ST AN2027 APPLICATION NOTE
AN2027
Application note
Mounting recommendations for ceramic DMOS packages
Introduction
This application note provides mounting recommendations for ceramic packages used in the
assembly of DMOS radio frequency transistors suitable for applications such as ISM and FM
broadcasting.
June 2011 Doc ID 10738 Rev 2 1/5
www.st.com
Mounting recommendations for M174, M177 and M244 AN2027
1 Mounting recommendations for M174, M177 and
M244
1.1 Mounting recommendations
● Ensure holes in heatsinks are free from burrs
● Minimum depth of tapped holes in heatsinks is 6 mm
● Use 4-40 UNC-2A cheese-head screws with a flat washer to spread the joint pressure
● The minimum flatness of the mounting area is 0.02 mm
● Mounting area roughness should be less than 0.5 µm (micro)
● Avoid, as much as possible, use of flux or flux solutions because flux can penetrate
even when hermetically sealed ceramic-capped transistors. Tin and wash the printedcircuit board BEFORE mounting the power transistors, then solder the transistor leads
without using flux
● Transistor leads may be tinned by dipping them full-length into a solder bath at a
temperature of about 230°C. No flux should be used during tinning
● Recommended heatsink compounds : WPSII (silicon free) from Austerlitz Electronics,
340 from Dow Corning etc.
1.2 Mounting sequence
● Apply a thin layer of evenly distributed heatsink compound to the flange
● Position the device with flat washers in place
● Tighten the screws until finger tight (0.05 Nm)
● Further tighten the screws until the specified torque is reached
● For M174, M177 & M244 type of packages, torque should be minimum 0.6 Nm and
0.75 Nm max.
Table 1. DMOS packages - list of materials
Package
type
M174
M174
(Moly disk)
Description Flange Leadframe
0.500 DIA 4L
non herm
w/flange
0.500 DIA 4L
non herm
w/flange
(moly disk
Cu
Cu-Mo-Cu
ALLOY 42
(Fe58 /
Ni42)
ALLOY 42
(Fe58 /
Ni42)
Ceramic
insulator
BeO
(99.5%
min)
BeO
(99.5%
min)
Plating
Leads Flange Min. Max.
Au (100µ min)
over Ni (100µ
min / 350µ max)
Au (100µ min)
over Ni (100µ
min / 350µ max)
Ni (100µ min) +
Pd (10µ min)
Ni (100µ min) +
Pd (10µ min)
Torque
(Nm)
0.6 0.75
0.6 0.75
2/5 Doc ID 10738 Rev 2
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