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9781467322409/12/$31.00 2012 IEEE 161 35th Int. Spring Seminar on Electronics Technology

Electron Beam Welding of MicroHousings with Dissimilar Metals for

Electronic Circuits

M. Steinhauser, C. Krbs, R. Bauer

University of Applied Sciences Dresden, Hochschule fr Technik und Wirtschaft (HTW),

Faculty of Engineering, Dresden, Germany

[email protected]

Abstract: The Electron beam technology with its electromagnetic lenses enable the inertialesslydeflection and focusing of the beam and gives a lot of possibilities for welding and modification ofdifferent materials. This paper and the poster shows selected results of research investigations onthermal electron beam processes of HTW Dresden. The first part handles with the influences of theheat-input in the weld zone. The second part shows results of investigations to weld 16 electronic-housings at the same time by using the fast beam deflection as multi-weld technology.

1. INTRODUCTION

In times of energy efficiency are the economical

use of resources and the substitution of strategic

materials one of the important goals for research

investigations. New combinations of conductor- and

lightweight materials are increasingly interesting for

electrical-, automobile, medicine- and aviation

industry [1].

One strategy to reach these goals is the

combination of dissimilar metals to get the right

characteristics in the respective area. With the most

state of the art welding technologies this joints are not

producible in the required quality standard. Theelectron beam with its inimitable properties

accommodates great procedural advantages in this

section.

2. HEAT INPUT OF ELECTRON BEAM WELDING

The need for miniaturisation of electrical andelectronic assemblies leads in high requirements for

welding technology. Especially the space between

housing and the electronic circuit shows great

potentials for optimizing [2]. With a lower heat input

by the welding process the gap between housing and

electric circuit can be reduced to a minimum, so the

size of the housing can be considerably smaller.

To measure and characterise the chronological

sequence and the peak temperatures by welding with

the electron beam some basic experiments have been

made. In figure 1 you see the experimental setup of

the tests. For a plate thickness of 1 mm a 2-Dimensional thermal conduction may be adopted.

Fig. 1. Experimental setup for heat measurements.

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Fig. 2. Heat input as function of time and distance for

different materials.

The different thermal conductance of the materials

leads to diverging temperatures in the near of the

weld. This is the important criterion for the spacebetween housing and electrical circle.

The next topic presents selected results of welding

experiments at HTW Dresden.

For a plate thickness of 1 mm a 2-Dimensional

thermal conduction may be adopted, but for higher

thickness another experimental setup is needed.

3. ELECTRON BEAM WELDING OF HOUSINGSTYPE TO39

One of the great advantages of the electron-beam-technology is the inertialessly deflection and focusing

of the beam. This feature enables special joining

strategies which cannot be achieved by conventionally

welding processes [1] (Figure 3).

In the following chapter this will be shown on the

example of welding a vacuum-closed TO39-Housing.

Fig. 3. Multi process electron beam technologies.

The solution of this task made in several process

stages. At the first step the weld will be generated by

affect the housing in a circle with the CNC-

Manipulator under the idle electron beam. Theproblem of this solution is the uneven shrinking of the

hot weld, which leads into weld imperfections like

gaps, gas pores and cracks and also into long weld

intervals.

One way to solve this problem is the use of the fast

beam deflection. With electromagnetic lenses the

beam will deflect between three different points of the

housing. With modulation of the dwell time at thepoints three simultaneous weld baths can be created.

With a continuous geometrical displacement of the

coordinates of the points a closed weld seam will begenerated (Figure 4 left picture). The complete weld

process take part in one second, the weld intervals are

minimized.

An alternative by using the fast beam deflection is

the combination with the CNC-Maniplulator of the

electron beam facility. The beam deflection create

simultaneous 16 different weld baths on 16 housings,

the CNC Manipulator affect the housing in a circle

function (Figure 4 right picture).

Fig. 4. 3 beam technology (l.);12 beam technology (r.).

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A further aim is the weld of the 16 housings at thesame time in combination with the named three weld

bath strategy. For this investigation a huge

programming effort for the fast beam deflection is

needed. First trials have shown some problems with

an overshooting of the deflection amplifiers in cause

of the high deflection speed and the electromagneticinertia of the commonly used deflection-amplifier. At

the moment the latest deflection amplifiers on market

will be installed on the HTW E-beam facility. With

this new technology the problems will be solved.

4. WELDING OF DISSIMILARMETALS

One of the great advantages of the electron beamtechnology is the inertialessly deflection of the beam

by using electromagnetical fields. With this

technology open up new welding fields for the joining

of dissimilar metals like Titan-Aluminum, Steel-Aluminum or Copper-Aluminum. This material-

combinations offers new improved properties for

lightweight constructions, electrical contacting or

corrosion resistance by simultaneously reduced

production costs.

In course of the high prices of copper on market it

is planed to substitute this material with aluminum.

This courses in losses by the electrical resistance but

there is a great potential by reducing the vehicle mass.

A weak point of aluminum is the bad accessibility on

copper.The different position in the PSE leads into a lot of

different material properties, which are negative effect

the joining process and the fatique resistance. One

alternative to join this material combination is the

electron beam welding.

The possibility to deflect the beam with very high

frequenzies and the Joining in the high vacuum paving

the way to the creation of new and innovative process

technologies to affect the weld bath, which arte not

reachable by the common joining technologies. At the

electron beam laboratory of HTW Dresden somesuccessfully trials are made. The focus of this Project

lays on the specific investigations to innovative

electron beam joining technologies, the metallurgical

and mechanical behavior of the joining, the

metallurgical preparation and the long time stability.

The main goal is to reach strength conditions in the

welding zone in relation to aluminum.

First trials to join the two materials by welding

leads into not satisfactory results. The forming of

intermetallic phases induce into low mechanical

strength properties. The joint, a macrograph and a

REM-Picture are shown in figure 5 and 6.

Fig. 5. Electron beam weld of copper and aluminium.

Al 99,5 Cu-DHP

WEZ Al

1 mm

Mischzone

Al 99,5 Cu-DHP

WEZ Al

1 mm

Mischzone

Al 99,5Al 99,5 Cu-DHPCu-DHP

WEZ AlWEZ Al

1 mm1 mm

MischzoneMischzone

Fig. 6. Macrograph of the joint (l.);REM Picture (r.).

A new and innovative way to join this different

materials is the application of new electron beam

technologys (Fig. 3). By using one of the shown

Multi-process technologies a joining with a good

mechanical behaviour is created. With a combination

of the advantages of welding and brazing thethickness of the intermetallic phases is reduced up to

10 micron.

Fig. 7. Micrograph of the innovative Cu-Al-Joint.

REFERENCES

[1] Schiller, Heisig, Panzer: Elektronenstrahltechnik,Verlag Technik Berlin, 1995.

[2] Krbs, Schulze: Trends und Entwicklungen in derElektronenstrahltechnik, Vortrag zum 2. Tag derForschung, HTW Dresden 2011.

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