This work concerns the development of an innovative processing route to manufacture a new design of ceramics micro-heat exchanger. The manufacture is based principally on the Ceramic Injection Moulding process of the different elements of the micro-heat exchanger. Furthermore, the different elements are cofired in order to provide directly the part. The micro heat exchanger is characterised by a complex network of inner channels. The paper focuses on the alumina feedstock based on ultrafine alumina powders and on the conditions of injection, debinding and co-firing, developed essentially for this study. Moreover, the interfaces between the co-fired elements have been characterized by optical microscopy. This process may be applied to design complex and precise microstructures for mass produced micro heat exchangers, cold plates and micro reactors than can be used for various large scale applications in the field of energy and electronic cooling

BROCHARD, Jean-Alain

FEDERZONI, Luc

GRUSS, Jean-Antoine

I-Revues

18ème Congrès Français de Mécanique Grenoble, 27-31 août 2007 
1 
Alumina micro-heat exchanger manufactured by Ceramic Injection 
Moulding 
Luc Federzoni, Jean-Antoine Gruss, Jean-Alain Brochard 
CEA/LITEN Grenoble 
CEA/LITEN Grenoble, 17 rue des Martyrs, F-38054 Grenoble cedex 9 
luc.federzoni@cea.fr 
 
 
 
 
Résumé : 
Le travail concerne le développement d’un nouveau procédé de fabrication d’un échangeur thermique en 
céramique. Le procédé s’appuie sur le procédé de Ceramic Injection Molding (CIM), qui permet la 
réalisation des éléments constitutifs de l’échangeur. Ensuite les différents éléments sont assemblés par 
co-frittage. L’échangeur est caractérisé par un réseau interne de canaux enterrés. 
Le papier décrit le mode de développement d’un feedstock d’alumine basé sur des poudres ultrafines et 
décrit les conditions, d’injection, de déliantage et de co- frittage des éléments. L’interface entre les 
éléments a été caractérisée par microscopie optique.  
Le procédé pourrait être utilisé pour fabriquer des micro-échangeurs thermiques à bas coût de forme 
complexe dans des domaines variés comme l’énergie ou le refroidissement de l’électronique. 
  
 
Abstract : 
This work concerns the development of an innovative processing route to manufacture a new design of 
ceramics micro-heat exchanger. 
The manufacture is based principally on the Ceramic Injection Moulding process of the different elements 
of the micro-heat exchanger. Furthermore, the different elements are cofired in order to provide directly 
the part. The micro heat exchanger is characterised by a complex network of inner channels. 
The paper focuses on the alumina feedstock based on ultrafine alumina powders and on the conditions of 
injection, debinding and co-firing, developed essentially for this study. Moreover, the interfaces between 
the co-fired elements have been characterized by optical microscopy.  
This process may be applied to design complex and precise microstructures for mass produced micro 
heat exchangers, cold plates and micro reactors than can be used for various large scale applications in 
the field of energy and electronic cooling. 
 
Mots-clefs :  
 
microPIM ; heat exchanger ; alumina 
 
1 Introduction 
 
Micro powder injection moulding (or micro-PIM) is a technique which has been largely developed 
in recent studies [1-9]. This technique can be used for manufacturing micro parts for large-scale 
production. This process allows also the replication of very fine details, typically in the order of 
magnitude of the size of the powder. However, the development of feedstock for micro-PIM with 
nanopowders is difficult as the viscosity of the feedstock then increases drastically [2]. The majority of 
feedstocks for microPIM are therefore composed of micrometer size powder. They allow replicating 
details of a few 10th micrometers [1].  
 
Among several applications, micro heat exchangers and micro reactors appear to be an important 
issue for the micro-PIM. Several demonstrators have been manufactured by several authors [10, 11], until 
now.  
  
In this research work, we have developed a process chain to produce a micro heat exchanger. The 
different processing steps concern: 
18ème Congrès Français de Mécanique Grenoble, 27-31 août 2007 
2 
 
- the development of feedstock with ultrafine powders of alumina 
 
Due to the thinness of the inner channel patterns, it is required to use ultrafine powder to allow the 
replication of such a fine details. A new kind of feedstock was developed, based on the blending of 
bimodal spherical populations of powders, 
 
- the injection, debinding and co-sintering of the plates 
 
The quality of the interface between the former plates has been characterized by optical microscopy.  
 
In this paper, we describe the different processing stages for the fabrication of a multi-layer micro 
heat exchanger. This heat exchanger presents several originalities: 
- it is made on pure alumina,  
- it embeds a complex inner channel network. 
- it is assembled directly by co-firing: the different plates are assembled with the help of tapes 
inserted between plates. 
 
2 Experimental 
 
Ceramics powder 
In this study, we have used two different kinds of ceramic powders, called powder A and B provided by 
the French company Baikowski. Table 1 and 2 show some characteristics of these powders.  
The powders chosen are specific for the injection process and their particle sizes were chosen in order to 
obtain high solid content for the feedstock. 
 
Powder A : alumina 
D50 (µm) 0,33 
 Powder B : alumina 
 D50 (µm) 0,18 
Table 1: Size of the powders used in this study. 
 
Binder system 
A blend of polypropylene, (86.6 wt%), and paraffin wax (8.6% wt%) was used. A small amount (4.8 wt 
%) of stearic acid was added to the polymer blend in order to improve the powder dispersion 
 
Injection of the plates 
A Battenfeld 250 plus press has been used to inject the parts.  
 
Debinding cycle 
In this study, we have made only thermal debinding cycle. This cycle was performed at 550°C for 3 
hours. After completion of the debinding cycle, it was checked that there were no residual organic 
material.  
 
Bonding tapes  
In order to permit the assembly of plates during co-firing, we have used some home-made tapes 
constituted of nanosized alumina powder (10nm) with a matrix of polystyrene. These tapes have been 
inserted between the plates, just before co-firing. The thickness of the tapes is around 100 microns. 
During the sintering cycle, the tapes are debinded and the nanopowder on the tapes are sintered 
simultaneously with the plates.  
 
Sintering cycle  
The sintering cycle consisted in a cycle at 1700°C during 3 hours under air. 
 
 
 
18ème Congrès Français de Mécanique Grenoble, 27-31 août 2007 
3 
3 Results  
In this study we have set up the complete process chain from the powder to the heat exchanger. The 
complete chain is described in figure 1. 
 
 
 
Polymer 
Alumina 
powder 
Melting Grinding 
Injection Green part 
Debinding Stratified assembly with home 
made ultrafine alumina ribbon 
Feedstock 
Co-firing 
Multi plates’ exchanger 
 
Figure 1: Sketch of fabrication of the heat exchanger.  
Feedstock preparation  
In this study, we have mixed several types of alumina with different particle sizes (see table 1) in order to 
increase the solids content within the feedstock. With this methodology, it was possible to reach 67% of 
solid content even the average particle size of the powder was quite small. Table 2 displays the 
composition of the feedstock developed for this study.  
 
 
Materials 
Volumic weight 
(g/cm
3
) Massic % Volumic % 
Powder A 3,96 11 8 
Powder B 3,96 78 58 
PP 0,9 9 30 
PW 1,03 0,9 2,6 
AS 0,94 0,5 1,6 
Table 2: Compositions of the feedstock optimized. 
18ème Congrès Français de Mécanique Grenoble, 27-31 août 2007 
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Injection of the part  
A typical micro heat exchanger has been designed in order to produce it by overlapping of identical plates 
as illustrated in figure 2. 
 
 
 
Figure 2: Structure of the heat exchanger.  
 
Each plate has 30 microchannels (500 µm width and 500 µm depth). Inlet and outlet headers were not 
optimized for even distribution through the channels. 
On the figure 2, we can notice that between 2 successive plates, we impose a rotation of 180°.  
 
Debinding tests were made on four samples. Results are shown in table 3. Parts are fully dense, without 
cracks and have undergone isotropic shrinkage. The binder removal is 100%. 
 
 
  
 Weight (g) results 
sample green parts brown parts wt lost (%) Binder removal (%) 
1 7,28 6,51 10,6 100 
2 5,14 4,59 10,7 100 
3 6,32 5,64 10,7 100 
4 4,82 4,30 10,7 100 
Table 3: Binder removal at debinding stage 
18ème Congrès Français de Mécanique Grenoble, 27-31 août 2007 
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Co-firing results  
 
Figure 3: final part 
 
 
One ribbon has been inserted between each plate (see figure 1) before co-firing in order to assist the 
joining of the plates. The stack has been sintered with an applied load (1 kg) on the top surface. After 
sintering, no cracks or geometry distortion did appear. The ribbon has been correctly debinded. Density 
measurements made by Archimedes method gave an average value of 95% of relative density for the final 
part. A 4 plate parts is displayed in figure 3. 
 
Characterization of the interface between the plates after co-firing 
 
A second heat exchanger has been made and sawed in order to observe the interface by optical 
microscopy. Figure 4 allows us to assess he interface observed by means of optical microscope. The 
contact between two plates is quite good. 
 
 
 
Figure 4: Optical microscopy of the interface between 2 plates at different magnifications. 
 
18ème Congrès Français de Mécanique Grenoble, 27-31 août 2007 
6 
After sintering the remaining thickness of the former tape can be seen at the higher magnification (bottom 
image of figure 4). It is estimated at 75 microns. We observe that the interface region is clearly crack-free.  
 
4 Conclusions 
A new process chain has been developed in order to manufacture complex-shape 3D parts like heat 
exchangers or micro reactors. This process is based on the micro Powder Injection Molding process. We 
have developed a feedstock based on a blend of ultrafine alumina powders. The optimization of the binder 
system and the proportion of the two different types of powders has led to the possibility to make a 
feedstock with a high solids content (66 vol %) and good injectability. 
 
To get a good interface between the plates, a specially designed tape, made essentially of a mixture of 
nanometric alumina powders and polymers was developed. This tape is inserted between the plates just 
before sintering in order to insure a good assembly between the plates.  
Optical observations have confirmed the good cohesion between the plates. No cracks have been 
observed.  
 
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Heat exchanger manufactured by Ceramic Injection Moulding

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