WO2005048452A1

WO2005048452A1 - Electrical component with encapsulation, and method for the production thereof

Info

Publication number: WO2005048452A1
Application number: PCT/EP2004/011830
Authority: WO
Inventors: Bruno FÜRBACHER; Hans Krüger; Wolfgang Pahl; Alois Stelzl
Original assignee: Epcos Ag
Priority date: 2003-11-04
Filing date: 2004-10-19
Publication date: 2005-05-26
Also published as: DE10351428A1

Abstract

The aim of the invention is to encapsulate an electrical component. Said aim is achieved by gluing the component chip to a support plate and joining the same in an electrically conducting manner to metallic connecting areas which are provided on the surface of the support plate and are connected to metallic terminal contacts located on the bottom face of the support plate. A cap that is provided with a cavity is glued to the support plate above the chip in such a way that a hollow space remains on the inside. Gluing can be done in a secure, slip-free manner and without damaging the points of adhesion with the aid of a compensation port that can be closed at a later point in time.

Description

Besehreibung

Electrical component with encapsulation and method of manufacture

^'' Electrical components that are built on a chip usually require an encapsulation or a housing to protect the chips against environmental influences. Components that are built on piezoelectric substrates require separate encapsulations because of the piezoelectric properties of the substrate material, in which a mass loading of the chip surface is excluded. For miniaturized components on piezoelectric substrates, for example SAW filters, for mobile communication, encapsulations are used today, for example, in which the chip is applied to a substrate in a flip-chip construction and is covered from the rear. The surface of the chip with the component structures between the substrate and the chip is protected in a cavity provided there, while the cover rests on the rear side, which is insensitive to the mass load.

With SAW filters for lower frequencies, for example less than approximately 1.00 MHz, the problem arises that the chip length increases with the decreasing frequency and thus with the longer wavelength, which makes the handling of the chips more difficult due to the sensitive piezoelectric material. In addition, such chips require a certain minimum length that far exceeds the width. This results in exceptionally elongated components, additionally complicates the handling of such chips and makes them more sensitive to breakage or damage.

Known encapsulations for such large and sensitive components usually consist of a two-part housing, the component usually being attached to a leadframe. is arranged. Such encapsulations are relatively large and usually for SMD T ^'technic not very suitable.

The object of the present invention is therefore to provide a component with encapsulation which is simple to manufacture, miniaturized and surface-mountable and yet ensures reliable protection for the chip.

This object is achieved with a component according to claim 1. Advantageous refinements of the invention and a method for producing the component can be found in further claims.

According to the invention, it is proposed to glue the component onto a carrier plate, to electrically connect it and then to cover it with a cap which is seated on the carrier plate. The upper side of the carrier plate carries metallic connection surfaces which are electrically connected to connection contacts on the underside of the carrier plate, for example in the form of so-called Castellations. The cap is glued to the carrier plate, a closed cavity being created below the cap, in which the chip is arranged and protected.

The carrier plate comprises a mechanically stable dielectric layer and is, for example, of a single or multiple ^'layered plastic material, preferably glass fiber reinforced. This has metallizations, at least on the top and bottom, from which the connection surfaces and connection contacts and, if appropriate, further circuit elements or electrical conductors are formed. A multilayer carrier plate has additional metallization levels between a plurality of dielectric layers, in which electrical connections for additional interconnection are arranged. In addition, passive components for electrical Adaptation may be formed, for example resistors, inductors or capacitors.

However, it is also possible to form the single-layer or multilayer carrier plate from ceramic. The thermal expansion behavior of the carrier plate is advantageously adapted to the material of the chip.

The chip is preferably formed from a crystalline piezoelectric material and carries on the top

Device structures. Such component structures are, in particular, interdigital transducers that are suitable for generating near-surface acoustic waves. As further component structures, reflectors can be arranged on the surface of the chip, as can electrical connection pads and conductor tracks connecting the structures. The chip is e.g. with the help of .Bondwires with the connection surfaces of the carrier plate conductively connected.

The electrical connection of the connection surfaces on the upper side of the carrier plate to the connection contacts on the underside of the carrier plate is preferably carried out via internally metallized through holes through the entire thickness of the carrier plate _^ These are preferably arranged so that their openings on the top of the carrier plate from the edge of the cap covered, or are arranged entirely or partially outside the cap, so that no hole opening into the cavity under the cap and this remains tightly closed '.

Alternatively, the through holes can be sealed later. In the case of multi-layer carrier plates with internal wiring levels, the holes in the individual layers can also be offset horizontally from one another in such a way that they are electrically connected so that there is also no leakage under the cap. In the production of components according to the invention, use is preferably made. For this purpose, a large-area carrier plate is first provided, which provides electrical connection areas and bores for a large number of chips and accordingly has a large number of component regions arranged next to one another. At the boundary between two adjacent component areas, dividing lines are intended, along which the individual components are later separated. The separation can take place, for example, using saws. The internally metallized bores are preferably arranged along the dividing lines and are therefore divided in the middle when they are separated. In this way, it is possible to assign an internally metallized bore to two component areas at the same time, so that a separate electrically conductive connection between the connection surface and the connection contact remains for each of the two component areas after the separation.

In an advantageous embodiment of the invention, the cap has a closable compensation opening. This opening serves to equalize the pressure between the cavity enclosed under the cap and the outside world during the gluing process. This pressure equalization prevents the cap from being overpressured when the adhesive is thermally hardened, for example in an oven. In the case of known closed caps, this is caused by thermal expansion, by evaporation of solvents or other volatile constituents of the adhesive or by the release of adsorbed and absorbed gases or low-molecular substances from the adhesive, the carrier plate or the cap. Up to now, such overpressure had to be compensated for by an increased outside pressure in the furnace. However, the problem arises here that the external overpressure must be selected to be exactly matched to the internal overpressure, so that the adhesive layer is not pressed inwards or outwards and thus does not result in leaks or inadequate fastening or slipping. see the cap on which comes as an air cushion overpressure. However, due to fluctuating material composition and changing partial pressures, exact adjustment is practically not possible. Alternatively, an isothermal process control (setting and curing of the adhesive at the curing temperature of the adhesive) had to be selected. This too could not solve the problem satisfactorily because of the other causes of overpressure.

According to the invention, the closable compensating opening also prevents the pressurized gases under the cap from making a path through the adhesive layer under the cap edge, either displacing the adhesive or even an open channel in the adhesive layer leading from the cavity under the cap would remain. Through the compensation opening in the cap, it is therefore possible to place the cap securely on the carrier plate, a clean adhesive connection being obtained. Outgassing caused by the curing of the adhesive and the thermal conditions used can also be discharged through the opening.

After the adhesive point between the cap and the carrier plate has hardened, the compensation opening is closed again, for example by dropping a reaction resin on it. A UV-curing or UV-initiated curing reaction resin is preferably used for this. The compensating opening is designed in such a way that the drop of the reaction resin used for sealing does not drip through the compensating opening into the interior under the cap. For this purpose, the compensation opening is preferably designed with a cross-section tapering downwards, that is to say in a funnel shape.

In an advantageous embodiment of the invention, the compensating opening which can be closed or which is closed again with the aid of reaction resin is located in the vicinity of an external connection contact and thus identifies pin 1, for example. To enable this marker to be recognized and in order to additionally obtain a process check as to whether the equalization opening is completely closed, the reaction resin composition is preferably mixed with a fluorescent dye. By excitation and measurement of the fluorescence, the clean closure of the compensation opening can easily be checked.

In a further advantageous embodiment of the invention, the adhesive for adhering the chip to the carrier plate is acoustically adapted. This means that the acoustic impedance of the adhesive material is matched to the chip, that is to say to the impedance of the piezoelectric material. This can be achieved by choosing either the modulus of elasticity and / or the density of the adhesive mass to be sufficiently high. An acoustically adapted adhesive preferably has a density between 2000 and 5000 kg / m ³ . Such a density is achieved, for example, with an adhesive which is filled with a high-density filler of more than 4000 kg / m ³ .

A suitable adhesive comprises, for example, a polymer matrix which is filled with ceramic particles. Ceramic particles of sufficient density consist, for example, of one or more of the following compounds: silicon carbide, titanium oxide, aluminum oxide, zinc sulfide, zirconium oxide, barium sulfate and tungsten oxide. These fillers are much cheaper than commonly used silver. On the other hand, the proposed fillers are dielectric and make it possible to apply an adhesive layer directly over current-carrying conductor tracks without there being a short circuit.

^• An associated polymer matrix is selected as desired and includes, for example, an epoxy molding material, a siloxane rubber, an acrylate, a polyurethane or a polyimide. With such an acoustically adapted adhesive, a good acoustic transition from the chip into the adhesive composition is made possible. This has the result that the reflection of bulk acoustic waves, which occur or can be excited undesirably in the component chip, is reduced on the underside of the chip. A reduction in the reflection on the underside of the chip “accordingly also means that less reflected waves find their way back into the acoustic path and thus avoid interference signals and an improvement in the transmission properties is achieved. This is particularly advantageous for components or SAW filters which are used for multimedia applications and in which undesired interference signals have particularly disadvantageous effects.

A further reduction in reflection of unwanted bulk waves on the underside of the chip is achieved if the underside of the chip has a roughening. It is also possible to structure the underside of the chip in three dimensions or to provide incisions. These incisions can be closed with an optionally filled reaction resin compound such as the above-mentioned adhesive or another plastic.

The method for producing a component is described in more detail below on the basis of exemplary embodiments and the associated figures. The figures serve only for a better understanding of the invention and are therefore only schematic and not drawn to scale.

Show it

Figure la is a large-area carrier plate with several component areas

Figure 1b shows a detail from Figure la with a single component area 2 shows a component area with a bonded and bonded chip

3 shows a component according to the invention with a cap in cross section

4 shows an inventive ^'sealed with cap device in a schematic plan view.

Figure la shows a large-area carrier plate TP, for example a single-layer plastic plate made of an FR4 or BT material. A large number of similar component regions arranged next to one another are provided in the carrier plate TP. Through bores DB are located on the dividing lines TL between the individual component areas and are metallized on the inside.

FIG. 1b shows a section of a component area BB of the carrier plate in a schematic elevation drawing. Each of these component regions BB has a plurality of internally metallized bores DB at least on a border line with an adjacent second component region. Each of the bores DB is connected to a connection area AF on the surface of the carrier plate per component area BB. The component areas BB can have the corresponding bores and any number of connecting surfaces AF connected to them on more than one side edge. Connection contacts AK are formed on the underside of the carrier plate TP, with at least one connection contact AK being assigned to each connection surface. Each connection surface AF is electrically conductively connected to a connection contact AK via the internally metallized holes DB.

Arranged within the component area delimited by the dividing lines TL is the chip area CB, which is provided for receiving the chip carrying the component function. The chip area CB preferably consists of a end faces, but usually not free of other metallizations surface area. For example, metallic connecting lines can be provided in the chip area. In one embodiment of the invention, the openings of the holes DB can be closed with a thin plastic layer before the chip is glued on, for example by laminating a plastic film onto the top of the carrier plate TP. In a structuring step, the plastic film (not shown in the figure) is structured in order to expose at least the connection areas AF. In a further embodiment of the invention, the plastic film is structured such that only the openings are covered or closed by the plastic film. This prevents the cap adhesive from running into the holes.

Figure 2: In the next step, a chip CH is glued to the chip area CB in each component area. This can be done with the aid of a reaction resin designed as a CK chip adhesive. The chip adhesive CK is preferably acoustically adapted and can have a low electrical conductivity, which can be generated, for example, by a suitably chosen filler. This enables static charge to be reliably discharged from the chip, which can occur in particular with pyroelectric chips. The chip adhesive CK is preferably thermally curing. The chip adhesive CK can also be a UV-initiated thermally curing adhesive which, after UV initiation, quickly achieves pre-curing, so that the chip placed in the chip area CB can be fixed quickly and securely after an adjustment, if necessary. The complete hardening can take place in a later thermal step, without the fear that the chip CH will slip. The chip adhesive CK can be applied to the carrier plate TP, to the chip CH or to both surfaces to be connected. The order of the _. Chip adhesive is preferably done by dispensing or

Stamp. If the chip adhesive CK is applied to the carrier plate TP, this can also be done, for example, by means of screen printing proceed for all component areas of the carrier plate TP simultaneously.

Figure 2 ^shows' in a fragmentary elevational drawing shown a glued chip CH. The component structures of the chip CH point upwards, where the connection pads BP of the chip CH are also arranged. The connection pads of the chip are then connected to the connection areas AF on the surface of the carrier plate via bonding wires BD.

In the next step, the cap KP is put on. The cap consists of a preferably injection-molded part made of thermoplastic or thermoset plastic, which may be filled with a particulate filler or with a fibrous material, e.g. is reinforced with glass fibers. A well-suited material that can also be processed with filler is e.g. PPS. The inside of the cap has a recess which serves to receive the chip, including its bonding wires BD used for contacting. can. The material thickness of the cap KP is selected so that it provides sufficient security against deformation over the entire length and width of the chip in the temperature range provided for the component and thus ensures reliable protection of the chip or its sensitive component structures against external influences.

An adhesive, which can be identical to the chip adhesive CK, is also used to stick on the cap KP. However, while the acoustic adaptation to the impedance of the chip CH is advantageous for the chip adhesive CK, this is not necessary for the cap adhesive KK. A reaction resin can also be used for this purpose, which is applied to one or both of the surfaces to be glued, that is to say to the lower edge of the cap KP or its projection onto the surface of the carrier plate TP, and is preferably thermally hardened. Here, too, the adhesive is optionally activated with UV radiation, then the cap KP is placed on it, adjusted if necessary and then temporarily fixed if necessary for a short waiting time. The thermal curing of the adhesive point KK of the cap KP can be carried out thermally in a later step, preferably together with the curing of the chip adhesive.

FIG. 3 shows a further detail according to the invention, which improves the gluing to the cap KP. In the top of the cap KP there is an opening which extends through the entire cap - the compensating opening AO - and which advantageously has a cross section which tapers inwards. During the placement of the parts to be glued and the complete hardening of the two gluing points CK and KK under the chip or cap edge, in which outgassing can possibly occur from the glue, pressure equalization can take place through the equalization opening AO, so that it does not lead to pressing away Adhesive under the edge of the cap or even the cap KP may slip. After complete curing, the opening AO is closed again, preferably by introducing a drop of a preferably UV-curing reactive resin composition into the opening. FIG. 3 shows a schematic cross section through the component after the cap has been stuck on and before the compensation opening AO is closed.

After the cap KP has been glued on, in particular after the adhesive KK used for this has hardened and the compensation opening AO has been closed, the components are separated. For this purpose, a cut or saw is made along the dividing lines TL through the carrier plate TP, so that for each component DB metallized internally, a so-called Castellation CA is created for each component on both sides of the dividing line TL, which in the finished component provides the electrical connection between the connection area AF on the top and connection contact AK guaranteed on the underside of the carrier plate. Figure 4 shows the finished isolated component in a perspective view. Components according to the invention are in particular large components with chip lengths of, for example, 6 to 10 mm. The Castellations CA exposed through the cut along the TL dividing lines are clearly visible. The circumference of the cap KP is chosen to be somewhat smaller than the component area remaining after the cut, so that the cap KP is not damaged by the cutting tool during the separation of the components. The separation can take place, for example, by sawing, the substrate preferably being cooled to avoid unnecessary heating, for example with water.

The finished component is characterized by its tight housing, can be processed using SMD technology and, for this purpose, has SMD-compatible external contacts AK. The chip CH carrying the component structures is securely glued to the carrier pallet TP and is therefore protected against breakage. When using a suitable chip adhesive CK with a sufficiently high density, a good acoustic adaptation to the chip and thus the low-reflection design of the underside of the chip can be achieved. During operation of the component, this leads to reduced rear-side reflections and thus to improved suppression of interference signals. Preferred use of components according to the invention can therefore be found in all multimedia applications which require low-noise and distortion-free signal transmission.

Although the invention could only be illustrated using a few examples, it is not limited to these. Variations arise in particular with regard to the component type, which is not limited to filters or chips made of piezoelectric material. There are further variations in the choice of materials and the shape of the KP cap and TP support plate. For example, multilayer carrier plates were not shown, which then also have a correspondingly varied form of contact between the contact surfaces and _A nschlußkontakten allow and do not require Castella Publications.

Claims

claims

1. Electrical component - with a carrier plate (TP) which has metallic connection surfaces (AF) on its upper side and connection contacts (AK) on its underside, which are connected in an electrically conductive manner to the connection surfaces - with a chip comprising piezoelectric material ( CH), in or on which electrically conductive component structures are arranged, the chip being glued to the top of the carrier plate, the component structures of the chip having the metallic connection surfaces on the top of the carrier plate

15 are connected in an electrically conductive manner - with a cap (KP) which sits directly on the carrier plate, forming a closed cavity containing the chip.

20 2. Component according to claim 1, in which the carrier plate (TP) and cap (KP) are each formed from a plastic material.

3. Component according to claim 1 or 2,

25. - in which the chip (CH) is a piezoelectric crystal, - in which the component structures are arranged on the top of the chip, designed to generate surface acoustic waves and - in which the component structures are bonded (BD)

30 the pads (AF) are connected.

4. Component according to one of claims 1 to 3, are provided in the rectilinear through the carrier plate (TP), on its inner wall metallized holes (DB) 35, via which the connection surfaces (AF) with the connection contacts (AK) are electrically connected , with the holes outside of the cavity enclosed under the cap (KP) are arranged.

5. Component according to 'Claim 4, - in which the base area of the carrier plate (TP) projects beyond the outer wall of the cap (KP) seated on it,

- in which the holes (DB) are partially covered by the cap,

- In which the outer edge of the support plate cuts the holes and they are therefore open on the outer edge.

6. Component according to one of claims 1 to 5, in which in the top of the cap (KP) a closable or subsequently sealed with a hardened resin opening (AO) is provided.

7. The component according to any one of claims 1 to 6, wherein the chip (CH) on its underside facing the upper side of the carrier plate (TP) has a roughening, a three-dimensional structuring or cuts extending up to part of its thickness.

8. Component according to one of claims 1 to 7, in which the chip (CH) with an acoustically adapted adhesive (CK) is glued, which has a density between 2000 and 5000 kg / m ³ .

9. The component according to claim 8, wherein the chip (CH) is glued with an adhesive (CK) comprising a reaction resin which is filled with a filler with a density of more than 4000 kg / m ³ .

10. Component according to claim 8 or 9, in which the adhesive (CK) comprises a polymer matrix filled with particles, in which the particles are selected from silicon carbide, titanium oxide, aluminum oxide, zinc sulfide, Zr0 ₂ , BaS0 ₄ and W0 ₃ and wherein the polymeric matrix is selected from Epoxidformstoff, siloxane _rubber. Acrylate, polyurethane or polyimide.

11.Component according to one of claims 6 to 10, in which the opening (AO) is arranged in the region of a corner of the cap (KP) over a terminal connection contact (AK) and in which the material with which the opening is closed, opposite the cap can be distinguished optically or in UV.

12. Method for encapsulating an electrical component, with the 'steps

- Prepare a large-area carrier plate (TP) with electrically conductive connection surfaces (AF) on the top and contact surfaces (KF) on the underside and with holes (DB) metallized on the inner wall so that a large number of component areas (BB) are obtained

- Stick on. one component ή having chips (CH) per component area on the top of the carrier plate

- Establishing bond wire connections (BD) between the component structures and the connection surfaces

- Placing and gluing one cap (KP) per component area on the carrier plate above the chip so that the chip is arranged in a closed cavity.

13. The method according to claim 12, in which the carrier plate (TP) after the caps are attached and glued (KP) along dividing lines (TL) between the individual component regions (BB) and separated into individual components.

14. Experience according to claim 13, in which the bores (DB) are produced along the later dividing lines (TL), in which each bore is assigned to two component regions (BB) and connection surfaces (AF) within these component regions. rich with the corresponding connection contacts (AK) electrically conductively connects at which the holes are divided as in the separation, that the electrically conductive connection (CA) circuit surfaces and between the on ^'the associated connecting contacts within each device region is maintained.

15. The method according to, one of claims 12 to 14, in which the cap (KP) is glued to the carrier plate (TP) with an adhesive (KK), the curing of which comprises at least one thermal step.

16. experience according to one of claims 12 to 15, in which an opening (AO) of comparatively small diameter is provided in the cap (KP) for pressure equalization during the bonding, in which the opening after curing of the adhesive points of the cap (KP ) and Chip (CH.) is sealed with a drop of a reaction resin.

17. The method according to claim 16, in which a light or UV-curing reaction resin is used to close the opening (AO), in which the reaction resin is hardened by irradiating the entire surface of the carrier plate or by local irradiation with a laser or a light guide.