QFN IC Packages – Panel Level Process for Organic Types

General Definition & Description of Organic QFN Packages

The QFN (Quad Flat No-lead) package is a versatile and efficient packaging technology widely used in various industries for very obvious reasons: low cost, small form factor, plus good electrical and thermal performance. Main components of the QFN package are a lead frame, single or multiple dies, wire bonds and molding compounds. 

The organic QFN package uses organic materials as its substrate or base material. Today, organic substrates have overtaken the ceramics market due to their finer line and space capabilities, better heat management solutions and added flexibility to the design. Organic rigid substrates are classified into two categories: Laminate and Build-Up Types.

Key Characteristics & Features of Organic QFN IC Packages: 

QFN Package types offer good performance, cost-effectiveness and manufacturability suitable for a wide range of electronic applications.

1. Substrate Material: Organic QFN packages typically use organic materials such as epoxy resin or laminate substrates as the base material. These materials are commonly used in standard PCB (Printed Circuit Board) manufacturing processes.
2. I/O Design: Like other QFN packages, organic QFNs have a pad IOs design where the semiconductor die is attached to a center pad structure. The signal IOs are arranged in a grid pattern around the periphery of the package.
3. No Leads: QFN packages are characterized by their leadless design, where the electrical connections are made directly from the IC packages pads to the PCB pads through solder joints on the bottom surface of the package.
4. Cost-Effective: Organic QFN packages are generally more cost-effective compared to other materials such as ceramic, due to the lower cost of organic substrates and their compatibility with standard PCB manufacturing processes.
5. Electrical & Thermal Performance: The electrical performance of organic QFN packages is typically adequate for a wide range of applications. They provide good signal integrity and thermal dissipation properties suitable for various electronic devices and systems.
6. Manufacturing & Assembly: Organic QFN packages are compatible with standard surface-mount assembly processes, including solder paste deposition and reflow soldering. This compatibility facilitates efficient and reliable manufacturing of electronic assemblies.
7. Applications: Organic QFN packages are commonly used in consumer electronics, telecommunications equipment, networking devices and additional applications where compact size, cost-efficiency and adequate performance levels are required.

Key Advantages of the QFN Package

• Packages are lightweight and easy to handle
• Packages are available with a thin profile & small form factor
• Short bond wires are used to connect die and frame 
• Lead inductance of the QFN package is low
• Ideal for applications that require good heat dissipation
• Packages are easily available at a low cost

PROs & CONs of the QFN IC Package

• QFN solutions can offer a wide range of options to the designer 
• The use of organic materials enables numerous material choices 
• Control of CTE, DK, DF and even process-related properties such as TG 

The combination of the right properties will lead to a robust design, however QFN challenges should also be taken into consideration.

Standards & Guidelines 

Designing QFN (Quad Flat No-leads) packages or using components in QFN packages according to existing industry Standards & Guidelines, is critical in order to ensure proper functionality, reliability and manufacturability. When designing with QFN packages, engineers should refer to these Standards & Guidelines to ensure they’re meeting industry best practices.

1. JEDEC Standards:
   • JEDEC MO-220:This standard specifies the outline and dimensions of QFN packages, including lead pitch, pad layout and overall package dimensions. It defines various package sizes and configurations that manufacturers should adhere to.
   • JEDEC JESD51-12: Thermal characterization of semiconductor packages – User Guide.
     
2. IPC Standards:
   • • IPC-7351: Generic Requirements for Surface Mount Design and Land Pattern Standard. This standard provides guidelines for the design of land patterns (footprints) for surface-mounted components, including QFN packages. It specifies dimensions and tolerances for pads and solder mask openings.
     • IPC-2221: Generic Standard on Printed Board Design. This standard provides guidelines for the design of printed circuit boards (PCBs), including considerations for mounting surface-mounted components like QFN packages.
       
3. Manufacturing Guidelines:
   • • Design for Manufacturability (DFM): While not a specific standard, DFM principles are crucial in QFN design to ensure that the package can be manufactured with high yield and reliability. This includes considerations for solder mask, pad dimensions and thermal management.
       
4. Thermal Management:
   • • QFN packages often have exposed thermal pads underneath the package, and it’s important to consider thermal vias, pad size, and layout to ensure effective heat dissipation. Standards like JEDEC JESD51-12 provide guidance on thermal characterization and management.
       
5. Electrical Design:
   • • Ensuring proper electrical connections, signal integrity, and power distribution within the QFN package is critical. IPC standards and manufacturer datasheets provide guidelines on trace width, impedance control and signal routing for QFN packages.
       
6. Reliability & Testing:
   • • Standards such as IPC-A-610 outline criteria for the acceptance of electronic assemblies, including requirements for soldering and mechanical assembly, which are important in ensuring the reliability of QFN packages.
       
7. Specific Manufacturer Recommendations:
   • • Different semiconductor manufacturers may have specific guidelines and recommendations for the design and handling of their QFN packages. These can be found in datasheets and application notes provided by the manufacturer.

Things You Should Know about iNPACK Processes: 

• iNPACK develop and manufacture QFN, IC Packaging Solutions using a Panel Level Processes (PLA). This same process is applied to our LGA and BGA packaging solutions as well. 
• The PLA process allows for optimal design and manufacturability, whereby our customers benefit from more cost-effective, high-performance, high-yield and high reliability IC Packaging Solutions. 
• iNPACK can offer superior customized packaging solutions with a wide range of design options to choose from; embedded coins, hybrid construction substrates (for improved performance), multilayer QFN and many other advanced technologies.

Comparing Packaging Options QFN, LGA & Material Types

Intro

Amid the rapid IC packaging evolution, many different package types have emerged, each embodying its own distinct set of characteristics, advantages and challenges. Differing IC package types can be distinguished by variations in mounting style, pin layout, shape and pin count. Engineers and designers must fully grasp these differences in order to select the most advantageous IC package type for their specific application.

Main Characteristics of QFN (Quad Flat No-leads) & LGA (Land Grid Array)

QFN (Quad Flat No-leads):

• Package Design: QFN packages have exposed pads on the bottom surface of the package, typically arranged in a grid pattern. Leads are absent, which contributes to their compact size and low profile.
• Soldering: QFN packages are soldered directly onto the surface of the PCB, with the exposed thermal pad underneath aiding in heat dissipation. They require careful soldering techniques, such as reflow soldering, to ensure proper connection and alignment.
• Size: QFN packages are generally smaller than equivalent LGA packages due to their flat, leadless design. This makes them suitable for applications where space-saving is crucial.
• Electrical Performance: QFN packages typically offer good electrical performance, with shorter lead lengths and reduced parasitic inductance and capacitance compared to some other package types.
• Applications: QFN packages are commonly used in consumer electronics, telecommunications, and other applications where space, cost, and thermal management are important considerations.

LGA (Land Grid Array):

• Package Design: LGA packages have an array of pads on the underside of the package, but unlike QFN, these pads are typically arranged in a regular grid with no leads extending out from the sides of the package.
• Soldering: LGA packages also require reflow soldering but do not have the issue of exposed leads, simplifying the soldering process. A lack of leads may also reduce the risk of mechanical stress during thermal cycling.
• Size: LGA packages tend to be larger than QFN packages due to its grid array design and the need for sufficient space between pads for soldering and thermal considerations.
• Electrical Performance: LGA packages can offer outstanding electrical performance, often better than QFN packages, especially for high-frequency applications, due to shorter path-lengths and reduced parasitic effects.
• Applications: LGA packages are generally found in applications for high-speed data transfer, such as high-performance computing, servers or networking equipment, where signal integrity and thermal management are paramount.

QFN &LGA Packaging Features

Depending upon application requirements, such as size constraints, thermal management needs, specific demands in electrical performance and cost considerations, each packaging method offers its own distinct advantages. 

QFN Material Types

QFN (Quad Flat No-leads) packages come in different material types. Although there are many determining factors influencing the selection of materials for QFN packages, generally, the material can function to provide mechanical support, aid in heat dissipation and assist manufacturability. Each material type should be examined carefully to reveal the important advantages and considerations related to the application at hand:

3 Types: Ceramic / Organic / Lead Frame

1. Ceramic QFN:

• Material: Ceramic QFN packages are made from ceramic materials, which provide higher thermal conductivity compared to organic materials.
• Advantages:
  • Thermal Performance: Ceramic has excellent thermal conductivity, making ceramic QFNs well-suited for high-power applications where effective heat dissipation is crucial.
  • Reliability: Ceramic materials typically offer better mechanical strength and reliability compared to organic materials, making them more resistant to mechanical stress and thermal cycling.
  • High-Frequency Applications: Ceramic QFNs can maintain stable electrical characteristics at high frequencies due to their low dielectric constant and minimal signal loss.
• Considerations:
  • Cost: Ceramic QFN packages tend to be more expensive than their organic counterparts due to the higher cost of ceramic materials and manufacturing processes.
  • Manufacturability: Ceramic packages may require specialized manufacturing techniques, which can create a more complex production process.

2. Organic QFN:

• Material: Organic QFN packages are made from organic materials, such as epoxy or laminate substrates.
• Advantages:
  • Cost: Organic QFN packages are generally more cost-effective compared with ceramic versions.
  • Compatibility: Compatible with standard PCB manufacturing processes and equipment, simplifying production.
  • Weight: Organic packages are lighter than ceramic, a distinct advantage in weight-sensitive applications.
• Considerations:
  • Thermal Performance: Organic materials exhibit lower thermal conductivity compared to ceramics, which may limit their use in high-power / high-temperature applications.
  • Mechanical Strength: Organic materials may have a lower mechanical strength than ceramics, and can be more susceptible to mechanical stress damage compared to ceramics.

3. Lead Frame QFN:

• Material: Lead frame QFN packages use a metal lead frame, typically made from copper or alloy, with the die attached, and wire bonded to the leads.
• Advantages:
  • Cost: Lead frame QFN packages are often the most cost-effective option of all three package types.
  • Reliability: Lead frames provide robust mechanical strength and stability, making them suitable for a wider range of applications.
  • Ease of Assembly: Lead frame packages are relatively straightforward to assemble and handle during the manufacturing process.
• Considerations:
  • Thermal Performance: Lead frame packages may be limited in thermal conductivity compared to ceramic versions, depending on the specific design and materials used.
  • Size: Lead frame packages tend to be larger compared to ceramic or organic versions due to the structure of the lead frame.

Overall Selection Considerations:

• Application Requirements: Take into account thermal management needs, electrical performance requirements, and mechanical stability and durability.
• Cost Constraints: Review the relative cost-effectiveness of each package type to determine if it’s a match with the budget.
• Manufacturability: Evaluate ease of manufacturing, assembly and test. 
• Performance: Assess electrical characteristics such as signal integrity and high-frequency performance.

In Conclusion 

The choice between ceramic, organic, or lead frame QFN packages will require a careful balanced approach, weighing up numerous factors; such as thermal performance, cost, manufacturability, reliability etc., and how that compares with the requirements of a specific project or application. Each package type offers distinct advantages and considerations that should be evaluated during the design phase.

FYI: Other Names for QFN

QFN packaging can be referred to by different names:

• QFN – quad flat no-lead package
• MLF – micro-lead-frame
• MLPD – micro-lead-frame package dual
• MLPM – micro-lead-frame package micro
• MLPQ – micro-lead-frame package quad
• VQFN – very thin quad flat no-lead
• DFN – dual flat no-lead package

Things You Should Know about iNPACK Processes: 

• iNPACK develop and manufacture QFN, IC Packaging Solutions using a Panel Level Processes (PLA). This same process is applied to our LGA and BGA packaging solutions as well. 
• The PLA process allows for optimal design and manufacturability, whereby our customers benefit from more cost-effective, high-performance, high-yield and high reliability IC Packaging Solutions. 
• iNPACK can offer superior customized packaging solutions with a wide range of design options to choose from; embedded coins, hybrid construction substrates (for improved performance), multilayer QFN and many other advanced technologies.

Advanced QFN Panel-Level Assembly, Near-Hermetic Sealing & Testing

Intro

An important aspect of advanced packaging technologies involves principles of Design-For-Manufacturing (DFM); a system that aims to ensure IC packages can be manufactured efficiently and reliably, with a view towards higher yields and lower costs. In the case of QFN package fabrication, DFM requires examining assembly options, sealing methods and testing processes. 

Sealing Methods

iNPACK QFN – Prepreg Sealing, Proprietary Process: Prepregs, (pre-impregnated materials), offer several advantages over many other types of adhesives or bonding materials, particularly in the context of electronics manufacturing and PCB assembly:

• Controlled Resin Content: Prepregs are manufactured with a controlled amount of resin impregnated into the reinforcing fibers (typically fiberglass). A controlled resin content ensures consistent and predictable adhesive properties during assembly and lamination processes.
• Consistent Thickness: Prepregs are available in various thicknesses and are manufactured with consistent thickness tolerances. This uniformity helps maintain consistent bonding and insulation properties across the PCB during lamination.
• Adhesive & Insulation Properties: Prepregs provide excellent adhesive properties, bonding tightly to copper layers and other materials during the lamination process. They offer insulation between conductive layers, preventing electrical shorts and ensuring reliability of the PCB.
• Mechanical Strength: Reinforcing fibers within prepregs (usually fiberglass) contribute to mechanical strength, which enhances the structural integrity of the PCB, providing robust barrier against mechanical stresses and vibrations.
• Near-Hermetic Sealing: Using prepreg as a sealing process can guard against fine and gross leaks. 
• Thermal Stability: Prepregs are designed to withstand high temperatures during the PCB lamination process (typically around 175-200°C). They maintain their adhesive and mechanical properties under thermal stress, ensuring reliable performance in high-temperature environments.
• Compatibility with Manufacturing Processes: Prepregs are compatible with standard PCB manufacturing processes such as lamination and soldering. They integrate seamlessly into automated assembly lines, for smooth, efficient, cost-effective production.
• Environmental Considerations: Many prepregs are formulated to meet environmental regulations and industry standards for sustainability and safety. They are often halogen-free and comply with RoHS (Restriction of Hazardous Substances) directives.
• Versatility: Prepregs come in many types and formulations, suitable for different PCB designs and requirements. This versatility allows designers to choose prepregs with specific properties, such as high Tg (Glass Transition Temperature) for increased thermal stability, or low Dk (Dielectric Constant) for improved signal integrity.

In Conclusion: Prepregs offer advantages over other adhesives primarily due to their controlled resin content, consistent thickness, excellent adhesive and insulation properties, mechanical strength, thermal stability, compatibility with manufacturing processes, environmental compliance, and versatility in meeting diverse PCB design needs. These characteristics make prepregs a popular choice in the electronics industry to ensure reliable and high-performance PCB assemblies.

B-Stage Epoxy Near-Hermetic Sealing: B-stage epoxy is a reference to an intermediate curing process stage in epoxy resin, where it is partially cured or partially cross-linked. B-stage epoxy resins offer numerous advantages in IC package sealing, described in the following:

• Controlled Curing Process: B-stage epoxy resins allow for a controlled curing process. It remains in a semi-solid state until exposed to elevated temperatures, or specific curing conditions. This controlled curing ability enables precise timing and precise manipulation during the sealing process.

• Adhesive and Sealing Properties: B-stage epoxy resins have excellent adhesive properties, capable of forming strong bonds between different materials used in IC packaging, such as metals, ceramics, and plastics. They are effective in sealing against moisture and contaminants, crucial for protecting semiconductor components.

• Compatibility with Assembly Processes: B-stage epoxy can be applied as a liquid or film during initial stages of IC packaging assembly. This flexibility allows for easier handling and application before the final curing stage. It can be dispensed or coated onto substrates, components, or other areas that require sealing; enabling efficient manufacturing.

• Thermal & Chemical Stability: Once fully cured, epoxy resins exhibit excellent thermal and chemical stability. They withstand high temperatures and resist degradation from chemicals. This ensures long-term reliability and performance of sealed IC packages for a wide range of operating environments.

• Reduced Stress & Warpage: B-stage epoxy resins typically undergo controlled shrinkage during the final curing process, which minimizes stress and warpage in the sealed IC package. This is crucial in maintaining dimensional stability and preventing mechanical failure in packaged semiconductor devices.

• Moisture Protection: Effective moisture protection is critical in IC packaging to prevent corrosion, electrical malfunctions, and reliability issues. B-stage epoxy resins provide a reliable barrier against moisture ingress, enhancing both lifespan and performance of semiconductor devices.

• Cost-Effectiveness: Using B-stage epoxy resins can contribute to cost savings in IC packaging assembly, allowing for efficient application and curing processes, that can reduce labor and material costs associated with sealing operations.

In Conclusion: B-stage epoxy resins offer significant advantages in IC packaging sealing: controlled curing, excellent adhesive properties, compatibility with assembly processes, thermal and chemical stability, stress reduction, moisture protection, and cost-effectiveness. These characteristics make B-stage epoxy resins a preferred choice for reliability, longevity, and high performance, in the fabrication of semiconductor devices for a wide variety of applications.

Panel Level Assembly (PLA) & Sealing Process By iNPACK

iNPACK perform Panel-level IC assembly (PLA), where multiple ICs are fabricated and assembled simultaneously on a larger substrate known as a panel, rather than individually on smaller wafers. iNPACK has also developed a panel-to-panel sealing method, based on prepregs and B-stage epoxy, to achieve near-hermetic sealing packaging qualities.

Advantages & Disadvantages of PLA:

In Conclusion: The suitability of PLA depends on specific manufacturing goals, product requirements, and the ability to manage and mitigate any associated risks.  

Sealing & Molding Panel-Level 

Near-Hermetic Sealing: As used in IC packaging, near-hermetic sealing refers to a sealing technique that provides a certain level of moisture protection and environmental isolation approaching that of hermetic sealing, but without attaining complete hermeticity. Hermetic sealing refers to a package that is completely impermeable to gases and moisture, typically achieved through metal seals and glass-to-metal seals. Near-hermetic sealing aims to minimize moisture and gas ingress into the IC package, to levels that are sufficient for the intended application, without requiring the complexity and cost associated with full hermetically sealed packages. 

Key features & considerations of near-hermetic sealing include:

In Conclusion: Near hermetic sealing in IC packaging strikes an important balance between achieving effective moisture protection and maintaining cost efficiency. It provides a valuable option for the protection of semiconductor devices from moisture-related failures in various demanding environments and applications at a moderate cost.

Near Hermetic Testing Methods: Testing near-hermetic IC packages involves assessing their resistance to moisture ingress (damp penetration) and their ability to maintain a stable internal environment over time. Common methods and considerations for testing near-hermetic IC packages are as follows:

• Visual Inspection: Conduct a visual inspection of the package for any signs of physical damage or sealing breaches. Check for potential compromise points to package integrity such as cracks, gaps, or delamination.

• Hermeticity Testing: Execute various hermeticity testing procedures to evaluate package sealing performance under various conditions. Common test methods include: 

• • Helium Leak Testing: Detects leaks by measuring the rate of helium gas escaping through potential breaches in the package.
  • Bubble Testing: Packages are submerged in a liquid to check for gas bubbles, indicating leaks.
  • Fine & Gross Leak Testing: Using specialized equipment to measure leak rates and to identify potential leaks.
  • Moisture Sensitivity Level (MSL) Testing: Determines package moisture sensitivity levels using industry-standard tests such as JEDEC J-STD-020. It involves subjecting the package to specific temperature / humidity conditions, to check moisture absorption.

• Temperature Cycling: Subjects the IC package to temperature cycling tests that simulate real-world environmental conditions to measure reliability over time, accurately evaluating package responses to changes in temperature and potential moisture condensation.

• Highly Accelerated Stress Testing (HAST): A method of accelerated humidity testing by subjecting the package to extreme levels of temperature and humidity, invaluable in assessing package resistance to moisture-induced failures.

• Environmental Testing: Conduct environmental testing to simulate the conditions the IC package will encounter during its intended use. This may include exposure to temperature extremes, humidity, thermal shock, and vibration to evaluate overall reliability.

• Electrical Testing: Perform electrical tests both before and after environmental stress testing procedure to assess any changes in electrical performance due to moisture ingress or other environmental factors.

• Microscopic Examination: Microscopy techniques are used to examine internal structures and external surfaces for signs of corrosion, delamination, or other damage that may indicate moisture ingress.

• Accelerated Aging Tests: Subjects the IC package to accelerated aging processes to predict long-term reliability. This may include extended exposure to elevated temperatures and humidity conditions.

• Compliance Testing: Ensures that testing methods and results comply with relevant industry standards and customer specifications, such as JEDEC standards for moisture sensitivity and reliability testing.

In Conclusion: Testing near-hermetic IC packages entails carrying out a combination of many different rigorous testing methodologies and procedures in order to compile accurate performance data for this package type. Manufacturers and testing laboratories use these different methods routinely to verify that IC packages meet specific performance criteria and standards in providing robust protection against moisture and other environmental hazards.

Things You Should Know about iNPACK Processes: 

• iNPACK develop and manufacture QFN, IC Packaging Solutions using a Panel Level Processes (PLA). This same process is applied to our LGA and BGA packaging solutions as well. 
• The PLA process allows for optimal design and manufacturability, whereby our customers benefit from more cost-effective, high-performance, high-yield and high reliability IC Packaging Solutions. 
• iNPACK can offer superior customized packaging solutions with a wide range of design options to choose from; embedded coins, hybrid construction substrates (for improved performance), multilayer QFN and many other advanced technologies.