There are six main methods for heat sink attachment.
Table: Heat Sink Attachment Methods
lists their advantages and disadvantages.
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Thermal tape
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Thermally conductive adhesive or glue
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Wire form Z-clips
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Plastic clip-ons
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Threaded stand-offs (PEMs) and compression springs
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Push-pins and compression springs
Table 12-1:
Heat Sink Attachment Methods
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Attachment Method
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Advantages
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Disadvantages
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Thermal tape
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Generally easy to attach and is inexpensive.
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Lowest cost approach for aluminum heat sink attachment.
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No additional space required on the PCB.
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The surfaces of the heat sink and the chip must be very clean to allow the tape to bond correctly.
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Because of the small contact area, the tape might not provide sufficient bond strength.
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Tape is a moderate to low thermal conductor that could affect the thermal performance.
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Thermally conductive adhesive or glue
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Outstanding mechanical adhesion.
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Fairly inexpensive, costs a little more than tape.
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No additional space required on the PCB.
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Adhesive application process is challenging and it is difficult to control the amount of adhesive to use.
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Difficult to rework.
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Because of the small contact area, the adhesive might not provide sufficient bond strength.
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Wire form Z-clips
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It provides a strong and secure mechanical attachment. In environments that require shock and vibration testing, this type of strong mechanical attachment is necessary.
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Easy to apply and remove. Does not cause the semiconductors to be destroyed (epoxy and occasionally tape can destroy the device).
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It applies a preload onto the thermal interface material (TIM). Pre-loads actually improve thermal performance.
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Requires additional space on the PCB for anchor locations.
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Plastic clip-ons
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Suitable for designs where space on the PCB is limited.
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Easy to rework by allowing heat sinks to be easily removed and reapplied without damaging the PCB board.
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Can provide a strong enough mechanical attachment to pass shock and vibration test.
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Needs a keep out area around the silicon devices to use the clip.
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Caution is required when installing or removing clip-ons because localized stress can damage the solder balls or chip substrate.
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Threaded stand-offs (PEMs) and compression springs
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Provides stable attachments to heat source and transfers load to the PCB, backing plate, or chassis.
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Suitable for high mass heat sinks.
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Allows for tight control over mounting force and load placed on chip and solder balls.
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Holes are required in the PCB taking valuable space that can be used for trace lines.
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Tends to be expensive, especially since holes need to be drilled or predrilled onto the PCB board to use stand-offs.
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Push-pins and compression springs
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Provides a stable attachment to a heat source and transfers load to the PCB.
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Allows for tight control over mounting force and load placed on chip and solder balls.
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Requires additional space on the PCB for push-pin locations.
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