You have to lap the heat sink on the brick flat for impedence reasons. You still have to use heat sink compound to fill the gaps for thermal transfer reasons. It would also be nice to perfect the surface on the recycled Mastr II or Micor chassis to 50 um smoothness, but that would require a machine shop.
The Science Behind It: http://www.downeastmicrowave.com/PDF/MOSFET%20PA_pdf.PDF The Power brick can be resurfaced by hand with sand paper and a piece of glass, I have done it, but I got metal poisoning for not wearing gloves or a dust mask. If any has ever owned a Yaesu FT-5100 or any radio that uses a SAV-27 brick, they will understand the importance of having smooth and even surfaces when the substrate cracks in the brick and the module needs resoldering. On 7/16/07, Ron Wright <[EMAIL PROTECTED]> wrote: > To achieve a good heat sink coupling/bonding of 2 surfaces this is what heat > sink compound is for. Just having a smooth surface does not insure a good > bond between 2 surfaces due to different flatness/shape. > > I wonder in any Mitsubishi power bricks mounting instructions what they > recommend. Is its surface being used for any RF connection. I hope not, not > good engineering. > > 73, ron, n9ee/r > > > > > >From: DCFluX <[EMAIL PROTECTED]> > >Date: 2007/07/16 Mon AM 12:12:13 CDT > >To: [email protected] > >Subject: Re: [Repeater-Builder] Re: 224 MHz PA fun and war stories > > > > >Gentleman, > > > >A word of caution with the new Mitsubishi power bricks. Please be sure > >to lap the bottom side of the brick flat using a belt sander with 150 > >grit and followed with 400 grit sand paper to achieve optimum > >smoothness. > > > >No one is sure what they were thinking with the bottom side of the > >module on the latest generation of bricks, but unless the heat sink > >contact is in the 100% range, you risk blowing up the module due to a > >ground and a heat resistance problem. > > > > > Ron Wright, N9EE > 727-376-6575 > MICRO COMPUTER CONCEPTS > Owner 146.64 repeater Tampa Bay, FL > No tone, all are welcome. > > > > > > > > Yahoo! Groups Links > > > >
