Mounting recommendations for M174, M177 and M244

AN2027

2/5

Doc ID 10738 Rev 2

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 printed-

circuit 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

Description

Flange

Leadframe

Ceramic

insulator

Plating

Torque

(Nm)

Leads

Flange

Min.

Max.

M174

0.500 DIA 4L

non herm

w/flange

Cu

ALLOY 42

(Fe58 /

Ni42)

BeO

(99.5%

min)

Au (100µ min)

over Ni (100µ

min / 350µ max)

Ni (100µ min) +

Pd (10µ min)

0.6

0.75

M174

(Moly disk)

0.500 DIA 4L

non herm

w/flange

(moly disk

Cu-Mo-Cu

ALLOY 42

(Fe58 /

Ni42)

BeO

(99.5%

min)

Au (100µ min)

over Ni (100µ

min / 350µ max)

Ni (100µ min) +

Pd (10µ min)

0.6

0.75