[Elecraft] Purpose of Thermal Pad on Output Transistors

Sun Mar 28 11:40:01 2004

Hi

If you a asking about the pads on the K2 finals they insulate the =
collector from grounding on the bottom of the case and the silicone =
material transfers the heat from the transistor to the bottom of the =
case. If you are asking about the pads in the KPA100 then transferring =
the heat is the only function. The problem of not using the pads is at =
the level of machining used in the transistor and the heatsink there =
will always be high and low spots on the two surfaces. The pads fill in =
the spaces and form a better contact. The silicone rubber on the pads =
have a very good heat transfer characteristic. Silicone grease was used =
for this purpose at one time but it is messy and tends to get into =
places where you don't want it. It also tends to dry out or evaporate =
over a long time (several years) and the heat transfer properties =
reduce. The pads are easy to install and do not dry out. Without the =
pads the heat may build up in the transistor case because it cannot =
transfer to the heatsink. If the junction in the transistor is allowed =
to get hot enough it will damage the transistor or may even destroy the =
transistor.

Don Brown
KD5NDB
  ----- Original Message -----=20
  From: [email protected]<mailto:[email protected]>=20
  To: [email protected]<mailto:[email protected]>=20
  Sent: Sunday, March 28, 2004 10:03 AM
  Subject: [Elecraft] Purpose of Thermal Pad on Output Transistors

  What is the purpose of the thermal pad that goes between the final=20
  transistors & the heat sink?  (According to the manual, the transistor =

  will burn up in short time w/o this pad)

  73, Lynn, K5AVJ
  K2 #1411

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