BERGQUIST® HI FLOW THF 1000F-AC

ASTM classifies a phase change as a Type 1, viscous liquid that exhibits unlimited deformation when a stress is applied. Henkel uses test equipment that is designed to meet ASTM D5470 specifications for Type 1, which requires a shim or mechanical stop to precisely control the thickness. The phase change material is conditioned at 5°C over the stated phase change temperature. Understanding that time is also a key variable for material flow, the over-temperature condition is limited to 10 minutes and then allowed to cool, prior to initiating the actual test at the given pressure. The 10-minute time has been demonstrated to be an acceptable time period for the thermal mass inherent in the test setup. Note: Actual application testing may require more or less time to condition, depending upon the heat transfer and associated thermal mass. The performance values are recorded and published at 10, 25, 50, 100 and 200 psi to give the designer a broad-based understanding of HI-FLOW material’s performance.

Avoid using HI-FLOW in applications in which the device will not reach operation at or above phase change temperature. Also avoid applications in which the operating temperature exceeds the maximum recommended operating temperature of the compound.

The 65°C phase change temperature was selected for two reasons. First, it was a low enough temperature for the phase change to occur in applications. Second, it would not phase change in transport. Studies show that shipping containers can reach 60°C in domestic and international shipments. The higher phase change temperature eliminates the possibility of a product being ruined in shipment. We offer a standard line of BERGQUIST® HI-FLOW THF 1000, BERGQUIST® HI-FLOW THF 700 and BERGQUIST® HI-FLOW THF 1600 series products with 55°C phase change for those customers wanting the lower phase change temperature.

Upon achieving phase change temperature (e.g., preconditioning), Henkel has demonstrated that 10 psi provides adequate pressure to achieve exceptional thermal performance. Henkel continues to research lower pressure wet-out characteristics in an effort to minimize interfacial losses associated with ultra-thin material interfaces.

Mechanical fasteners are required. Henkel recommends the use of spring clips to maintain consistent pressure over time

HI-FLOW works best with a clip or spring washer-mountedassembly. The continuous force applied by these devicesallows the HI-FLOW material to flow and reduce the crosssectional gap. Henkel suggests that design engineers evaluatewhether a screw-mount assembly will have acceptableperformance. See TO-220 Technical Note.

The adhesive in the current construction does adhere moreto the heat sink aluminum than to the HI-FLOW material.There is the potential that the adhesive will be removed bythe heat sink surface when it is removed to reposition onthe heat sink. Time and/or pressure will increase the bond tothe aluminum, increasing the potential for the adhesive toadhere to the heat sink.

Standard electronics industry cleaning procedures apply. Remove dirt or other debris. Best results are attained when the HI-FLOW material is applied to a heat sink at a temperature of 25°C ± 10°C. If the heat sink has been surface treated (e.g., anodized or chromated), it is typically ready for assembly. For bare aluminum, mild soap and water wash cleaning processes are typically used to eliminate machine oils and debris.

If the material has not gone through phase change, the material will readily release from the device surface. For this situation, the HI-FLOW material will not likely have to be replaced. If the material has gone through the phase change, it will adhere very well to both surfaces. In this case, Henkel suggests warming the heat sink to soften the HI-FLOW compound for easier removal from the processor. Replace with a new piece of HI-FLOW material.

Insulated HI-FLOW products are manufactured with inner film support. This film stiffens the material, allowing parts to be more readily die-cut as well as making the material easier to handle in manual or automated assembly.

Many HI-FLOW materials have no surface tack at room temperature. The softer materials will pick up dirt more readily. Softer resins are more difficult to clean if any dirt is on the surface. If you try to rub the dirt away, the dirt is easily pushed into the soft phase change materials. HI-FLOW coatings are typically hard at room temperature rendering them easier to clean off without embedding dirt.