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Heat Sink Fabrications Guide QUICK & EASY GUIDE TO CHOOSING A HEAT SINK Boyd Heat Sink Fabrications Guide A Quick & Easy Guide to Choosing a Heat Sink Overview Over several decades, Boyd has built the world’s largest portfolio of heat sinks and thermal management technologies. We’ve utilized this experience and knowledge to develop our Heat Sink Reference Guide to help you find the right heat sink solution. This article covers the most popular passive heat sink types, integrations, customizations and how to choose the right fabrication and fin type for your application. Choosing the correct heat sink is essential to optimized cooling, with higher performance in more compact geometries at the correct price point. Our quick reference guide will help you to decide where to begin in building and choosing your heat sinks. CONTENTS Heat Sink Basics … 2 Quick Overview in Heat Sink Classification Heat Sink Fabrications … 3 Stamped Board Level Extrusions Skived Bonded Fin (& Brazed) Zipper Folded Fin Die Cast Additional Components … 9 Thermal Interface Materials Fans & Blowers Embedded Heat Pipes Next Steps … 11 Get started finding your ideal heat sink. 1 Heat Sink Reference Guide www.boydcorp.com October 2021 Heat Sink Fabrications Guide QUICK & EASY GUIDE TO CHOOSING A HEAT SINK HEAT SINK BASICS The heat sink is one of the most fundamental components in cooling electronic devices. For any heat source that cannot be properly cooled through its own conduction cooling and needs more efficient cooling than a heat spreader, a heat sink is necessary to move heat away from the source and dissipated through more optimized conduction or convection. Heat sinks are primarily constructed with a base and fins. The base is typically a planar surface that makes contact with the heat source and spreads the heat from the hot spot to the fins. Fins can be cut or constructed in any number of geometries which often run perpendicular to the base to disperse heat. The goal is to optimize the surface area of the heat sink so that the most heat can be transferred and dissipated. With rare exceptions, heat sinks are made of a thermally conductive metal, the most common being Aluminum. Aluminum has a thermal conductivity of 235 watts per Kelvin per meter and is lightweight and inexpensive, making it ideal for lighter, more cost-efficient heat sinks. Copper is also a popular choice. Although copper is more expensive and heavier, it can be necessary for high performing applications due to its high thermal conductivity at 400 W/mK. Finally, engineers often class heat sinks into “natural” convection or “forced” convection. Natural convection (Passive) heat sinks maximize surface area and conduct heat without the addition of active components. Forced Convection (Active) heat sinks are designed to utilize components such as fans and blowers to force cooler air across the fins, creating turbulence and increasing the cooling performance of the heat sink. Basic heat spreaders are used in smaller applications that emit very little heat and a heat sink is unnecessary. Natural convection heat sink. Heat spreads across the base and up the fins. Force convection heat sink utilizing an impinged fan to force air across the fins and create turbulence. There are variations in fin density and length between convection types even when it is a very similar construction. 2 Heat Sink Reference Guide www.boydcorp.com October 2021 Heat Sink Fabrications Guide QUICK & EASY GUIDE TO CHOOSING A HEAT SINK HEAT SINK FABRICATIONS STAMPED BOARD LEVEL Board level heat sinks can be stamped or extruded. Stamped heat sinks are made with sheet metal that has gone through a progressive punching process where details and features are added with each stamp of metal going through the punching die. Stamped heat sink geometries are designed for specific electronic package types to ensure optimized fit and function on a PCB. These heat sinks can be passive or active based on the addition of a fan which is typically used to increase air flow across the entire board or system. Benefits • • • • • Ideal for Lower Power Applications (0-5W) Options for Fast & Easy Assembly Low Cost Scalable High Volume Catalog Options for All Package Types Trade Offs & Limitations • • • Not for Applications over 5W Size Limitations, no larger than 50mm Can only be Used on One Device – not for cooling multiple heat sources Questions to Ask Yourself • • • • • • • 3 What package or device are you cooling? What is the maximum ambient temperature that the device needs to operate in? How much power is your device dissipating? What is your maximum device case temperature? How much room do you have for your heat sink? What is your planned component mounting method, holes, adhesive pad, clip? Will there be any fans and where will they be placed? Standard Specifications Height Range: 10mm - 50mm Material: Aluminum Finish: • Black or Clear Anodize • Tin-Plated Approx. Thermal Resistance (°C/W): • Natural Convection: ~8°C/W - 12°C/W • Forced Convection: (20LFM – 1000LFM): ~2°C/W – 8°C/W Heat Sink-to-Board mounting methods include: • Solder Tabs & Pins • Interference Fit with Integrated Clips or SlideOn Features • Through-hole Hardware – Screws & Nuts • Free-standing (sink mounted to component; component mounted to board) • Epoxy-bonded • Tape Attach Dissipating component can be mounted to device by: • Soldering • Integrated spring clip • Push-on spring clip Heat Sink Reference Guide www.boydcorp.com October 2021 Heat Sink Fabrications Guide QUICK & EASY GUIDE TO CHOOSING A HEAT SINK EXTRUDED ALUMINUM Extruded Aluminum is one of the most popular and cost-efficient fabrications. Extruded heat sinks range in size based on application, smaller for board level or larger for medium power applications. They can be designed for passive or active cooling based on fin shape and pitch. Board level extruded heat sinks are common for packages such as BGAs and FPGAs. Choosing the right extruded heat sink is largely based on the profile needed. Extruded heats sinks are made by creating a profile die that determines fin density, pitch, and length, as well as the base height and width. Softened Aluminum is pushed through the die to create a long bar, known as a raw bar, with the same profile and size as the die. The bar is then cut into smaller, standard shaped bars/rectangles or custom lengths. These are further machined and finished to create customized heat sinks. This process is fast, cost-efficient, and scalable; which is why many consider extruded heat sinks first when searching for a solution. Benefits • • • • • Ideal for Low to Medium Power Applications Fast & Cost-Effective Scalable High Volume Simple Customizations One-piece construction for Limited Thermal Resistance Trade Offs & Limitations • • • Not for High Power Applications Size Limitations, dimensions cannot be greater than approximately 23” W, 47” L Finishing Limitations on larger sizes Questions to Ask Yourself • • • • • • • 4 Are you using Natural or Forced Convection? Will you need machining? What is the maximum ambient temperature that your device will be operating in? How much power is your device dissipating? What is your maximum device case temperature? What is your device size and heat source footprint? How much room do you have for your heat sink? Standard Specifications Fin Aspect Ratio: 15:1 Materials: • Aluminum • Copper • Stainless Steel • Inconel Smaller Footprint for Applications with Limited Space High Thermal Performance Good for Forced Convection, No limit on Air Flow length Tight Fin Pitch High Fin Aspect Ratio Easily Integrated, High Design Flexibility Lower Tooling Costs Trade Offs & Limitations • • Not for Applications with High Vibration or Shock Cannot be used when the thermal resistance is required to be below 0.01°C/W Questions to Ask Yourself • • • • • • • 6 General Guidelines: • Fin thickness typically ranges from .010” to .080” • Brazed, soldered or thermal epoxy bonded depending on thermal resistance required • Fins can easily be non-uniform geometry, especially length, with no post machining How much power needs to be dissipated? What is the footprint and location of the heat source? What is the ambient temperature and max heat sink temp? (or needed thermal resistance) What are the geometrical or weight constraints, overall dimensions? Do you need a fan? What are your material preferences? What is your target cost? Heat Sink Reference Guide www.boydcorp.com October 2021 Heat Sink Fabrications Guide QUICK & EASY GUIDE TO CHOOSING A HEAT SINK ZIPPER FINS Zipper fin stacks are made from a series of individual stamped sheet metal fins that are folded and zipped together using interlocking features. Fin lengths and gaps vary based on the stamping die. Fins can be closed to create a finned duct or left open for multi-directional air flow based on application requirements. The fin stack is typically soldered, brazed, or epoxied to a heat sink base or heat pipes for a full thermal assembly. The joining of the fins at the top and bottom creates increased mechanical stability for more durable heat sinks. Zipper fin stacks offer a high level of design flexibility that enables their use in highly integrated solutions with a range of technologies from embedded and transport heat pipes and vapor chambers to fans and larger systems. Benefits • • • • • • • High Thermal Performance Ideal for Forced Convection Easily Integrated, High Design Flexibility Lower Tooling Costs Lighter Weight Can be used to increase Heat Pipe Efficiency Increased Mechanical Integrity Trade Offs & Limitations • Some limits to Low Thermal Resistance Requirements Questions to Ask Yourself • • • • • • 7 Are you utilizing forced convection? How much power needs to be dissipated? What is the footprint and location of the heat source? Do you have vertical space? What is the ambient temperature and max heat sink temp? (or needed thermal resistance) What are the geometrical or weight constraints, overall dimensions? Are you considering heat pipes? Standard Specifications Materials: • Aluminum • Copper • Inconel Finish: Nickel Plating Zipper Styles: • Closed • Open • Mixed General Fin Dimensions: • Length: