:

Embedded PCBs are more and more widely used in high-tech electronic devices. Embedded PCB techniques do have some flaws which could be resolved in upcoming days and make way to miniaturize electronic devices.

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