Picking the Right Heat Sink Attachment to Avoid Costly PCB Damage

The design of a printed circuit board (PCB) is a complicated process that requires engineers to consider a number of different issues before the board is ready to move beyond prototype and into production. Engineers must think about the physical constraints of a board on component size and placement, the electrical interaction between components, the signal loss through wires and traces, and the thermal management of each component and the system as a whole. [1]

Heat Sink Attachment

ATS maxiFLOW heat sink with superGRIP attachment on a PCB. (Advanced Thermal Solutions, Inc.)

With all of that to consider, it is no wonder that many designs go through several iterations before moving into the production stage. Since the process is already complex and there is a certain amount of trial-and-error in designing a PCB, engineers will look for ways to avoid unnecessary rework that will add significant cost to the project in terms of both time and money.

As noted in a previous article, the type of heat sink attachment technology that an engineer chooses will impact the ease with which a design can be reworked and the amount of damage to the board that will be caused if a change needs to be made.

Push pins, threaded standoffs and z-clips require holes or anchors be drilled into a board, which leaves permanent damage if a component needs to be moved to a new location and could also impact signal routing. There is even the possibility of a short in installation, which also would damage the board. [2]

Non-mechanical attachments such as thermally conductive tape and epoxy are not guaranteed to provide the optimal thermal management because there is “risk of die damage and poor thermal performance due to uneven heat sink placement,” according to a case study from the Altera Corporation. [3]

The case study also said that thermal tape and epoxy have “high risk of damaging the device or PCB” when compared to mechanical attachment technology coupled with thermal interface material (TIM) or phase change material (PCM). In fact, to remove a heat sink attached with epoxy requires an even temperature of 115-120°C.

As the video below shows, removing thermal tape from a heat sink (even one that is not attached to a board) requires a lot of work and tools. If the heat sink is attached to a component, the process to remove it could damage the board or other devices in the vicinity:

A recent chart from NEMI (National Electronics Manufacturing Initiative) indicated that the cost of assembly can be very high per I/O (input/output) on the PCB – considering some of the new BGAs have hundreds of I/O and there are dozens of BGAs on the board, the cost can be prohibitively expensive to put together a board irrespective of the product sector. [4] Obviously, full reworks necessitated by the use of damaging heat sink attachments raise those costs exponentially.

Heat Sink Attachment

Board assembly roadmap from NEMI showing the conversion costs by product sector. [4]

Advanced Thermal Solutions, Inc. (ATS) has created a mechanical attachment technology that makes rework easy and allows engineers to make changes to the design without damaging the PCB or the components. superGRIP™ is a two-part attachment system with a plastic frame clip that fastens around the edge of the component and a metal spring clip that fits between the fins of the heat sink and quickly and easily attaches to the frame.

As the video below demonstrates, superGRIP™ can be installed and removed with common household tools and will provide a steady, firm pressure to ensure optimal thermal performance of the heat sink and the reliability of the device:

The advantage of superGRIP™ is not limited to its ease of use and the time and money that will be saved in reworking a PCB design. The pressure strength and security of the superGRIP™ attachment system allows the use of high-performance phase change materials that can improve heat transfer by as much as 20 times over standard thermal tapes. [4]

superGRIP™ comes with Chomerics Thermflow T-766, a foil PCM with a thickness of 0.0035 millimeters that has an operating range of -55°C to 125°C. According to Chomerics, the T-766 and other traditional non-silicone thermal interface pads “completely fill interfacial air gaps and voids. They also displace entrapped air between power dissipating electronic components. Phase-change materials are designed to maximize heat sink performance and improve component reliability.” [5]

Chomerics added, “Upon reaching the required melt temperature, the pad will fully change phase and attain minimum bond-line thickness (MBLT) – less than 0.001 inch or 0.0254 mm, and maximum surface wetting. This results in practically no thermal contact resistance due to a very small thermal resistance path.”

The combination of frame and spring clip provides uniform force over the heat sink and ensures no movement to optimize the impact of the PCM, while not damaging the solder holding the BGA component in place on the board. ATS engineers designed the attachment technology so that the in-plane and normal forces of both the frame and the spring clip hold the heat sink without stressing the solder even through NEBS (Network Equipment Building Systems) shock and vibration testing. [6]

Save time, save money, and avoid unnecessary headaches during the design phase by using ATS superGRIP™ technology.

References
[1] http://www.electronicdesign.com/boards/11-myths-about-pcb-layout
[2] “How the maxiGRIP™ attachment system impacts component mechanical behavior,” Qpedia Thermal eMagazine], May 2008.
[3] https://www.altera.com/content/dam/altera-www/global/en_US/pdfs/literature/an/an657.pdf
[4] http://thor.inemi.org/webdownload/newsroom/Articles/CA0599.pdf
[5] https://www.qats.com/cpanel/UploadedPdf/ATS_superGRIP_Launch_Release_
FINAL_with_Photo_0427092.pdf

[6] http://vendor.parker.com/852568C80043FA7A/468ea5de5ac341d385257d39005641c7/
9A63F6EE5B922F278525787600620419/$FILE/Phase_Change_Excerpt-5-08.pdf

[7] “How the maxiGRIP™ attachment system impacts component mechanical behavior,” Qpedia Thermal eMagazine, May 2008.

For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit www.qats.com or contact ATS at 781.769.2800 or ats-hq@qats.com.

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