Greetings from the author, Mr. Yamashita

Introduction of publication contents

Don't you still think that the heat problem is someone else's problem? However, isn't there actually a lot of problems caused by heat? Due to the high performance of devices, the high density of substrates, and the miniaturization of equipment, the problem of heat has become something that even designers cannot ignore.

Now is the time to know about the heat problem. We will introduce the basics of heat problems, from the mechanism of heat transfer to analysis and solutions.

1. Thermal analysis is the egg of the trend

"I'm interested in thermal analysis", such electrical designers are increasing these days. The use of high-performance devices increases power consumption, the miniaturization of equipment increases the density of boards, and the miniaturization of equipment also reduces the space for heat dissipation, while the components for heat dissipation Isn't there a situation where you don't want to use it as much as possible to achieve cost reduction? Therefore, it seems that designers are beginning to take an interest in the keyword "thermal analysis" as a means to prevent problems before they occur.

The problem of heat did not suddenly emerge in the last few years. The history of simulators for analyzing heat also goes back more than 20 years. In the past, the range of analysis tools used may have been limited, such as when multiple ultra-high-performance devices were used or when used under special conditions, but these days, consumer products are also being targeted. has increased. If you make a mistake in heat countermeasures, it may lead to a big loss.

I expect thermal analysis tools to be a field that will develop in the future, but the current situation is that signal integrity is spreading from a few analysis professionals to every electrical designer. I think it's similar to the first stage. As the number of thermal problems increases, it will become difficult for a thermal analysis specialist to follow up on everything, and each electrical designer will have to take on that role. Before that happens, I would like to make the minimum preparations, but it seems that electrical designers' awareness of thermal analysis tools is still low.

Up until now, we have been talking about thermal analysis in one word, but thermal analysis tools can be divided into several types, and the analysis tool to be used differs depending on the target to be analyzed. For example, depending on the analysis target, such as a single package, a substrate, or the inside of a housing that contains them, the tools used will differ, and the person in charge will also differ. Circuit boards are often used by those in charge of electricity, and enclosures are often used by those who specialize in thermal analysis because the hurdles for analysis increase.

In the case of transmission line problems, the tools used differ depending on the subject, such as a transmission line analysis tool and a rule checker in the case of EMI. Finding the cause of the problem takes time and effort. If you're an electrical designer, you'll probably use a thermal analysis tool for your board. If you have a thermal analysis tool for your board, you will be able to grasp the thermal problems that may occur on the board in advance, and use them as clues to solve them from the root. Thermal analysis tools for this board may become a trend in the future.

2 Know the mechanism of heat transfer

The easiest way to solve the heat problem is to prevent heat from being generated, but in order to satisfy the product specifications, a certain amount of heat is unavoidable. I think that clearing is also an essential element for making good products. You will have to mobilize all possible means to deal with heat, but if you understand correctly how heat is transmitted in that case, you can manage heat under limited conditions. It will help you take action.

There are three ways of transferring heat: To put it the other way around, there are only three, so if you make good use of each characteristic, it will help you find a way to effectively discharge the generated heat.

● Heat conduction: Heat is transferred directly from the IC to the board through pins, etc.
● Thermal convection : Heat transfer from the surface of the IC to the air as convection.
● Heat Dissipation : Directly transfers heat when there is a temperature difference between two distant objects.

In other words, when you directly touch a warm can of coffee, you feel the heat, and this is heat conduction.

The oil heater warms the room because the air that touches the warm oil heater circulates in the room, and this is due to thermal convection. It feels warm when exposed to direct sunlight. That which is not directly touched or felt warmth through the air is heat dissipation.

On the board, the size of the components also affects their ability to transfer heat to the outside. The larger the area in contact with the air, the easier it is to dissipate heat, so large parts are more advantageous in dissipating heat. On the other hand, even parts with low power consumption can get surprisingly hot if they have a small surface area.

Also, if high-temperature components are densely arranged, the effect of heat dissipation by thermal convection will be reduced, so careful consideration is required when arranging components.

High heat will affect the performance and life of the device. Have you ever heard of the law called "10°C double rule"? Doubling the temperature halves the life of the part. In particular, electrolytic capacitors are parts that are vulnerable to heat. There is a need for strict measures to prevent the failure rate from increasing.

3 Solving problems with what-if analysis

I would like to talk about a thermal analysis tool specifically for boards. A thermal analysis tool dedicated to the board can import the information necessary for analysis from the board design CAD, so the labor required for analysis can be reduced to some extent, and the analysis speed can be expected, so it is handled by electrical designers. Even if you do, you can minimize the burden.

As with signal integrity (SI) analysis, I think that operability and analysis speed are necessary conditions when designers use analysis tools. Cumbersome and slow tools make what-if analysis daunting and discouraging.

The board thermal analysis tool can receive information on board shape, component placement information, and component size from the board design CAD. By adding information on the power consumption of each component and the environmental conditions in which the board is placed, it is possible to see the analysis results.

I don't think it's necessary to reiterate the importance of pre-analysis, but what-if analysis is effective in the pre-analysis stage. You can try it.

For example, moving parts on the analysis tool, adding a heat sink, adding a plane, and changing the performance of the fan attached to the chassis. These changes can be completed only in the tool, so you can check it in a much shorter time than creating the real thing, and it has the effect of being friendly to your wallet.

In this way, what-if analysis makes it possible to predict temperature without actually creating boards with various patterns. It's not just the substrate temperature that can be checked. It is possible to check a wide range of things, such as checking whether the temperature of a single component exceeds the standard value, or whether there is a large amount of thermal stress that causes board distortion.

Thermal analysis tools for boards can be very easy to work with, but thermal analysis is also deep. Recently, it seems that seminars on countermeasures against heat are being held here and there, so if you think you will need it in the future, I recommend that you gather information from various places from now on. increase.

Related information

▶ Board verification tool / HyperLynx

Seminar/Workshop

▶ [Online Seminar] PCB Board Noise Analysis Seminar Basics of Signal Quality and Transmission Line Simulation <Free>

We will explain the basic principles and causes of signal distortion, general countermeasures, and verification examples using actual designs using HyperLynx, which can be purchased from 1 million yen or less. Participation is recommended not only for those who feel that SI and PI measures are necessary, but also for those who outsource SI/PI analysis at high cost.

▶ Events and seminars related to Siemens EDA

Inquiry