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Electronic manufacturing industry PCB/PCBA knowledge
package substrate - A comprehensive exploration

The package substrate provides electrical connection between the chip and different circuits of the conventional PCB, and provides protection, support, heat dissipation channels for the chip, and achieves the effect of meeting the standard installation size. With the development of technology, semiconductor package substrates in the form of BGA, CSP and flip-chip (FC) have rapidly expanded their application fields in recent years.

This article will take you to explore the package substrate in detail, understand what package substrate is, what role it plays in IC package, and what are the main package substrate technologies.

Table of Contents

What is package substrate

What is package substrate
What is package substrate

Package substrate is composed of electronic circuit carrier (substrate material) and copper electrical interconnection structure (such as electronic circuit, PCB via, etc.), in which the quality of electrical interconnection structure directly affects the stability of integrated circuit signal transmission and reliability determine the normal performance of electronic product design functions. The package substrate belongs to a special printed circuit board, which is a basic component that connects a higher-precision chip or device with a lower-precision printed circuit board.

The package substrate can be simply understood as a PCB or thin-thick film circuit substrate with higher performance or special functions. It has outstanding advantages such as realizing multi-pin, reducing the area of packaged products, improving electrical performance and heat dissipation, and achieving high density.

What is the function of package substrate

1. The package substrate acts as a carrier structure to protect the semiconductor components in the chip;
2. Realize the electrical connection between the electronic circuit of the integrated circuit functional module in the chip and the external functional components;
3. Provide supports and heat dissipation channels for chip functional components;
4. Provide an assembly platform for other electronic components.

In addition, the package substrate can achieve the purposes of multi-pin integrated circuits, reduced volume of packaged products, improved electrical performance and heat dissipation, ultra-high density or multi-chip modularization.

What are the different types of package substrate

What are the different types of package substrate
What are the different types of package substrate

Mainstream package substrate classification:

1. Classified by substrate material

  • Rigid organic package substrates
  • Flexible package substrates
  • Ceramic package substrates

2. Classified according to the flexibility of the base material

  • Rigid organic packaging substrate – The general process (single-sided, double-sided, multi-layer board) and the multi-layer PCB of the build-up method are mostly used in BGA packaging products
    Rigid CSP / PBGA / FC-PGA / FC-PBGA / Cavity PBGA
  • Flexible Packaging Substrate – The substrates based on polyimide film, such as BGA, D2BGA, T-BGA, T-CSP, μCSP, etc., are growing rapidly; FilmCSP/Tape-BGA
  • Ceramic package substrate – Alumina, aluminum nitride substrates, low temperature co-fired ceramic multilayer package substrates; Ceramic PGA / BGA / CSP

3.  Classified by manufacturing process

  • Rigid substrates (including ceramic substrates)
  • Flexible substrates
  • Build-up multilayer substrates (BUM)

4. Classified by performance

  • Low expansion coefficient (a) packaging substrates
  • High glass transition temperature (Tg) packaging substrates
  • High elastic modulus packaging substrates
  • High heat dissipation packaging substrates
  • Embedded component packaging substrates.

5. Classified by application field

  • Memory chip packaging substrate (eMMC)
    Storage modules, solid state drives, etc. for smartphones
  • Micro-Electro-Mechanical System Package Substrates (MEMS)
  • Radio frequency module packaging substrate (RF) -or mobile communication products such as smartphones
  • Processor chip package substrate (WB-CSP and FC-CSP) – for smartphones, tablets, etc.
  • High-speed communication package substrate – for data broadband, telecommunications, FTTX, data centers, security monitoring and smart grids
package substrate

Package substrate and IC package

Traditional semiconductor packaging uses a lead frame as the IC conduction line and the carrier supporting the IC. With the development of semiconductor packaging technology, the number of pins has increased (more than 300 pins), and new semiconductor packaging forms represented by BGA and CSP have come out, and a new carrier necessary for semiconductor chip packaging – IC package substrate.

Chip package technology classification

There are many types of chip packaging. In order to facilitate understanding, we simplify the classification method. According to the different shares of consumables used in the packaging process to carry wafers or chips, semiconductor packaging technology can be divided into lead frame packaging, bare chip packaging/wafer There are three types of level packaging and embedded packaging.

1. Lead frame + package case
We classify the encapsulation technology using the traditional encapsulation shell and the encapsulation technology using the encapsulation substrate into one category, collectively referred to as the encapsulation technology using the encapsulation shell in the encapsulation.

2. Embedded Package – Substrate based package
Embedded Component Packaging (EPC) uses a multi-step manufacturing process to embed components into substrates.

3. Bare chip packaging assembly technology/wafer level packaging (WLP)
The introduction of bare chip packaging can reduce the extra volume generated by the package shell, and directly replace the standard semiconductor package chip with an unpackaged bare chip, allowing developers to directly obtain the theoretical minimum size of the chip, thereby improving PCB board wiring space utilization.

4. Lead frame Packages
The packaging technology using traditional lead frame and package shell is called lead frame packaging technology, which is mostly used in quad flat no-lead package (QFN) and quad flat package (QFP ).

What are the differences between package substrate and PCB

What are the differences between package substrate and PCB
What are the differences between package substrate and PCB
Packaging substrates can be simply understood as PCB or thin-thick film circuit substrates with higher performance or special functions.

PWBs and PCBs

PWB (printed wiring board): generally refers to an insulating substrate with conductor patterns arranged on the surface and inside. The PWB itself is a semi-finished product and functions as a substrate for carrying electronic components . Through conductor wiring, it is connected to form a unit electronic circuit and exert its circuit function.

PCB (printed ciruid board) refers to the entire substrate of the PWB equipped with electronic components as a printed circuit board.

In most cases, PWB and PCB are usually treated as synonyms without distinction. In fact, there are differences between PWB and PCB in some cases. For example, PCB sometimes refers to the method of simple printing on an insulating substrate to form a circuit including electronic components, which can be self-contained; while PWB emphasizes the carrier function of components either constitutes a mounted circuit or a printed circuit board assembly(PCBA). Both are usually referred to as printed boards.

Motherboard

Motherboard is an electronic substrate that installs various active and passive electronic components on a large-area PCB, and can realize interconnection with sub-boards and other devices. The communication industry generally calls it a backplane.

Substrate

Substrate carries various active and passive electronic devices, connectors, units, sub-boards and other electronic devices. Such as packaging substrate, SLP, various ordinary PCBs.

Substrate-like PCB (SLP)

what is substrate-like PCB (SLP)
what is substrate-like PCB (SLP)

Substrate-Like PCB (SLP): It is a PCB similar to the specification of the substrate. It is originally an HDI board, but its specification is close to the level of the substrate for IC packaging.

The substrate-like board is still a type of PCB rigid board, but the manufacturing process is closer to the semiconductor specification. At present, the line width/spacing required by the substrate-like board is ≤30μm/30μm, which cannot be produced by the subtractive method, and MSAP (semi- Addition method) process technology, which will replace the previous HDIPB technology.

It is a substrate material that integrates the functions of packaging substrate and substrate. But the manufacturing process, raw materials and design (one piece or multiple pieces) are still inconclusive.

The creator of the carrier-like board is Apple’s new mobile phone. In the iPhone 8 in 2017, it was the first time to use a HDI board similar to the substrate produced by the IC process, which can make the size of the mobile phone lighter, thinner and shorter. The base material of the substrate-like substrate is also similar to that of the substrate for IC packaging, mainly a laminated dielectric film of CCL and ABF* resin of BT resin.

HDI substrate

HDI substrate: Generally, it is manufactured by build-up method. The more times of build-up, the higher the technology of the board.  High-end HDI adopts two or more layering technologies, and adopts advanced PCB technologies such as micro-via, electroplating and filling holes, and laser drilling. Advanced HDI PCB is mainly used in advanced digital cameras, IC substrates, etc.

What are main structure and production technologies of package substrate

What are main structure and production technologies of package substrate
What are main structure and production technologies of package substrate

In high-density packaging, in order to reduce reflection noise, crosstalk noise, and ground noise, and ensure that the characteristic impedance of the connector terminals and cables for connection between layers is matched, it is necessary to develop a high-layer, high-density multilayer wiring substrate.

According to the base material of the substrate, the substrate can be divided into three categories: organic system (resin system), inorganic system (ceramic system, metal system) and composite system.

Generally speaking, inorganic substrate materials have a low thermal expansion coefficient and high thermal conductivity, but have a relatively high dielectric constant, so they have high reliability, but are not suitable for use in high-frequency PCB; Organic substrate materials have a slightly higher thermal expansion rate and poorer heat dissipation, but have a lower dielectric constant, and are light in weight, easy to process, and easy to thin.

At the same time, due to the continuous development of polymer materials in recent decades, the reliability of organic substrate materials has been greatly improved, so they have been widely used.

Structure of package s substrate

The main function of the package substrate is to realize the electrical interconnection between the external circuits of the integrated circuit chip and electronic components.

The core package substrate can be divided into core board and outer circuit, and the interconnection structure of the core package substrate mainly includes buried holes, blind holes, via in pad and lines.

The interconnect structure of the coreless package substrate mainly includes copper pillars and lines. The technical feature of non-nuclear package substrate manufacturing is mainly to manufacture interconnection structures in the packaging substrate—copper pillars and lines—by bottom-up copper electrodeposition technology.

Compared with buried vias and blind vias, the copper pillar is a solid copper metal cylinder structure, which has better performance in electrical transmission. The size of the copper pillar is also much lower than that of the blind hole, directly around 40 μm.

What are package substrate manufacturing technologies

Interconnection between layers of semiconductor packaging substrates and the production method of laminated fine circuits are derived from High Density Interconnection(HDI) / Build up Multilayer (BUM). There are many types of HDI/BUM board manufacturing technologies. Through the survival of the fittest and market selection in terms of producibility, reliability, and cost, the currently relatively mature processes are concentrated in 3-5 types.

How to make layered graphics:
1. HDI
Conventional HDI technology circuit production is completed by subtractive method (etching method), and improved HDI technology mainly uses semi-additive method (electrodeposited copper technology) to complete circuit and microhole production at the same time.

2. Subtractive method
Subtractive, on the copper clad board, through photochemical method, screen printing pattern transfer or electroplating pattern resist layer, and then etch away the copper foil of the non-graphic part or remove the unnecessary part by mechanical means to make a printed circuit PCB.

3. Additive method
Additive method is a method of selectively depositing conductive metal on the surface of an insulating substrate to form a conductive pattern.

4. Semi-additive method
The Semi-Additive Process (SAP) uses graphic plating to increase the thickness of fine lines, while the non-plated thickened non-line areas are quickly etched in the differential etching process, and the remaining parts are reserved to form lines.

Packaging substrate fabrication technology – Improved HDI fabrication technology

High-density interconnect (HDI) packaging substrate manufacturing technology is an extension of conventional HDI PCB manufacturing technology. Its technical process is basically the same as that of conventional HDI PCB. The main difference between the two lies in the use of substrate materials and the accuracy of etching circuits requirements, etc., this technical approach is one of the mainstream technologies for the manufacture of integrated circuit packaging substrates.

Due to the limitation of etching technology, the HDI packaging substrate manufacturing technology has encountered challenges in the ultra-fine line and thinning of the dielectric layer. In recent years, an improved HDI packaging substrate manufacturing technology has emerged.

According to the structure of the core package substrate, the HDI package substrate production process is mainly divided into two parts: one is the production of the core layer; the other is the production of the outer circuit. The improved HDI packaging substrate manufacturing technology is mainly aimed at the improvement of the outer layer circuit manufacturing technology.

A new manufacture technology of packaging substrate--Improved semi-additive method
A new manufacture technology of packaging substrate–Improved semi-additive method

A new manufacture technology of packaging substrate–Improved semi-additive method

The electrodeposition interconnection structure based on the magnetron sputtering seed layer is a brand-new packaging substrate manufacturing technology approach, which is called the improved semi-additive method. In addition, because this technical approach does not require the production of core boards like HDI technology, it is called non-nuclear packaging substrate production technology.

The non-nuclear packaging substrate manufacturing technology does not need to etch copper foil to make electronic circuits, which breaks through the technical bottleneck of HDI in the production of ultra-fine circuits, and becomes the preferred technology for high-end packaging substrate manufacturing. In addition, this technology uses electrodeposited copper to make electrical interconnection structures, so electrodeposited copper technology for interconnection structures is already one of the core technologies for manufacturing non-nuclear packaging substrates.

Conclusion

In high-density packaging, in order to reduce reflection noise, PCB crosstalk noise, and ground noise, and ensure that the characteristic impedance of the connector terminals and cables for connection between layers is matched, it is necessary to develop a high-layer, high-density multilayer wiring substrate.

FAQ

Package substrate is composed of electronic circuit carrier (substrate material) and copper electrical interconnection structure (such as electronic circuit, via hole, etc.), in which the quality of electrical interconnection structure directly affects the stability of integrated circuit signal transmission and reliability determine the normal performance of electronic product design functions.

The packaging substrate belongs to a special printed circuit board, which is a basic component that connects a higher-precision chip or device with a lower-precision printed circuit board.

1. Protect the semiconductor components in the chip
2. Realize the electrical connection between the electronic circuit of the integrated circuit function module in the chip and the external functional components;
3. Provide supports and heat dissipation channels for chip functional components;
4. Provide an assembly platform for other electronic components.
5. Realize the purpose of multi-pin integrated circuit, package product size reduction, electrical performance and heat dissipation improvement, ultra-high density or multi-chip modularization, etc.

1. Classified by substrate material

  • Rigid organic package substrates
  • Flexible package substrates
  • Ceramic package substrates

2. Classified according to the flexibility of the base material

  • Rigid organic packaging substrate
  • Flexible Packaging Substrate
  • Ceramic package substrate

3.Classified by manufacturing process

  • Rigid substrates (including ceramic substrates)
  • Flexible substrates
  • Build-up multilayer substrates (BUM)

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