Guy, Thanks for the input. We use torque specifications relative to the screw diameter and these seem to dovetail with the device manufacturer's specs. In several applications we use either "snap-in" clips or "screw-down" clips. These are on our larger extruded heat sinks. The stamped small fin heat sinks is where we mostly use the thermal grease. Phil -----Original Message----- From: Guy Ramsey [mailto:[log in to unmask]] Sent: Monday, August 20, 2001 10:10 AM To: [log in to unmask] Subject: Re: [TN] Thermal Compound considerations I have been out of this loop for a couple of years but as I recall the grease / mica combination has (potentially) the best themal transfer characteristics. But is clearly an assembly problem. The TO 220 package will have a torque specification, to achieve best transfer without bending the tab. Another solution is spring clips that press down on the package. These work well with either the pads or the grease. We found them to provide the best mechanical interface to the heatsink. They also eliminated the need for a torque wrench in assembly. How much grease? Just enough grease to fill the gaps without viods, a very thin layer. Guy Ramsey Senior Lab Technician / Instructor E-Mail: [log in to unmask] <mailto:[log in to unmask]> Ph: (610) 362-1200 x107 Fax: (610) 362-1290 -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Phil Nutting Sent: Monday, August 20, 2001 9:43 AM To: [log in to unmask] Subject: [TN] Thermal Compound considerations Here is this morning's question(s). I posted a note last week about using the old style thermal grease. I agree with your comments about using some of the new Berquist or Power Devices insulator pads, some of which we currently use. Today I am looking for some of your thoughts on an alternate style material (grease "replacement"). There are several products on the market which are phase change (at 60°C/140°F) thixotropic, non-silicon products which prevent run out (oozing out from under the device) at operating temperature. Now assuming we use this material on TO-220 packages and mount the device with the standard mounting hole in the tab the device tends to not sit completely flat on the heat sink (This is a problem not associated with the thermal compound but the mechanical design of the device). On concern brought to my attention is water trapped under the device. And our intent is to solder these devices to the PWB (through hole) and de-flux (OA flux) the boards after assembly in a batch DI wash with no saponifiers. Do any of you see this as an issue? We presently use the old style thermal grease in this manner mostly with TO-220 devices and heat sinks which are the same size as the body. If our DI wash is running at 120°F and the wash chamber is set for 135°F are there any significant issues with approaching the phase change point that will degrade the thermal compound's operational characteristics? We may end up using one of the pad style items, but I wanted to tap into your collective wisdom to help with the end decision. This manual application tends to be messy, time consuming and different by each assembler. Thanks in advance. Phil Nutting ------------------------------------------------------------------------ ---- ----- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ------------------------------------------------------------------------ ---- ----- ------------------------------------------------------------------------ --------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ------------------------------------------------------------------------ --------- --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------