PROCESS OF ENCAPSULATING ELECTRONIC COMPONENTS

Abstract

In order to carry out the encapsulation of electronic components, the invention proposes to cover the electronic components (7) with a heat-polymerisable material corresponding to a composition comprising a diimide constituent and a diamine constituent, in which the diimide constituent has been predissolved in the diamine constituent, and to heat the assembly obtained under conditions suitable for carrying out the curing of the material by an addition polymerisation reaction between said diimide constituent and the diamine constituent. The invention finds an application in particular in the field of electronic power modules.

6

Claims

1. Process for encapsulating electronic components, comprising the stages of: encapsulating the electronic components in a heat-polymerisable material corresponding to a composition comprising a diimide constituent and a diamine constituent, in which the diimide constituent has been pre-dissolved in the diamine constituent, said dissolving of the diimide in diamine being carried out at ordinary temperature and said components being previously placed, together with the associated connection circuits, in a housing which is filled by said material in the liquid state, and heating the assembly obtained under conditions suitable for carrying out the curing of said material by an addition polymerisation reaction between said diimide constituent and said diamine constituent.

2. Process according to claim 1, wherein the curing of the material is carried out at a temperature ranging between 80° C. and 200° C.

3. Process according to claim 2, wherein the curing duration is under one hour.

4. Process according to claim 1, wherein said diimide constituent is a dimaleimide, maleimide, nadimide or allyl-nadimide.

5. Process according to claim 4, wherein said diimide is a composition comprising at least two maleimide groups at the ends of an aromatic chain, in particular a benzene chain, such as 1.3 or 1.4 di(maleimido) benzene, or naphthalene 1.5-dimaleimide, or (bis)-maleimide.

6. Process according to claim 4, wherein said diimide is a composition comprising at least two maleimide groups at the ends of an aliphatic chain of low molecular weight, such as in particular 1.4 di(maleimido) butane or tris(2-maleimido-ethyl) amine.

7. Process according to claim 1, wherein the diamine constituent is based on an aliphatic diamine, advantageously supplemented by an aromatic diamine or a silicone diamine.

8. Process according to claim 1, applied to encapsulate electronic components in a power module housing.

9. Process according to claim 2, wherein said diimide constituent is a dimaleimide, maleimide, nadimide or allyl-nadimide.

10. Process according to claim 3, wherein said diimide constituent is a dimaleimide, maleimide, nadimide or allyl-nadimide.

11. Process according to claim 2, wherein the diamine constituent is based on an aliphatic diamine, advantageously supplemented by an aromatic diamine or a silicone diamine.

12. Process according to claim 3, wherein the diamine constituent is based on an aliphatic diamine, advantageously supplemented by an aromatic diamine or a silicone diamine.

13. Process according to claim 4, wherein the diamine constituent is based on an aliphatic diamine, advantageously supplemented by an aromatic diamine or a silicone diamine.

14. Process according to claim 5, wherein the diamine constituent is based on an aliphatic diamine, advantageously supplemented by an aromatic diamine or a silicone diamine.

15. Process according to claim 6, wherein the diamine constituent is based on an aliphatic diamine, advantageously supplemented by an aromatic diamine or a silicone diamine.

16. An encapsulated electronic component according to the process of claim 1.

Description

[0015] FIGS. 1 to 3 appended illustrate the implementation of a process of encapsulation according to the invention in the context of producing power modules having electronic components, such as those which are combined with transistors, for example of the MOSFET type, to form a rectifier bridge or inverter, as can be found in motor vehicle alternator-starters.

[0016] FIG. 1 shows a module enclosed in a housing as it comes out of the encapsulation plant and ready to be assembled in its connections with other elements of the same alternator-starter unit, whereas FIG. 2 more especially serves to illustrate the process of encapsulation itself, such as implemented for encapsulating the visible electronic components in the open housing of FIG. 3, together with the conducting circuits which are associated with these.

[0017] The components pre-assembled on plate 1 supporting printed connection circuits between components are disposed in a receiver housing 2 open at the top. The support plate rests on base 3. The connecting wires 6 have been welded to provide a connection between the components combined with transistors 7 and the printed circuits, as well as to set of connections 4 supported by the side wall of the housing on which other equipment will be connected. The figures also show electric power terminals 8, as well as wings 9 receiving bolts typically attaching the housing to a heat sink of the power electronics of the alternator-starter.

[0018] The mixture-pre-prepared to a liquid state, which is viscous to a greater or lesser extent by dissolving the diimide in diamine-is then poured into the housing in sufficient quantity so that all components there are immersed. Possibly a cover plate 5, which seals and protects the assembly, without however hampering set of connections 4, is then fixed on the housing completely filled with said composition. The curing of the material is then carried out by heat-polymerisation and cross-linking of the constituents of the starting mixture under the conditions which will be detailed in the following examples.

EXAMPLE 1

[0019] 3 grams of 2-methyl 1.5-diamino pentane and 7 grams of 1.4-di(maleimido) benzene, preferably at a temperature lower than 25° C., is gently mixed until a homogeneous mixture is obtained.

[0020] The paste, deposited on a substrate, is placed in an oven at 175° C. for at least 15 minutes.

[0021] The material finally obtained has a freezing fraction of approximately 90%, a mass moisture ingress under normal conditions of temperature and pressure of 5%, a degradation temperature at 5% mass loss of almost 300° C., a storage modulus of 2.7 GPa at 20° C., and a mechanical relaxation temperature of approximately 130° C.

[0022] A water drop deposited on the cured surface forms an angle of approximately 98 degrees, which proves its hydrophobic character.

EXAMPLE 2

[0023] One starts by preparing the solvent by hot-mixing 1.84 grams of 4-aminophenyl sulfonic acid with 2.16 grams of 2-methyl-1.5-diaminopentane until a limpid yellowish solution is obtained. The solution is then allowed to cool.

[0024] 3.5 grams of the above mixture and 6 grams of 1.4-di(maleimido) benzene are gently mixed, preferably at a temperature lower than 20° C., until a homogeneous paste is obtained.

[0025] This paste is not used for pouring into a housing as illustrated by the figures, but is applied as a solid gel to a set of components on their support plate, it being essential that they are completely covered.

[0026] The paste, deposited on a substrate, is placed in an oven at 175° C. for at least 15 minutes.

[0027] The material finally obtained has a freezing fraction of approximately 75%, a mass moisture ingress under normal conditions of temperature and pressure of 5%, a degradation temperature at 5% mass loss of 310° C., a storage modulus of 2.3 GPa at 20° C. and a mechanical relaxation temperature of approximately 180° C.

[0028] A water drop deposited on the cured surface forms an angle of approximately 105 degrees, which proves its hydrophobic character.

[0029] The introduction of an aromatic diamine enables the thermal degradation temperature to be increased. The mechanical relaxation temperature is also increased, which allows a stable Young's modulus to be reached over a wider range of temperatures.

EXAMPLE 3

[0030] 8.30 grams of a,w-aminopropyl poly-dimethylsiloxane and 3.75 grams of 1.4-di (maleimido) benzene are vigorously mixed, working under high vacuum, until a homogeneous mixture is obtained.

[0031] The mixture can be used for pouring into a housing as illustrated by the figures, is deposited on a substrate as in example 1, then placed in an oven at 125° C. for at least 15 minutes.

[0032] The material obtained contains a freezing fraction of approximately 60%, zero moisture ingress under normal conditions of temperature and pressure, a degradation temperature at 5% mass loss of 340° C., a storage modulus of 0.025 GPa at 20° C. and the mechanical relaxation temperatures detected of approximately −105° C. and 50° C.

[0033] A water drop deposited on the surface forms an angle of approximately 100 degrees, which proves its hydrophobic character.

[0034] The use of a diamine containing silicone in this example enables the thermal degradation temperature to be increased and the moisture ingress to be decreased (more hydrophobic material). The material obtained also has a storage modulus 100 times lower, which decreases the stresses on the electronic components. In addition, the mechanical relaxation temperature is also decreased.

[0035] From the above examples it is evident that the polymeric compositions to be used for encapsulating electronic components according to the invention will be implemented, for each case of application, in several different ways, which will vary in particular according to the viscosity of the mixture of diimide dissolved in diamine. This viscosity can in fact be that of a liquid applied by pouring into a housing acting as a mould, or rather that of a gel applied as paste without needing a mould. The electronic components, including their wiring, are completely immersed in the fluid material, so that they are covered in the solid mass obtained after heat-curing of the starting composition, the constituents of which are thus polymerised with cross-linking.

[0036] From the same examples, it is also evident that in all cases the mechanical and physico-chemical characteristics of the material finally obtained after curing of the initial composition correspond to the specifications usually required depending on the conditions of operation and use of electronic power modules. The material is homogeneous, the free surface is smooth and hydrophobic, insensitive to environmental attacks encountered in motor vehicle applications.

[0037] It still appears from these examples that if a simple aliphatic diamine such as 2-methyl 1.5-diamino pentane can be perfectly used as suitable reactive solvent for diimide, it may be more advantageous to prefer over this a diamine constituent containing an aliphatic diamine supplemented by an aromatic diamine compound as in example 2 or by a diamine compound carrier in addition to a functional group other than the silicone diamine of example 3. In each case the diimide is dissolved in diamine at normal temperature and the curing temperature used ranging between 80° C. and 200° C. remains. A reaction time of about 15 to 30 minutes at this temperature appears sufficient, which generally confirms the feasibility of under one hour.

[0038] It will also be noted that although the description more particularly details the case where the diimide constituent is a dimaleimide, the invention also includes the generalisation to other structures such as maleimide, nadimide and allyl-nadimide.