CS268940B1 - Method of encapsulation of electron and electrotechnical components - Google Patents

Abstract

A method of encapsulating electronic, electrotechnical and semiconductor components consisting in that, on the components placed in the solution, a first encapsulating layer is first applied, consisting of a telechelic polya1loxane containing vinyl groups and a diacetyl-acetyl/hydrogensiloxane copolymer, and after vulcanization in the presence of a catalyst on rhodium or platinum, a second protective and mechanically fixed layer is applied, consisting of an epoxy resin, while some components may first be coated with a special bonding layer. This method of encapsulation is suitable for power semiconductor components and for components containing solder joints, thin wires or other easily vulnerable parts.

Description

The invention relates to a method of encapsulating electronic and electrotechnical components, for example semiconductor components, which is particularly suitable for components containing soldered joints, thin wires and other easily vulnerable systems.

Plastics are very often used to protect electrical and electronic components, such as hybrid integrated circuits, power semiconductor circuits, transistors, etc., from the effects of moisture and corrosive substances present in the air. After the usual protection of the electron and hole junction of the semiconductor with special high-purity coatings (junction coating) such as alkali-free low-melting glasses, or silicone rubbers and varnishes, polyimide varnishes and the like, encapsulation in plastic follows, usually involving epoxy potting or molding compounds or other thermoplastics (diethyl phthalates and the like).

These materials, characterized by high hardness and high elasticity, have, in addition to undeniable advantages such as good adhesion to various surfaces, sufficient processing properties, low wettability, as well as certain disadvantages. These include, in particular, high internal stresses arising during the shrinkage of the plastic after hardening, which, together with the different expansion of the materials used (plastics, metals, ceramics, etc.), leads to the formation of cracks and fissures in the plastic, which results in a reduction in its protective function or disruption of the connections of integrated circuits, transistor modules, etc., and thus an increased failure rate of components and modules. On the other hand, some flexible elastomers, such as silicone rubbers, do not exhibit sufficient mechanical properties to protect components against mechanical damage. These disadvantages are eliminated by the method of encapsulating components according to the invention.

The essence of the invention is a method of multilayer encapsulation of electronic and electrotechnical components, and in particular semiconductor components, consisting in applying a first encapsulation layer to the components, consisting of a telechemical polysiloxane containing vinyl groups » d.1methyl-methyl/hydrogen/siloxane copolymer and after its vulcanization in the presence of a rhodium- or platinum-based catalyst, a second layer, consisting of an epoxy resin, is applied, whereby the components can first be passivated with a special passivation layer.

A great advantage of the encapsulation according to the invention is the low internal stress in the places of contact with the individual components. After vulcanization, the silicone material is sufficiently flexible to compensate for the expansion even with a large difference in the temperatures of the individual places - the circuit is not mechanically stressed and cracks in the material do not occur in the inner protective layer as a result of the different dilated materials used, thus the possibility of gaps usually forming between the plastic and the surface of the semiconductor system is suppressed. Therefore, the protective function of this layer remains preserved even in demanding climatic and operating conditions. On the other hand, the outer layer of hardened epoxy resin serves primarily for mechanical fixation and protection as well as for the overall strengthening of the module containing the encapsulated components.

Another advantage of this encapsulation method is that hydrosylation vulcanizable silicone compounds can be prepared in high purity and with excellent electrical insulation properties, which increases the operational reliability of the encapsulated components and at the same time reduces the requirements for the purity of the epoxy potting compounds forming the underlying protective layer. The properties of the epoxies can then be optimized in terms of mechanical properties, application technology and price.

The advantage of this method of encapsulation is also the easy repackaging of components in the event of a banal defect in the electrical circuit (broken wire, etc.) or system. This fact is particularly important for the encapsulation of power components, where a significant part of the price of the components is the semiconductor system itself. The housing can be mechanically disassembled and the gel removed with organic solvents. When encapsulating in epoxy molding compounds, repackaging of the component is very difficult and often impossible without a significant risk of damaging the encapsulated system or electrical circuit.

The following examples illustrate the encapsulation of the invention without limiting or limiting it.

Example 1

The power potential-free thyristor module, which consists of two antiparallel connected thyristors < passivated PNPU junctions with a specially pure silicone coating, placed on ceramic substrates made of corundum ceramics and pressed by a suitable structure to a copper base, on which there is an outer cover made of epoxy molding compound around the circumference, was cast from a mixture of telechelic poly(dimethylsiloxane), dimethyl-methyl/hydrogen/di loxane copolymers and a platinum-based hydrolyzed catalyst. After the silicone potyacr has been vulcanized for 2 h/100 °C, the upper protective layer is formed from a completely unfilled palm-type epoxy resin with a latent catalyst. The whole is closed with a mold of molding compound and cured for 5 h/150 °C.

Example 2

Power potential-free thyristor transistor module, consisting of two PNP transistors, passivated at the junction with a special polyimide varnish, powered on corundum ceramics provided on the lower side with a copper foil clad on the ceramics by the technique of direct bonding of copper to ceramics /at a temperature of 1,065 °C to 1,083 °C in an inert atmosphere with a small addition of oxygen - typically hundredths of a percent/, manufactured in such a way that the clad ceramics forming the front surface of the module are, after cementing the ceramic chips into the base of an epoxy molding die, poured with a mixture of telechelic polysiloxane terminated with a group of I«kup1nam, diethyl-methyl/hydrogen/siloxane copolymer and a rhodium-based hydrosilation catalyst. After vulcanization of the silicone polymer for 1 h/150 °C, the upper protective layer - after the epoxy molding outer shell has been cemented - is formed by pouring a palm-type epoxy resin filled with ground quartz and an aromatic phthalate-based hardener. The whole is closed with a polyethylene terephthalate cap and cured for 2 h/80 °C ♦ 4 h/150 °C.

Claims (1)

A method of encapsulating electronic and electrotechnical components, characterized in that a first encapsulating layer formed by a telechelic polysiloxane containing vinyl groups and a dimethyl-methyl/hydrogen/siloxane copolymer is applied to the components and, after its vulcanization in the presence of a rhodium- or platinum-based catalyst, a second layer formed by an epoxy resin is applied.