QFN Package Process Flow: Advantages and Types

Key Takeaways

  • The abbreviation QFN stands for quad flat no-lead package.

  • The main parts of a QFN package are a lead frame, single or multiple dies, wire bonds, and molding compounds.

  • In the QFN packaging process flow, singulation can be by shear or saw process. 

QFN IC package

A QFN package is a leadless package of surface mounting technology

There is an increase in demand for ICs in the automotive industry. Various packaging styles are commonly used in automotive ICs: SOP, SOIC, and QFN, among others. QFN IC packages with solderable side walls are used for automotive IC packaging. Designing QFN ICs for automotive applications differs from conventional QFN package process flow. To distinguish between the customized QFN package process flow and the conventional one, it is essential to have a basic idea of the latter.

In this article, let’s explore QFN packages and their process flow. 

IC Packaging 

IC packaging is essential, as it protects semiconductor components internal to the IC from corrosion and other physical impacts. Packaging acts as insulation casing for the IC. Usually, the packaging materials are either ceramic or plastic. IC packaging also facilitates the mounting of electrical contacts of ICs onto the printed circuit board.

Importance of IC Packaging 

The significance of IC packaging is high, as it brings the following features into the design:

  • Functional density
  • Heterogeneous integration
  • Silicon scaling
  • Enhanced device functionality through reduced packaging size
  • Silicon yield resilience 
  • Faster time to market

Let’s look at IC packaging styles in detail.

IC Packaging Styles

Depending on the mounting technology, IC packages are classified as through-hole type and surface mount-type. Among the surface mount IC packages, there are different categories:

  1. Small outline integrated circuits (SOIC)
  2. Small outline packages (SOP)
  3. Plastic leaded chip carriers (PLCC)
  4. Ball grid arrays (BGA)
  5. Quad flat no-lead (QFN) 

We will explore QFN packaging in the upcoming section.  

QFN Packaging and Parts

A QFN package is a leadless package of surface mounting technology. The main parts of a QFN package are:

  1. Lead frame - The most integral part of a QFN package. Determines the overall performance of the IC.
  2. Single or multiple dies - The IC consists of silicon dies, which are connected to the PCB using surface mount technology.
  3. Wire bonds - The lead frame and die are connected using copper or gold, called wire bonds.
  4. Molding compound - Molding compound helps achieve electrical insulation, corrosion resistance, and reliability in the QFN package.

Advantages of QFN

  1. Low cost
  2. Good electrical performance
  3. Good thermal performance and heat dissipation
  4. Small form factor and lightweight
  5. Short bond wires connecting the die and lead frame
  6. Low lead inductance due to short bond wires

Types of QFN Packages

QFN packages are available in different types.

  1. Air-cavity QFN - Consists of a plastic or ceramic lid, copper lead frame, and an open-without-seal-plastic molded body. Air cavity QFN packages are used in microwave systems with frequencies ranging from 20 to 25 GHz.

  2. Plastic molded QFN - Plastic molded QFNs are cheaper than air-cavity QFNs. They consist of a plastic compound and copper lead frame. This type of QFN package is used in 2-3 GHz frequency applications. There is no lid on plastic molded QFN packages.

  3. Punch type QFN - This type of package is molded in a single mold cavity format where a                                   tool is used to separate the mold cavity.

  4. Sawn type QFN - The molding process of sawn type QFNs, called the mold array process, cuts a massive number of boxes into smaller parts.

  5. QFN with wettable flanks - This type of QFN helps designers visually check that the pad is mounted to the PCB through the elevation provided by the wettable flanks.

  6. Flip-chip QFN - A cheap modeled package offered by flip-chip QFNs. This package uses flip-chip interconnection to establish electrical connections.

  7. Wire bond QFN - In this package, wires are used to connect the PCB to the chip terminal.

QFN Packaging Process Flow

The block diagram below shows the various steps involved in QFN package assembly.

QFN Package Process Flow

Designing QFN Packages of Different Singulations

In the QFN packaging process flow, singulation can be by shear or saw process. Shear-singulated QFN packages are designed individually, whereas saw-singulated QFN packages are designed in bulk. Cadence can assist you in designing QFN IC packages for automotive, aerospace, and commercial applications.

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