Product Type: Heatsinks

Forced convection is a mechanism in which fluid motion is generated by an external source like a pump, fan, or other device. While the term forced convection can be used to refer to any fluid, it is most commonly associated with forced air cooling. Because of the usually high airspeeds associated with forced convection, significant amounts of heat can be transported quickly and efficiently. The amount of surface area on the heat sink is an important factor in helping meet the desired thermal performance, but too much surface area will cause the heat sink to have a large pressure drop. The greater the drop in pressure, the greater the strain put on the fan, which results in decreased fan performance. Wakefield Thermal engineers will help find the optimal operation point to achieve your thermal requirements.

Skived Fin heat sinks can be an alternative to extruded heat sinks when looking for a fin density that can’t be achieved by extrusion technology. Skived heat sinks can be manufactured from either copper or aluminum and usually have 0.5 (0.020”) thick fins. Skived heat sinks are produced using a series of sharp knives that, as they pass over the material, curl up a small thickness of metal which is then bent vertically to form the fin. Skived fins are produced from a bar of material that is approximately 16 feet in length and then cut to length as required by the final application. The final heat sink can be machined using normal fabrication techniques. Because of the thin fins, care must be taken in handling to prevent damage. It is suggested that a shroud be placed over the fins to help prevent damage.

Zipper Fin heat sinks can be an alternative to both extrusion and skived when looking for high-density structures. Unlike skived fin, a zipper fin heat sink is an assembly of a base and a fin stack that are soldered or bonded together. The fin stack is created using a set of individually stamped fins which are joined together in several locations along the top and bottom edges. The location and number of joining features are determined by the design. Since the fins are stamped individually, they may have any shape and include other stamped features. While zipper fins are most often used with a base plate, they can also be used with heat pipes. Hole(s) is/are stamped into the fins and the fin stack set is placed on a series of heat pipes to form the heat sink. This type of construction is generally found in CPU coolers. Zipper fins can be manufactured from either copper or aluminum and it is possible to mix the different materials within a fin stack. The base can be either aluminum or copper as well. Depending upon the materials used, the finish is either a nickel plate or a chromate, either of which will improve the thermal performance and provide environmental protection.

Ohmite now carries a line of heatsink solutions that are specifically designed for your BGA and PBGA applications. Ohmite’s heatsinks provide a low-cost thermal solution for these specific packages in multiple sizes. Our heatsink solutions can be attached to devices with adhesive thermal tape, making installation as seamless as possible. Custom heatsinks are available upon request.

Board-level heat sinks are so named because they are generally attached both to the device and the PCB. Usually constructed as either a stamping or an extrusion, these heat sinks are designed for common package sizes like T0220, T0247, and D2pak. Stamped heat sink can have features that clip onto the device so that a screw or secondary clip is not required. Stamped heat sinks have bent/twisted fins to improve the thermal performance in either natural or forced convection. Aluminum stampings are anodized for improved performance in natural convection. If the heat sink is to be mounted to the PCB, then a solderable tab or pin can be attached to the heat sink.

BGA heat sinks are so named because they are mounted to BGA devices, but are actually just simple extrusions. BGA heat sinks are usually crosscut to convert the extruded fins into pins that allow them to be used in more diverse applications. The number and size of the crosscuts are dependent upon the environment. Because BGA heat sinks are generally small, the attachment of the heat sink is a challenge. The heat sinks can be either attached to the device or to the PCB depending upon the application and the mechanical requirements. Thermal tape/Epoxy is a common method usually associated with low-power devices. While not the best thermal interface material, they serve their purpose.

Pushpins are another common attachment method and require two small holes in the PCB. Because the holes are generally just outside the boundaries of the device, they can make chip routing difficult. The pushpin, which can be made from plastic or metal, uses the energy of a small spring to provide enough force to keep the heat sink in place.

In cases where the pushpin’s holes are not practical, anchors and wire clips can be used as an alternative. The anchors are either soldered to the PCB using two small holes per anchor or can be installed in a routed slot in the PCB. In the case of the slot, the anchor is installed from the back side of the PCB and is held in place by the compression force in the anchor design. The advantage of the anchors is that their location is much more flexible and can be moved out of the way of traces in the PCB. A wire clip is a small diameter wire that is bent into various shapes that when deformed, engages with the anchors and applies a force to the heat sink to hold it in location. The actual shape of the wire clips is dependent upon the location of the anchors, the heat sink design, and the amount of force required. Multiple wire clips can be used with a single heat sink in applications where a higher force is required. Wire clips are removable and allow the heat sink to be reused in the case of a reworked device.

Since the pushpins and wire clips are a mechanical attachment method, it opens up the type of interface material that can be used between the heat sink and the chip, which can lead to better performance.

Extruded heat sinks are the most common heat sink used for thermal management today. They are manufactured by pushing hot aluminum billets through a steel die to produce the final shape. The most common aluminum alloy is 6063-T5, but other 6XXX alloys can also be examined as needed. When the material is extruded, the initial sticks are 30-40 feet in length and are very soft. The material is stretched by grabbing both ends to produce a straight stick. After stretching, the material can be either air or overaged depending upon the required final hardness of the material. After the aging process, the material is cut to the final length and any final fabrication (holes, pockets, or other secondary machining) can be done. Extruded heat sinks are usually supplied with a “finish” such as anodizing, which can enhance its thermal performance. The heat sinks can also be supplied with a chromate finish which provides some corrosion protection or can be used as a primer before a final paint or powder coating is applied. While each extruded shape is unique to the requirements that it was designed for, extruded heat sinks are the most cost-effective cooling solution. Each shape is engineered to achieve optimal thermal and structural performance. Wakefield Thermal partners with a large list of vendors that ensure that you have the best thermal solution based on your system structure and thermal requirements.