DE202006006610U1 - Housing for e.g. micro-bolometer, has substrate with electrical circuit, another substrate arranged opposite to former substrate by free volume, and frame on both sides of boundary area and confining volume - Google Patents

Abstract

The housing has a substrate with an electrical circuit, and another substrate arranged opposite to the former substrate by a free volume. A frame (104a) on both sides of a boundary area confines the volume and is made up of a metal, where the area is arranged between the substrates and comprises an alloy of the metal and another metal. Melting temperature is the latter metal is smaller than that of the former metal and the alloy.

Description

The The present invention relates to packages for electrical circuits and especially with such housings, which is an electrical circuit in a sealed volume encapsulate.

applications in which electrical, optical, micromechanical or other components within a housing have to be arranged to ensure their functioning are manifold. For example become infrared sensors for infrared cameras, Thermal imaging cameras or imager for night vision devices within from closed enclosures to avoid damage or distort the measurements environmental influences appropriate. In the micromechanical area, this also applies to gyroscopes and electrically adjustable micromirrors and other mechanical Components, such as micromechanical sensors. For cameras for visible Light or other sensors need as well as individual sensors, sensor lines or whole two-dimensional ones Arrays within a housing to be ordered.

at Some sensors, such as bolometers, are included the requirements for the housing extremely high if this must enclose the sensor, but without the functionality of the sensor thereby to impair that through the case the size to be measured by the sensor is falsified. For a bolometer, essentially for measuring temperatures over the Detection of radiated infrared radiation, housing are particularly complicated to manufacture, as will be explained briefly below.

A bolometer, as for example in 6 The infrared radiation is essentially measured by absorbing the radiation in a material mounted within the sensor, the temperature and resistance of which is thereby changed. Such a membrane 2 , which consists of a material with finite electrical resistance, changes this resistance depending on the temperature increase and the temperature coefficient of resistance. However, this results in the problem that the temperature change of the resistor due to the low incident energy of the heat radiation in the infrared range is very low (a few milli-Kelvin). Therefore, it is at the in 6 particularly important, the membrane 2 thermally isolated from a carrier substrate 4 in order not to influence the extremely sensitive measurement by the fact that the membrane temperature by thermal conduction through the terminal contacts of the membrane 2 artificially changed. The success of the measurement depends so much on the fact that the resistor is well mounted thermally insulated. This is generally achieved by using the membrane 2 over connections 6a and 6b connected to the substrate, which have thin, long arms, as in 6 you can see. These arms have a relatively high thermal resistance, since their heat-transporting cross-section is very small.

As on such an integrated component, the large-area membrane 2 at a short distance to the substrate 4 is arranged, it is also required, the heat conduction through the gap between the membrane 2 and substrate 4 to prevent. Since the most efficient heat transport takes place via convection, it is necessary to have the environment of the bolometer or the membrane 2 to evacuate. This is generally realized in the prior art by mounting the microbolometer chip as such in a housing which can be evacuated. The 7 and 8th show an example of such a prior art housing, in particular the exploded view in 7 it can be seen how complicated the production of such a housing. Such, typically made of metal metal housing are therefore very expensive, so that their use for the mass market is not suitable. In addition, due to the complete encapsulation of the entire chip through the housing, the housing volume is significantly larger than that of the actual detector chip.

object intense efforts it was therefore younger Past, to develop procedures that the housing of a Already allow component on the wafer level.

For example, US Patent Application 5895233 describes how to make a package that is barely larger than the detector chip itself. In this case, microbolometer arrays are produced on a substrate or a first wafer. Around each array, a frame is made of metal, on which solder is deposited. A lid wafer is made, which is also provided with a variety of solderable metal frame. In this case, the arrangement of the frames on the second wafer is a mirror image of the frames on the first wafer. In a wafer bonding method, first the lid wafer is then mounted upside down on the substrate wafer, wherein each frame of the lid wafer comes to lie on the corresponding frame of the substrate wafer. Then both wafers are soldered together under protective gas or under vacuum. To isolate the chips, the resulting layer structure is subsequently sawn and decomposed into the individual detector chips. Based on this basic idea, there are a number Further developments, which are shown for example in US patent applications 6479320 B1 and 6521477 B1.

this Method is common that they are relatively compact detector chips to lead. However, due to the procedure, these methods have some serious disadvantages. First have to the substrate or wafer and lid are typically the same be great. You lose the flexibility, the lid and the substrate from various sources and production sites. Lid that made of special materials with precisely defined physical Properties must exist are usually not available in the large diameters that common for silicon wafers are. This is especially true for micro-bolometric Systems where the lid at the same time the entrance window for the radiation is and thus a high permeability must have in the infrared spectral range.

At the Solder itself there is the problem that the wafers must first be adjusted and after the adjustment, be put together in a vacuum chamber have to, where they are then pressed together and soldered. To be in this process not jeopardize the adjustment, is a complex transport and vacuum device needed.

One another big one Disadvantage is that in such a bonded and soldered structure only the two backs the original one Wafers are visible. Without additional elaborate measures are thus possibly attached to the wafer surface alignment marks, which are necessary to use a wafer saw to separate the wafer to saw not visible anymore. Even if the saw lines between the detector chips are known, is the sawing process itself extremely complicated, typically the lid wafer is different than the substrate wafer serrated must, for example, bond pads on the substrate wafer after sawing freely accessible are. Therefore, in general, the lid wafer is a smaller one area auszusägen as from the substrate wafer. Are different materials of the Lid and substrate wafers also significantly in their Composition or its strength, can a common sawing impossible be because it destroys one of the substrates. Another disadvantage relates to the cost of the method, especially when the lid wafer Made of special material and therefore expensive. Has the substrate wafer a bad yield (many defective dikker chips) will be the most expensive Lid wafers are not optimally used as both intact and on defective chips a lid is bonded.

One Another disadvantage relates to the method of soldering, for example a glass solder or a low melting eutectic (e.g. Au / Sn, 80% / 20%, 280 °) is used. By conventionally applied solder is the distance between substrate and lid wafer not easily reproducible adjustable because the solder in different Strengthen is deposited. To ensure at least a minimum distance Often, a cavity is etched over each chip in the lid wafer. The Depth of this cavity gives then a minimum distance to the surface of the substrate wafer before. However, this process is laborious and requires a number of additional Process steps above In addition, the deposition of the metal and Lotrahmens on the cover chip make it more difficult. Also, when using soft solder, the temperature the further processing of such packaged chips strong limited.

For connecting CMOS chips, a technique has recently been developed in which individual chips are deposited on a substrate wafer with a high-speed flip-chip bonder. Christoph Scheiring et al., IMAPS 2004, Long Beach, Nov. 14-18, 2004, describes an application "Advanced Chip-to-Wafer Technology: Enabling Technology for Volume Production of 3D System Integration on Wafer Level". Designed to electrically connect different CMOS chips, the substrate wafer can be fabricated with CMOS logic chips, the cap wafer is made from memory chips, and the cap wafer is sawn after applying a solder frame Lids are bonded to chips of the substrate wafer that are also "well" tested, and no soft solder is used, but the solid-liquid interdiffusion (SLID) technique is used to form a layer of low-melting metal such as tin (Sn) brought between upper and lower layers of higher melting metal, eg copper (Cu), and melted at low temperature, the Sn now diffuses up and down in d As Cu. This forms a higher melting compound, such as Cu ₃ Sn, this solidifies and connects the two Cu layers.

The construction of micro-electromechanical systems (MEMS) often uses the SLID technique to connect individual components of the system. SLID is based on that in a suitably chosen two metal system in which one metal has a lower melting point than the other metal, a stable alloy having a higher melting point than the lower melting metal can be formed. Such metals are brought into contact with each other and above the melting temperature of the lower melting metal, this melts and diffuses into the higher melting metal, so that forms an alloy at the boundary layer, which in turn has a higher melting temperature than the lower melting material with a suitable choice of partners. If the geometrical conditions are suitably chosen, the lower-melting metal melts completely and forms at the junction a higher-melting and thus solid alloy, in which the lower-melting metal is completely contained.

The US Patent Application 6793829 B2 describes that micromechanical Components with the layer sequence CR / AU / IN / AU / CR on each other this type can be connected. It is shown that a substrate with micromechanical components with a lid made of silicon, glass or ceramic, for example can be connected through SLID. The US patent application 2004/0266048 A1 describes a similar Method.

outgoing from this prior art, the object of the present invention, to create an efficient manufacturable housing.

These The object is achieved by a device according to claim 1.

Of the Present invention is based on the finding that a housing with an electrical circuit can be made more efficient, when on a substrate with a plurality of electrical circuits the circuits on functionality checked be and if the functional Circuits by means of a circuit on the surface of the Substrates enclosing Frame to be connected to a second substrate whose area is smaller is than that of the first substrate. The substrates are by means of a second frame adapted to the first frame on the surface of the second substrate so connected that the first and the second frame lie on one another. After that you can the functional ones packaged Circuits are technologically easily separated.

at an embodiment The present invention relates to electrical circuits on a wafer only then housed, if this by exam as functional were detected. In this case, the electric circuit is first a Frame on the surface the circuit carrying or integrating substrate is formed. Then, a lid is provided consisting of a second substrate, also a mirror image of the frame of the first substrate arranged frame. To create the case for the functional electrical circuits cover so applied that initially the frame the two substrates aligned and then with each other get connected. The separation of the fully packaged electrical circuits happens only after creating the housing on the wafer, which is below has the advantage that only one wafer material, namely that of the Wafers or substrates with the electrical circuits, by means a wafer saw sawn must become.

Furthermore the housing of the invention has the huge Advantage that the geometric extent of the cover is arbitrary, so that, for example, the lid can be smaller than the finished processed Component. So can For example, bond pads for contacting the component outside of the housing Area remain to a later Contacting the enclosed component using standard methods to enable.

at a preferred embodiment the present invention, the two frames by means of a SLID process connected in which as metallic phases copper (Cu) and tin (Sn) to be used over the melting temperature of the tin are heated so that through Diffusion of the tin in the copper forms an alloy whose melting point higher than that of tin is, so after a period of typically a solid metallic compound has been formed for a few minutes, the above In addition, electrical power can conduct well.

The SLID technology has the big one Advantage that the layer thicknesses of the materials used by means Standard coating process can be set extremely accurately, so that a distance between the first and the second substrate with high precision is adjustable when the substrates by the method described be connected to each other.

at a further embodiment In the present invention, the final bonding of the substrates performed in a vacuum, such that after connecting the first substrate to the second substrate a closed volume is formed between the two substrates is, in which the gas density is greatly reduced.

It It should be noted that completely material-free space and thus a perfect vacuum can not be produced is. Technical vacuums can however in different qualities getting produced. One differentiates in the technology different qualities the obtained vacuums are measured according to the amount of remaining matter (measured by the pressure in Pa = Pascal or mbar = millibar):

For the entire context of this document, therefore, the term vacuum designates an environment in which the remaining matter or molecular concentration is less than 10 ¹⁹ / cm ³ .

at a further embodiment According to the present invention, the frame is produced so that its first metal, which is on the substrate side facing is completely enclosing the electrical circuit while the second metal with lower melting point on the surface of the Frame applied in separate sections so that between the sections one is not the second Metal filled Volume is created. This has the great advantage of having a gas inside of the housing to be formed sucked through the resulting gap between the frame easier can be when connecting the frame in an evacuated Environment should take place.

at a further embodiment According to the present invention, the second substrate is first temporarily by means of connected by a suitable connection method with the first substrate. After all substrate covers on the positively tested electrical circuits of the first substrate are applied, so the wafer is completely processed was, the wafer with the provisionally attached substrate lids transported to a heatable process chamber for final processing. This has the big one Advantage that the relatively time consuming connecting, in which the Melting temperature over a certain, by the diffusion of the low-melting material certain time exceeded must be able to be separated from the operation of the alignment what significantly increased the process throughput.

at a preferred embodiment According to the present invention, the housing is used for a substrate or produced a wafer on the surface microbolometer were processed. As microbolometer, as already described, radiation in the infrared range have to be sensitive is an extremely thin lid chip or a lid chip with excellent optical properties necessary to ensure operation of the bolometer. About that In addition, the construction of resistive bolometers requires that the Volume in which the bolometer is located, to a certain extent Degree is evacuated. The method, two substrates by means of a Frame of metals that can form an alloy together connect, is particularly advantageous in two ways.

It should be noted here that infrared radiation or thermal radiation in physics refers to electromagnetic waves in the spectral range between visible light and the longer wavelength microwave radiation. This corresponds to a wavelength range of about 780 nm to 1 mm. For short-wave IR radiation One often speaks of "near-infrared" (NIR), at wavelengths of about 5 ... 20 microns of "mid-infrared" (MIR). Extremely long-wave IR radiation is called "far-infrared" (FIR). It borders on the area of terahertz radiation. Since the boundaries of the spectral ranges are fluent, the term infrared or infrared spectral range is to be understood in the context of the entire document synonymous with a wavelength range of 700 nm to 2 mm.

To the One can be different by the method of SLID Connect substrate materials together, so this particular also for the sensitive entrance window for infrared radiation applies. To the Others, the method is particularly suitable because of the Connection one completely metallic connection between the upper and the lower substrate which is per se a high gas impermeability has, so that it is possible according to the invention, already at the wafer level the sensor efficient and complete to encapsulate. It can within the encapsulated volume a nearly any gas composition, in particular a vacuum produced become.

at the proposed housing technology Thus, individual lid chips are bonded to a substrate wafer, using the SLID technique. To every chip on the substrate is a frame made of Cu / Sn applied, each lid is with a provided matching Cu frame. The lids can additionally with an adhesive layer be placed by means of which they placed on the substrate and provisionally "attached" in one can take another step now in a second plant all lids under vacuum (or under Inert gas) are soldered simultaneously in the SLID process. One eventually Applied adhesive layer evaporates there. Subsequently, the Chips are separated and further processed individually.

Thus, according to the invention create a vacuum-tight connection between substrate and lid, which avoids a number of disadvantages in the prior art. Such a miniature housing is for Infrared sensors as well as for Micromechanical components can be used particularly advantageously.

preferred embodiments will be described below with reference to the accompanying drawings explained in more detail. It demonstrate:

1 an example of substrates to be joined according to the invention;

2 , an example of the layered structure of a frame according to the invention;

3 an example of a fully processed device;

4a and 4b Illustration of the inventively achievable increase in process efficiency;

5 a flowchart for an example of a manufacturing process;

6 an example of a microbolometer;

7 an exploded view of a vacuum housing according to the prior art; and

8th an example of a vacuum housing according to the prior art.

The 1 shows an example of inventively prepared substrates for producing a housing.

1 shows a first substrate 100 or a wafer, wherein here only a section of a wafer is shown, which comprises a plurality of the in 1 includes sections shown.

In addition, a second substrate or a cover chip 102 shown.

In the sectional view of the wafer 100 and the lid chip 102 are beyond that on the wafer 100 Cross sections of an electrical circuit on the wafer 100 surrounding frame 104a and 104b shown. The complementary counterparts, frame according to the invention 106a and 106b the second substrate or the lid chip 102 is in 1 also shown.

According to the invention, the frame of at least one of the substrates consists of a layer sequence of two metals, which together can form an alloy whose melting point is higher than the melting point of the lower melting of the two metals. The frame 104a respectively. 104b therefore consists of a first layer 108a made of copper, on which a second layer 108b made of tin is applied. Likewise, the first wafer 100 facing layer of the frame 106a respectively. 106b of the lid chip 102 made of copper, so that the coating of the two chips according to the invention results in a layer sequence Cu / Sn / Cu.

According to the invention, the two chips can now be interconnected by SLID (Solid Liquid Interdiffusion), since Cu and Sn, a metastable phase Cu ₆ Sn ₅ with a melting temperature of 415 ° C and a stable phase of Cu ₃ Sn having a melting temperature of 678 ° C. can form. Since tin itself has a melting temperature of about 251 ° C, when the superimposed substrates, for example, at a temperature of about 300 ° C for a long time he heated, a metallic compound between the wafer 100 and the lid chip 102 produced. Depending on the duration of heating, the metastable or stable phase is formed. In order to avoid additional unwanted diffusion of wafer materials into the copper layer, or to allow the adhesion of a copper layer on the surface of the wafer in general, as in 1 can be seen between the copper layer 108 the frame and the wafers additional metallic layers are attached. An example of such layers is the one in 1 shown layer 112 , which is first attached as an adhesive layer of pure titanium on the wafer surfaces, whereupon a layer of TiN is disposed between the titanium layer and the copper layer as a diffusion barrier.

In the process according to the invention, therefore, individual cover chips 102 on the chips of the still undivided substrate wafer 100 bonded. As connection technique, the SLID method is preferably used. The starting substrate used is preferably a silicon wafer, on which an electrical circuit, such as a bolometer array, is created, and which is also referred to as a substrate wafer.

One another example of an electrical circuit of a processable wafer is for example one Arrangement of a plurality of micromirrors or other micromechanical Elements.

Before In the manufacturing process, the bolometer membranes by removing a typically exposed sacrificial layer will be exposed the wafer around each chip a ring of adhesive metal (for example Ti, 50 nm), a barrier (for example, TiN, TiW, 120 nm), a Layer of a refractory metal (for example Cu, Ag, Au, 5 μm) and low-melting metal (for example Sn, In 3 μm). This can be done by conventional sequential electrodeposition of the layers on one with photoresist (for example 8 μm) provided wafers happen when the paint in the area of metal rings was exposed and developed away.

The deposition by means of conventional methods, which may also include, for example, sputtering and other layer-wise deposition methods, has the great advantage that the layer thicknesses and thus the distance between the wafer 100 and the lid chip 102 can be set or reproduced extremely precisely.

For the further considerations, a layer sequence of Ti / TiN / Cu / Sn, as used in 1 can be seen, wherein the lid wafer is also provided with a layer sequence of Ti / TiN / Cu. The specific choice of the material is by no means compulsory for the successful application of the method, other material components by means of which SLID methods are possible are likewise suitable for implementing the inventive concept. Will, as based on 1 Shown as melting metal tin (Sn) can also be applied to a tin layer on the lid chip 102 be waived if the tin layer already on the wafer 100 is appropriate. Alternatively, however, it is of course also possible to coat both frames with tin. In addition, the tin layer can not simply be applied directly to the galvanically deposited copper ring. It is also possible, after the deposition of copper, to apply a further photovoltaic technique to the wafer, which restricts the surface for the further deposition of the tin, as is shown by way of example in FIG 2 you can see.

The 2 shows as an example that on the copper layer 108a of the frame a tin layer in blocks in blocks 120a and 120b is applied to the copper layer 108a do not completely cover. This prevents molten tin from leaking sideways when melting the tin, and may cause a short circuit to possible adjacent Cu bumps during soldering. Another significant advantage of such an arrangement is that passing through the tin blocks 120a and 120b formed channels on the surface of the copper ring 108a allow safe evacuation of a volume trapped by the ring when the lid chip 102 already on the wafer 100 is stored. During the actual soldering, the channels run through the molten tin, so that the entire system is ultimately tight. A struk turing, as in 2 can be seen or any other type of fine structuring can be generated in the soft tin, for example, by means of a stamp.

Order from the in 1 shown situation to arrive at a fully processed housing, as in 3 can be seen, a series of steps, which will be briefly presented below, is required. First, the lid chip 102 for which it is typically sawn from a wafer on which the frames have already been processed.

Then, the lid can be provisionally fixed to the substrate wafer, wherein in the simplest embodiment of the lid 102 only on the wafer 100 is filed.

In a preferred embodiment of the present invention, the bonding head, by means of which the cover chip 102 is kept at storage, heated and held with the metal frame down. Then an adhesive layer (for example, Bibenzyl or ethylene glycol, EC 2000) is applied. In this case, the bonding head is heated to, for example 60 ° C, so that the adhesive layer material with a melting point of about 55 ° C on the heated lid chip remains liquid. Of course, other adhesive materials with possibly higher melting temperatures are possible as long as the melting temperature of the adhesive material is below the melting temperature of the lower melting metal.

Of the movable bondhead is adjusted to the substrate wafer so that the Frame of the lid and the chip on the substrate wafer directly to each other demonstrate.

By lowering the bonding head of the cover chip 102 on the substrate 100 pressed. If adhesive layer material was previously attached, it will cool and solidify when the substrate 100 is significantly colder than the melting temperature of the adhesive layer material or the bonding head.

If no special adhesive layer material is used, there may be a temporary connection between the frame of the lid chip 102 and the frame of the wafer 100 For example, be prepared by friction welding, when the bonding head has a temperature of about 100 ° C and the cover chip 102 when settling relative to the wafer 100 is moved. This can additionally be supported by an ultrasound source.

According to the invention, this process of adjusting or connecting the lid chip 102 with the wafer 100 repeated until all desired chips on the substrate wafer are provided with a lid.

Then all lids are simultaneously on the wafer 100 fixed by soldering. This is the wafer 100 brought with the lids in an evacuated solder oven, and initially heated to a first temperature (for example, 50-100 ° C). Thereafter, the chamber of the furnace can be evacuated, wherein additionally a purifying flushing of the volume of the furnace with a suitable substance, such as formic acid, can be provided. After the cleaning, a new evacuation of the furnace can take place.

The actual bonding of the substrates over the frame is carried out by heating to a second temperature (in the example of the Cu-Sn system, for example, to 300 ° C). If this temperature is maintained for a few seconds, the molten tin diffuses into the copper. First, a metastable phase is formed, the Cu ₆ Sn ₅ phase. If the heating is maintained for longer than about 30 minutes, the stable Cu ₃ Sn phase is formed.

When connecting the cover chips 102 be pressed within the brazing furnace by means of a heatable elastic membrane on the substrate. Alternatively, the connection can also be made without pressure, with the additional advantage that the molten tin to minimize its surface energy, the lid chip 102 on the copper frame of the wafer 100 centered and virtually automatically adjusted, this adjustment is more accurate than that of a conventional bonding apparatus.

It should be noted that the metastable phase is already present after a few 10 seconds, so that in one variant of the method the processed wafer during the time of conversion of the Cu ₆ Sn ₅ phase in the Cu ₃ Sn phase in another batch Furnace can be annealed under vacuum together with other wafers, so as not to reduce the throughput of the entire process.

In an alternative embodiment, instead of the preferred SLID technique, the lid may also be used with conventional solders are soldered to the substrate (for example, Au / Sn solder).

After applying the lid chip 102 and vacuum soldering the lids are protected by the sensitive IR sensor arrays of the bolometers. After that, the wafer can 100 be sawn into the individual chips, with an example of such a chip in 3 or 7 is shown. After separation of the chips, the IR arrays can be further processed by chip-on-board technology or other assembly methods (for example, by attaching a flexible printed circuit board).

3 shows an example of a bolometer chip made according to the invention 200 , on its first substrate 100 sensitive sensor pixels 202 are arranged. There are bond pads 204a and 204b for electrical contacting of the pixels 202 arranged outside the housing. The lid of the case 204 is according to the invention via a frame 206 with the substrate 100 which was connected by SLID and thus has the characteristic material order Cu-Cu ₃ Sn-Cu, as it arises in the SLID bonding of Cu and Sn.

A great advantage of the inventive concept is based on 3 immediately apparent. The lid wafer does not have to be the same size as the substrate wafer due to the manufacturing process, so that configurations as in 3 become possible only in which bond pads are arranged outside the housed area, so that they are freely accessible after separation.

Compared to the prior art corresponding methods are also in the cover chips 102 No cavities necessary because the high-melting material (copper) is not softened during manufacture and thus corresponds to the distance between the substrate and the lid at least the sum of the thicknesses of the two copper layers.

In the case of the copper and tin system, a preferred brazing temperature is about 300 ° C. The resulting compound is extremely temperature-resistant, since the melting point of pure copper at 1085 ° C and the stable phase Cu ₃ Sn at 678 ° C. It is noteworthy that even the metastable phase Cu ₆ 5n ₅ already has a melting temperature of 415 ° C, so that a produced within a few seconds Cu-Cu ₃ Sn compound in a further annealing at 300 ° C is no longer separable, so that, for example, the housing produced can be processed further with normal soldering steps, even if the stable phase has not yet been reached.

Another advantage of the scattered placement of the substrate with lid chips 102 is that individually stapled covers evacuate much easier than the entire surface of the wafer 100 Covering lid wafer. In addition, tin is only locally deposited by galvanic or other steps on a copper ring, as in 2 is shown, the evacuation of the individual cavities is particularly easy.

Another great advantage of the method is that only the well-tested chips of the substrate wafer 100 must be provided with a lid, as indicated by the 4a and 4b is shown.

In 4b is initially a processed wafer 300 shown, which has at regular intervals processed chips or electrical circuits or micromechanical components.

In the selected wafer 302 only those electrical circuits are shown that have been found by a quality test to be functional. As can be appreciated, in view of the resulting costs, it is advantageous to provide only those electrical circuits with a cover chip or a second substrate, which are also functional, so that the total in 4a shown scenario, where starting from a wafer 304 only those areas are equipped with lids that have passed the bump test. After the preliminary bonding results in a wafer arrangement 306 , which is then processed by soldering, which can be done, for example, with additional exerting a force on the lid chips finished.

Particularly interesting and cost-saving is the individual placement when the lid chip itself contains a circuit and thus is relatively expensive. In addition, of course, only defect-free lid chips are selected for bonding, so that the overall yield of good chips is potentially significantly higher than wafer-to-wafer bonding, where a finished processed wafer 100 is connected to a finished processed lid wafer in a single step, with a resulting component already is useless if only one of the combined components of the wafer or the lid wafer is inoperative.

One other not to be underestimated advantage for the applicability of the method is that a large choice of materials on (high-melting and low-melting) metals for use of the SLID procedure stands. It should be remembered that the adjustment and discontinuation of individual lid chips on the wafer by means of current high-speed bonder can be done at a speed of up to 10 000 such operations (Bonds) per hour, so that by the single alignment of the lid no throughput problem is produced. This is especially true if the individual lid chips According to the invention initially provisionally attached so that the actual connection using SLID is independent of Bonding performed can be.

One another big one The advantage is that after bonding the lid, the sensors or the electrical or micromechanical circuits within the housing already protected are. However, any adjustment structures remain visible on the wafer surface (substrate wafer surface), making an automatic wafer saw can be used with image recognition for separating the chips, what the Singularly simplified.

As already mentioned several times, can instead of simple covers also complex structures, sensors or CMOS circuits be bonded to the substrate wafer, giving the great flexibility of the process once again underlines.

The following is based on the in the 1 and 3 As shown in Fig. 1, the method of producing these circuits will be described in detail again. Following this, the general inventive concept will be clarified again using a flowchart.

For making the lid chips 102 First, it is necessary to sputter an adhesive layer and a diffusion barrier (Ti and TiN) onto the surface of the lid substrate. Then a galvanic seed layer of copper is sputtered on. Then, the structure of the solder ring or of the frame is produced by means of phototechnology, for example, a paint density of 8 microns is used. By means of a subsequent copper electroplating, the first copper layer of the frame can now be deposited with a thickness of, for example, 5 μm. Thereafter, the tin layer is formed on the copper layer of the frame, which is either directly sputtered or produced by means of an additional photolithographic procedure, which may be deposited only spatially discrete on the copper layer. A preferred layer thickness of the tin is between 1 to 3 microns. After removal of the photoresist, a wet etching of the seed layer or the adhesion layer and the diffusion barrier can take place. The required separation of the cover chips according to the invention can then be carried out by clamping the cover wafer onto a sawing foil and singulating the cover by means of a wafer saw.

Of the Substrate wafer is first prepared analogously to the lid wafer, i. First, an adhesive layer and a diffusion barrier of Ti and TiN sputtered onto the surface. On the sputtering of the electroplating seed layer copper is a photolithographic Selection of the solder ring, wherein, for example, a paint thickness of 5 μm used becomes. After exposure of the frame or ring area can by means of Copper electroplating a copper frame of 5 μm in height can be generated. After removal of the photoresist, the seed layer or the adhesive layer and the Diffusion barrier by wet etching be removed. After the frame has been created so completely, can at the same protected by a sensor protected by a sacrificial layer Remove the sacrificial layer to be etched free.

in the Following is assumed that the cover chip first by means of of an adhesive for the time being is attached to the wafer.

To is the lid chip first from the sawing foil to disconnect and attach to a bondhead that is at a temperature of more as 60 ° C is heated, to attach. Thereafter, an adhesive, which melts at 55 ° C, applied (for example bibenzyl or other wax). The application can be done for example by an ink-jet method, wherein because of the temperature of the bonding head, the adhesive on the cover chip first liquid remains.

Thereafter, the adjustment of the lid chip relative to the substrate wafer, so that the solder rings are opposite each other directly. The placement of the lid chip on the cold substrate wafer causes the adhesive (Bibenzyl) to cool below 55 ° C and solidify, so that after releasing the bond head, the lid chip is fixed on the substrate wafer. As already described, the provisional fixation can also be effected by pressing, slight overtemperature (for example 100 ° C.), light friction welding with ultrasound or other temporary bonding methods, in which case the bibenzyl step, as described above, can be dispensed with. By the method described above, all lids on the chips or electrical circuits (possibly only on the well-tested) are first fixed on the substrate wafers by the same method.

After all cover chips are fixed, the capped substrate wafer is transferred into an evacuable soldering oven, in which the lid chips can optionally be pressed onto the substrate wafer with a heatable elastomer and a defined force. Thereafter, a rinse with formic acid can be done to prevent oxidation. After a preliminary heating of the brazing furnace to a temperature of more than 60 ° C, the adhesive evaporates, so that by a subsequent pumping of the brazing furnace potential impurities are largely removed. Thereafter, a heating to the soldering temperature (about 300 ° C at Cu / Sn). Soldering under vacuum requires maintaining the temperature for a predetermined period of time (> 10 seconds to reach the metastable Cu ₆ Sn ₅ phase,> 30 min for the stable Cu ₃ Sn phase). Thereafter, the wafer can be cooled within the vacuum, wherein now prevails within the housing just created a vacuum that substantially corresponds to the vacuum level, as prevailed within the brazing furnace.

During the Further processing can take advantage of the above Advantages sawing the substrate to get the scattered components. The by the casing protected Components can Now with standard methods, such as attaching a Flex tapes or further processed by chip-on-board assembly and wire bonding Be without the sensitive elements inside the housing too compromise.

Derived from exemplary embodiments described in detail, the manufacturing method can be described with reference to the in 5 summarize flowchart shown.

In the preparation step 300 The substrate is prepared with the components to be housed.

In the step of frame generation 302 For example, the frames are generated around the electrical circuits disposed on the substrate or integrated in the substrate.

For the effective packaging of the electrical or micromechanical circuits or components is now in a test step 304 for each of the electrical circuits checked if it is functional. If this is not the case, it will be in an iteration step 306 Checked if there are any other non-tested circuits on the substrate. If this is not the case, the placement process is terminated and it can continue with the soldering or singulation.

If there are more circuits, it will be in the loop 308 and it is checked again whether the next electrical circuit is functional.

Gives the test step 304 in that the electrical circuit is functional, in a connecting step, a cover chip is connected to the substrate at the location of the electrical circuit, whereupon in step 306 It is checked whether further circuits on the substrate have not yet been tested. If this is not the case, the final step 312 the soldering or singulation started. If there are more circuits on the substrate, it will go along a second loop 314 procedure and it is checked again whether the next circuit is functional.

Even though in the preceding paragraphs the application of the inventive concept and the generating according to the invention a housing essentially to the house a bolometer has been described is the inventive concept Naturally as well as any other components that are protected from environmental influences should, applicable. Examples include pressure sensors, microphones, Light sensors and other optical sensors and any kind of Micromechanical elements, such as rotation rate sensors.

Claims (8)

A housing having an electrical circuit, comprising: a first substrate having an electrical circuit; a second substrate disposed above a free volume opposite the first substrate; a frame bounding the free volume between the first and second substrates and comprising a first metal on both sides of a boundary region disposed between the first and second substrates, the boundary region comprising an alloy of the first metal and a second metal; wherein a melting temperature of the second metal is less than a melting temperature of the first metal and a melting temperature of the alloy. casing according to claim 1, in which the first metal is copper and the second metal Tin is. casing according to claim 1 or 2, wherein the first substrate is an integrated circuit having a bolometer. casing according to one of the preceding claims, wherein the second substrate is at least partially wavelength for infrared spectral region is permeable. casing according to one of the preceding claims, in which the free volume has a lower gas density than the environment of the housing. casing according to one of the preceding claims, in which the free volume is enclosed gas-tight. casing according to one of the preceding claims, wherein the second substrate has a smaller area than the first one Substrate. casing according to one of the preceding claims, wherein the first substrate is a tested for operability electrical Circuit has.