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Top 10 Tips for Efficient Thermal Management

Tue, 12/20/2011 - 6:38am
W. John Bilski, Senior Engineer, Thermacore Inc.

With more medical devices containing electronic components, the heat generated by these components becomes a greater issue for the designers of the finished products. As such, consulting with a thermal management expert prior to designing a new device becomes a high priority “to do” item. This article provides a number of additional tips to address thermal management challenges.

As the electronic components in medical devices become smaller and more powerful, they have reached the point where they can now generate enough heat that, left uncontrolled, can impact the reliability and performance of the device. When designing a new device, engineers should consider whether a particular component may require a cooling solution to ensure that the device performs as expected. The following tips can help designers plan for the most effective thermal management solution for their specific device.

1. Collaborate—Consult with a thermal management expert when the device is in the early stages of development. If a cooling solution is not considered until after the device fails testing, the most appropriate product may not fit in the space available. The unexpected charges will increase the cost of the device for the end-user, and it may no longer be able to compete against similar products in the marketplace.

2. Prepare—If unsure whether the electronics in a product will generate too much heat, consider purchasing modeling software that helps predict the thermal needs of the design before building prototypes. Alternatively, design engineers can consult with a company specializing in thermal management who already have the modeling software and have been trained in how to use it. The software can analyze various components in a device and predict at what temperature the device can operate without overheating. This software is best used early in the design process, especially if engineers are creating a new design rather than modifying an existing one. After using the software, the design can be easily modified, if necessary, to include the most appropriate cooling solution.

3. Choose the simplest cooling solution possible—A component that dissipates a lot of power may not necessarily require a large, complex thermal solution. If the device can handle high junction temperatures (some components are rated to 200°C), it may require a smaller heat sink than a device generating significantly less heat, but which may be rated for only 65°C.

4. Avoid cross-contamination—A 65°C rated component and a 200°C rated component may not require a heat sink. However, when you put them on the same printed wiring board (PWB), the board may conduct enough heat from the component operating near 200°C to the 65°C rated component to cause it to overheat. Likewise, even if the components are on separate PWBs, the 200°C rated component located upstream in the air flow may heat the airstream to the point that the 65°C rated component can no longer remain below 65°C.

5. Be as specific as possible with details, no matter how minor—If choosing to collaborate with a thermal management expert, be as specific as possible with the details. Take, for example, a custom integrated circuit that measures 7/8 in. by 7/8 in. and generates 100 watts of energy, which results in a relatively low watt density. However, instead of the heat being dissipated over the entire device, the design may actually have the wattage concentrated in two or more smaller areas of the device, that may each measure 1/4 in. by 1/4 in. These areas with more concentrated heat will naturally be hotter. If the thermal solution does not take that into account, the device may still run too hot. By being specific with details, designers can save costs by having the most accurate models and developing the most appropriate cooling solution the first time.

6. Choose appropriate materials—Consider the application of the device and choose the most useful material. For example, copper heat pipes, which are common components in thermal solutions, are not appropriate for surgical instruments that come into contact with the human body or bodily fluids,because copper can be toxic to the skin and other organs. Depending on the environment, copper may also be susceptible to corrosion. Alternatives include gold plated heat pipes, which retain the conductivity of the heat pipes and eliminate the potential for corrosion or harm to patients.

7. Analyze sterilization needs—Although some surgical devices are designed for single use, others need to be thoroughly cleaned before being used again. Ensure that the device can handle the rigorous and stringent sterilization requirements that operating rooms and other medical applications may demand, including certain forms of radiation, heat, and/or chemicals like alcohol, ethylene oxide, and bleach.

8. Consider regulatory requirements—Because operating rooms and other environments where medical devices are used are heavily regulated, consider any federal restrictions or requirements that may apply when choosing a solution. Many thermal solutions are required to fulfill strict regulations above and beyond the medical requirements. For example, some heat exchangers are rated NEMA 12 (prevents dust from contaminating electronics in a device or enclosure) or NEMA 4 (prevents dust and liquid from entering the device).

9. Determine power needs—Depending on the size and the amount of heat generated from the electronics in the device, it may be cooled by air alone (otherwise known as natural convection) or require a fan (forced convection) to move the heat outside the device. If the amount of heat requires forced convection, make sure that the device has room for the fan and the necessary additional power it will require.

10. Be flexible—When the prototype fails due to unforeseen thermal issues, it is easy to say that the design cannot be changed and the thermal solution must work around the current design. A better solution may involve changing other components in the assembly in addition to adding the thermal solution. If making a million widgets a year, should designers want the lowest cost prototype or the lowest cost final design? Similarly, investing a little extra time at the prototype stage may result in the company saving thousands of dollars in production costs over the life of the product line.

By following the tips outlined in this article, designers can save significant costs that can result from not considering thermal management until a design has already been planned, built, and tested. If designers don’t consider a cooling solution at the beginning of the design process, the costs can easily escalate beyond the budget and may limit choices for the most appropriate thermal solution.

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