Mounting instructions SKiM - Semikron

Basic comments on baseplateless module design

In standard modules with baseplates, the geometry of the

interface between the module case and heat sink is only

controlled by the shape of the baseplate. Therefore,

modules with baseplates are specified with a convex

baseplate curvature to allow for a good thermal contact

when mounted.

The concept of baseplateless design is to achieve a good

thermal contact in the active area of the DCB-substrate

close to the dies by an implemented pressure contact

system (SKiiP technology). This pressure contact system

is activated by mounting the module onto the heat sink.

During this process, the spring contact system is activated

and assures a close contact between the heat sink and the

module.

The integrated pressure contact system does not require

a pre-shaped module base. Therefore, the specification

limits for the base geometry of an unmounted module are

more than for baseplate modules.

Mounting instructions SKiM®

Preliminary

Bottom view of a SKiM 4

module, mounted on a

transparent heat sink. The

evenly distributed thermal

grease layer shows the

homogeneous pressure

distribution.

SKiiP technology

constant distance

constant pressure

on the DCB

SKiM®

1.2 ESD protection

SKiM 4/5 modules are sensitive to electrostatic charges. All SKiM modules are ESD protected during

transport, storage and mounting process with an ESD cover. When unpacking the module and during

assembly use conductive grounded wristlet and a conductive grounded working place.

1.3 Sectional drawings of SkiM 4 , SkiM 5

Interface drawings for mechanical design are available in PDF-format. PDF – files are available in the

internet: http://www.semikron.com/products/skim_.html

2 Module assembly

2.1 Heat sink specification

To obtain the maximum thermal conductivity of the module, the mounting area on the heat sink must be

clean and free of grease and particles. The mechanical specification of the mounting area is:

Flatness: 50 µm per 100 mm

Roughness Rz : 6,3 µm

Machined without overlaps

2.2 Specification for bottom surface of module

The mounting surface of SKiM modules must be free from grease and particles.

Due to the manufacturing process of the DBC substrate, the bottom side of the SKiM might show

scratches, holes or similar marks. The following figures (Fig 3.1 – Fig 3.3) define surface

characteristics, which do not affect the thermal conduction behaviour.

Reworked bottom surfaces (Fig. 3.4) have to comply with the surface specification according to Fig.

3.1 – Fig. 3.3

Fingerprints do not affect the thermal behaviour.

Fig. 3.1: Scratches on the SKiM bottom surface.

Fig. 3.2: Etching hole (hole down to substrate level ) in the SKiM bottom surface

300 µm

10 µm

600 µm

= 300 µm

1.0 mm

SKiM®

Fig. 3.3: Etching holes (hole not down to substrate level) in the SKiM bottom surface

Fig. 3.4: SKiM bottom surface after rework

2.3 Application of thermal grease

To avoid air gaps at the interface between the module and the heat sink a layer of thermal grease

must be applied. The function of the grease is to flow according to the shape of the interface, allowing

a metal-to-metal contact where it is possible and filling the remaining gaps. Recommended thermal

grease material is Wacker-Chemie P 12.

The thermal grease can be applied either to the base area of the module or to the mounting area of the

heat sink. A hard rubber roller or a screen print (mesh-size 43T) is recommended for an even

distribution of the grease.

The thickness of the applied grease layer should be 40 - 60 µm. It can be checked by a measuring

gauge (e.g. Fa. ELCOMETER Instruments GmbH, Himmlingstr. 18, 73434 Aalen, Tel. +49-7366-

919283: Sechseck-Kamm 5 - 150 µm).

2.4 Mounting of the module

After applying the thermal grease, the SKiM 4 or SKiM 5 is placed on the heat sink. The mounting

screws are inserted and evenly tightened by hand (approx. 0.5 Nm) and afterwards tightened to the

final torque (ref. table 3.1) in the sequence shown in Fig. 3.5 (SKiM 4) or Fig 3.6 (SKiM 5). Torque

wrenches with automatic release are strongly recommended. Subsequent tightening of the screws is

not allowed.

< 250 µm

2.0 mm

SKiM®

The minimum torque already establishes the specified thermal contact. A further increase of the

maximum mounting torque will not improve the thermal contact.

Screw Torque

Module

Washer

min. max.

unit

SKiM 4 M5 M5 – ISO 7092 2 3 Nm

SKiM 5 M5 M5 – ISO 7092 2 3 Nm

Table 3.1: Torque specification for heat sink fixing

Fig. 3.5: Torquing sequence SKiM 4

Fig. 3.6: Torquing sequence SKiM 5

Torque

Module Screw

min. Max.

unit

SKiM 4 M6 4 5 Nm

SKiM 5 M6 4 5 Nm

Table 3.2: Torque specification for terminals

The maximum immersion depth of the screws for SkiM 4 and SkiM 5 may not exceed 9 mm.

8513

6742

SKiM®

2.5 Mounting of DC bus bars

The functionality of the pressure contact system can be disturbed by too high pulling forces on main

terminals, resulting in malfunction of the module.

For the maximum allowed pulling forces per terminal on SKiM 4 and SKiM 5 modules refer to table 3.4.

and Fig. 3.7

Force: Maximum allowed force Remark

FX < 100 N -

FY < 100 N -

F+Z < 100 N only for short time during

mounting

F-Z < 500 N -

Table 3.4: Maximum allowed pulling forces per terminal

Fig. 3.7: Maximum allowed pulling forces

In order to reduce pulling forces, dc link bus-bar and cables may be fixed by additional posts (Fig. 3.8)

Fig. 3.8 : Recommended dc-bus bar assembly

dc bus bar / ac terminals

heat sink

fixing post

SKiM®

3 Driver- Assembly

For SKiM 4 and SKiM 5 the following IGBT-gate drivers with protection functions (for details refer to

chapter SEMIDRIVER) are available:

Module Types IGBT Driver

SKiM 4 all SKHI 64

SKiM 5 all SKHI 65

Table 3.5: Available SKiM SEMIKRON gate driver

The SEMIDRIVER or other driver printed circuit boards (PCBs) can easily be snapped onto the SKiM

module. Lateral movements of the driver PCB during mounting are not allowed to avoid damage of the

spring contacts. It is recommended to use guiding pins temporarily located in the posts as shown in

Figure 3.9 (pins can be ordered by SEMIKRON).

Fig. 3.9: SKiM module with guiding pins

Fig. 3.10: Alignment of the PCB on the SKiM module and assembly.

SKiM®

For mounting the PCB on the SKiM module all snappers have to be snapped in according to Fig. 3.11.

The guiding pins then have to be removed and the PCB has to be fixed by self tapping screws EJOT

PT K30x8 WN 1452 (the details of screw head design can be chosen by the customer).

Fig. 3.11: Final assembly of driver PCB .

Table 3.6 specifies the minimum and maximum torque values for the PCB mounting screws. The

usage of torque wrenches with automatic release is strongly recommended. Subsequent tightening of

the screws is not allowed.

Module Screw Value Unit

min. Max.

SKiM 4 PT K...30x8 0,9 1,1 Nm

SKiM 5 PT K...30x8 0,9 1,1 Nm

Table 3.6: mounting torque for PCB mounting screws

Recommended screws may be supplied by EJOT Verbindungstechnik GmbH, http://www.ejot.de,

info@ejot.de.

Click !!

Holes for

screws