WO2006061274A1

WO2006061274A1 - Chip module and method for the production thereof

Info

Publication number: WO2006061274A1
Application number: PCT/EP2005/055199
Authority: WO
Inventors: Ronny Ludwig
Original assignee: Robert Bosch Gmbh
Priority date: 2004-12-07
Filing date: 2005-10-12
Publication date: 2006-06-15
Also published as: DE102004058815A1

Abstract

The invention relates to a chip module, particularly for optical and stress-sensitive measurements, comprising at least the following: a premold housing (1) consisting of a housing body (10) which is made of a plastic or epoxy resin material and provided with a housing edge (16) and a housing bottom (15), in addition to a lead frame (14) which is injected therein and provided with several leads (5) which extend through the housing body (10) and which are bent in such a way that they extend respectively inside (17) the premold housing (1) in bond pads (20) and are laid bare on the lower side (15a) of the bottom of the housing (15) in ball pads (6,7) which are embodied in particular as a ball grid array, also comprising a chip (26) which is fixed inside the premold housing (1), preferably a microstructured sensor chip (26) for optical or stress sensitive measurements and whose contact pads (44) are contacted to the bond pads (20) via wire bonds. According to the invention, it is possible to keep the space requirement on the substrate to be kept as small as possible in comparison with modules having lateral connection spins and mechanical damage of the contacts can also be kept to a minimum, wherein an underfiller can be added for the purpose of completion.

Description

Chip module and method for its production

The invention relates to a chip module with a micromechanically structured sensor element for optical or stress-sensitive measurements, which can be used in particular in the automotive sector, and a method for its production.

Such chip modules may in particular be gas sensor modules with sensor chips for the detection of CO2, which may be e.g. used in CO2-powered automotive air conditioning systems for the detection of leaks.

Micromechanical sensor elements allow for cost-effective production of a standardized design of the measuring structures and accurate measurements. They are housed in suitable housings for protection against damage and contamination as well as for suitable optical alignment. The sensor module formed from the housing and the sensor element can subsequently be mounted on a substrate, e.g. a printed circuit board.

In the case of molded modules, the chips are contacted on leadframes, for example, and the housing is injected or molded around the chips with part of the leadframe. The pins of the leadframe extend laterally out of the housing for contacting and fastening the sensor module as connection pins. For micromechanical sensor chips that are sensitive to stress or need an open access to the chip surface, such as pressure sensor chips or optical sensor chips, such housings are unsuitable. Therefore, premold housings are often used for such sensor chips, in which first a leadframe with several leads in a housing body of a molding material, generally a plastic or epoxy resin, is injected or molded. The premold housings are based on SIP (Single Inline Packages), SOP (Small Outline Packages) or PSOP (Power Small Outline Packages) or similar housing designs. One or more sensor chips are subsequently mounted in the premold housing, eg. B. glued, and contacted with the leads, eg by means of bonding wires.

The leads generally form bonding pads in the interior of the housing body for contacting with the contact pads of the sensor chip and extend laterally outwards through the housing body, where they laterally form protruding connection pins with which the gas sensor module can be fastened and contacted on the substrate. The space required to mount the premold housings on the substrate is determined by the size of the housing and the width of the connection pins. However, the laterally projecting, sensitive connection pins can bend during handling due to mechanical damage, which can lead to problems in the subsequent contacting on the substrate.

Furthermore, sensor chip modules with metal housings, e.g. the TO design, known, which can be further processed in Durchstecktechnik on the circuit boards. However, such an assembly is very time consuming and expensive.

In contrast, the chip module according to the invention and the method for its production have some advantages. According to the invention, a premold housing is formed whose leads form bonding pads for contacting with the micromechanical measurement structure in the interior of the housing and also extend to the bottom of the housing floor. dens are bent such that they form on the underside of the housing exposed, advantageously round, contact areas, so-called ball pads.

Compared with known premold housings with laterally outwardly projecting connection pins, the space requirement on the substrate is thus significantly reduced. Furthermore, according to the invention, mechanical damage to the contacts can be avoided. The ball pads can be directly attached and contacted to the substrate either via printed solder deposits or conductive adhesive deposits, or attached and contacted by the production of solder bumps or conductive bumps similar to flip chip mounting. The solder or conductive adhesive contacts between the premold housing and the substrate can be additionally passivated and protected by filling underfiller material. This also achieves an additional mechanical attachment to the substrate.

The contacting of at least one chip in the interior of the premold housing is advantageously carried out by known wire bonds, which can be safely protected by filling the housing interior with passivation. The leads of the premold housing according to the invention in this case make it possible to make contact with the sensor element via a shoulder region on the inside of the premold housing. On the underside of the housing, a plurality of ball pads may be formed as a ball grid array (BGA), for which purpose advantageously a leadframe with a plurality of differently long leads extending in a lateral direction is used, on which the ball pads in the lateral direction arranged offset to each other and each bent to the underside of the housing bottom.

The invention can in principle be used for any chips, in particular over chips for stress-sensitive or optical applications. Such chips may in particular be micromechanical sensor chips or micromechanical sensor elements with a plurality of chips, which for optical measurements, e.g. B. spectroscopic gas measurements, or z. As stress-sensitive pressure or flow measurements can be used. In principle, but also z. As optical chips or electro-optical chips are used, which require an optical access.

According to the invention, in particular a two-channel gas sensor module can be formed, the z. B. requires six contacts and thus six ball pads, which can be formed as a BGA on the bottom of the housing, without that the housing is to be sized larger.

To produce the premold housing according to the invention, preferably a leadframe strip with correspondingly structured leadframe areas is used, in which the leads are bent in common bend lines or fold lines. The housing body are subsequently encapsulated or molded with a plastic or an epoxy resin and the resulting premold housing, advantageously after assembling the chips, separated by breaking the leads outside the premold housing, so that the individual premold housing in a few finished steps and cost and standardization can be trained.

The invention will be explained in more detail below with reference to the accompanying drawings of some embodiments. Show it:

1 to 3 the production of premold housings according to the invention in a leadframe strip:

1 shows a section of a leadframe strip with a plurality of unbent leadframe areas;

2 shows the detail from FIG. 1 after the bending process in plan view (a) and in cross section (b), FIG. 3 shows the cutout on the leadframe strip after the molding of housing bodies in the bent leadframe areas in plan view (a) and cross-section (b), 4a to f a premold housing according to the invention with six BaII

Pads in bottom view (a), bottom view (b), top view (c), side view (d), and cross sections through longer and shorter leads (e, f). FIG. 5 shows a two-channel gas sensor module first Embodiment of a chip module with the BGA premold package of Figure 4, a hermetically sealed two-channel thermopile chip and glued on the silicon chip cap filter chips with integrated aperture; FIG. 6 shows the gas sensor module from FIG. 5 with additional chip calibration; FIG.

7 a, b show cross sections through the gas sensor module of FIG. 6 along a long and a short lead; FIG.

FIG. 8 shows the gas sensor module from FIGS. 6, 7 after mounting on a substrate;

9a, b show a top view (a) and side view (b) of a dual-channel gas sensor according to another embodiment with the BGA premold housing and a hermetically sealed two-channel thermopile chip with extended housing edge before mounting the cover panel;

Fig. 10 shows the gas sensor module of Fig. 9 with additional, e.g. more transparent, chip assimilation;

11a to c, the gas sensor module of Figure 7 or 8 with additionally mounted cover cover in plan view (a), side view (b) and cross-section (c).

12 shows a cross section through a hermetically sealed two-channel thermopile sensor produced in surface micromechanics, constructed as a chip stack, which can be inserted into the BGA premold housings according to the invention for forming the gas sensor modules of FIGS. 5 to 11.

For the production of premold packages 1, a leadframe Strip 2 produced, of which in Fig. 1 a section is shown; the entire leaframe strip 2 extends in the longitudinal direction, that is, in Fig. 1 to the left and right, over several such cutouts. The leadframe strip 2 is produced by punching a sheet, the z. As copper or a copper-tin alloy, for. B. CuSnβ, advantageously with a coating, for. As a nickel-gold coating exists. Here, in the leadframe strip 2, a pattern of several leadframe areas 3 is punched, which correspond to the later premold housings in the approach. The leadframe areas 3 each have a free space 4 and several, z. B. six parallel in the free space 4 extending leads 5, which are added to a - in Fig. 1 left - end in the leadframe strip 2 and in their other - right in Fig. 1 - Endbereich a ball pad. 6 7, on which, in turn, a narrower area of the lead 5 adjoins to the right, which is free in the free space 4. The leads 5 are of an age-varying length, with their ball pads 6 and 7 offset from one another in the longitudinal direction of the leads 5. As a result, on the one hand when punching the cutouts 4 a better material utilization, ie a lower waste, and on the other hand achieved by the two-dimensional array better space utilization on the bottom of the housing later trainees. The leads 5 can basically be aligned differently in the leadframe strip 2, z. B. in the transverse direction.

According to FIG. 2 a, b, the stamped or structured leadframe strip 2 is subsequently bent by inserting corresponding punches into the leadframe areas 3 from above (or also correspondingly from below). As a result, the leads 5 are bent such that they starting from the ground plane of the leadframe strip 2 in a first bend 8, z. B. substantially at right angles, bent downwards and in turn bent horizontally in at least one further counterbending 9. As the cross section of Fig. 2b and 3b and z. B. also the cross sections of Fig. 4e, f can be seen, in this case a plurality of bending radii can be formed. It is relevant here that the leads 5 in their ball pads 6, 7 run horizontally and the left and right portions of the leads 5 next to the ball pads 6, 7 are bent in contrast upwards, so that the ball pads 6, 7 form the lowest level of the lead frame areas 3.

According to Fig. 3a, b are hereinafter housing body 10 of a

Mold material, for. As plastic or an epoxy resin to the individual lead frame areas 3 gemoldet or injected, so that premold housing 1 are formed, which are separated from the leadframe strip 2 by cutting or punching the leads 5 below. Each premold housing 1 thus has a housing body 10 and a leadframe 14 with a plurality of leads 5. The punching line 12 during cutting or punching of the individual premold housing 1 runs through the leads 5 outside the housing body 10, so that the leads 5 are subsequently electrically separated. The separation of the housing from the leadframe strip is advantageously carried out after the entire construction of the sensor module.

As can be seen in particular from FIGS. 4 a to f, the housing bodies 10 are injection-molded such that they have a housing bottom 15 and a peripheral housing edge 16, whereby an upwardly open interior space 17 is formed. The individual leads 5 are in each case exposed on one shoulder 18 of the housing body 10 in areas serving as bond pads 20 (FIG. 7a), and on the other hand lie in ball pads 6, 7 on the underside 15a of the housing floor 15 below free. The housing edge 16 has a stop edge 22 (FIG. 7a) for the passivation medium to be introduced later, as will be described below.

At least one microstructured chip is subsequently glued into the premold housing 1. FIGS. 5 to 7 show a first embodiment of a two-channel gas sensor module 24, in which a microstructured, shown in more detail in FIG. 12, in the preform housing 1

Sensor element 23 is glued, which is formed as a chip stack of a sensor chip 26, a cap chip 28 and two filter chips 30 a, b. in this connection is the sensor chip 26 on the housing bottom 15 of the gas sensor module 24 by means of an adhesive layer 25, for. As a conventional chip adhesive attached.

Two optical measuring structures 32 a, b are formed in the surface of the sensor chip 26 in surface micromachining (OMM), each measuring structure 32 a, b each having a membrane 33, a cavern 34 underneath the membrane 33 and a thermopile on the membrane 33 -Structure

35 comprises interconnected interconnects formed of materials having different Seebeck coefficients and extending from the membrane 33 to the bulk material of the sensor chip 26. On the thermopile structure 35 of each measuring structure 32 a, b is an absorber layer

36 of an infrared radiation absorbing material, for. As a metal oxide applied. On the underside of the cap chip 28, a cavern 38 is formed, which serves as a common sensor space for both measuring structures 32 a, b and includes a vacuum. The cap chip 28 is in this case on the sensor chip 26 in a vacuum-tight connection, for. B. Sealglas- connection 40, fixed so that the vacuum of the cavity 38 is sealed from the outside. The two filter chips 30 a, b are fastened on the upper side of the cap chip 28 in each case by means of an adhesive layer 42 transparent to IR radiation.

The two optical measuring structures 32a, 32b of the dual-channel sensor element 23 serve for a first measurement and a reference measurement and are of identical design; the filter chips 30a, b bonded to the common cap chip 28 have different absorption characteristics. In this case, the first filter chip 30a selectively absorbs infrared radiation in the CO2-relevant wavelength range at approximately 4.26 μm and the second filter chip 30b in a different reference wavelength range at, for example, 3.9 μm. Incident IR radiation thus passes through the filter chips 30a, b, the transparent adhesive layers 42 and the common, for IR radiation transparent silicon cap chip 28, the cavern 38th and reaches the absorber layers 36 of the respective measurement structure 32a, b. Depending on the incident IR radiation, it heats up, so that its temperature increase is detected by the particular thermopile structure 35 underneath as a thermoelectric voltage and corresponding measuring voltages are generated. The conductor tracks of the thermopile structure 35 are connected to contact pads 44 (or bond pads) on the upper side of the sensor chip 36 outside the cap chip 28, so that the measurement voltages generated in the two optical measurement structures 32 a, b can be read out via the contact pads 44 , and subsequently - in a manner known per se - from a difference or a ratio of the measurement signals, the content of CO2 in a measuring space between a radiation source, not shown, and the gas sensor module 24 can be determined.

The sensor elements 23 from the chips 26, 28 and 30 a, b are already produced at the wafer level in a conventional manner by the sensor chips 26 structured, the cap chips 28 etched and the respective wafer are mounted on each other, whereupon the sensor elements 23 from the wafer stack to be isolated. The respective sensor elements 23 is glued to the housing bottom 15 via the adhesive layer 25, then the filter chips 30a, b are glued to the cap chip by means of the IR-transparent adhesive, subsequently the contact pads 44 of the sensor chip 26 to the bond pads 20 of the leads 5 via wire bonds 46 contacted and in the housing interior 17 of the premold housing 1 a passivation agent 50, z. As a common gel poured. The passivation agent 50 in this case reaches the peripheral stop edge 22, which is arranged slightly below the surface of the filter chips 30a, 30b, so that the passivation means 50 does not cover the surface of the filter chips 30a, b.

The gas sensor module 24 according to the invention has no laterally outwardly projecting connection pins, but only the ball grid array (BGA) forming ball pads 6 and 7, via which the gas sensor module 24 below on a substrate 52, for. B. a printed circuit board or a Ke- ramiksubstrat, fastened and contacted. For this purpose, as electrically conductive connecting means regions 54 and ball contacts solder depots of solder material in stencil printing or corresponding conductive adhesive deposits from z. B. silver conductive adhesive applied in screen printing on the circuit board 52. The assembly is thus carried out by gluing or soldering on the substrate 52. The connecting means regions 54 are in this case received completely below the gas sensor module 24, so that no further lateral space on the substrate 52 is required. They are further protected against direct mechanical damage. In addition, in the intermediate space 56 between the gas sensor module 24 and the substrate 52, ie around the connecting means regions 54, an indicated underfill material 57 made of an electrically non-conductive material, introduced to protect the connecting means 54 from environmental influences and the mechanical connection stability of the housing to increase the substrate.

FIGS. 9 to 11 show a two-channel gas sensor module 58 according to a further embodiment, with an otherwise corresponding structure such as the gas sensor module 24 of the first embodiment on the housing body 10 of the premold housing 1 on two opposite sides an upwardly projecting bending edge 60 of z. B. in addition 0.5 mm in length is formed. The bending edge 60 is used to attach a cover cap 62 made of metal of z. B. 150 microns thickness. In this embodiment, a passivation agent 50, in particular a silicone gel, can be used that is permeable and softer than the passivating agent used in the first embodiment. A protection of the interior 17 of the premold housing 1 and the passivation means 50 introduced therein takes place via the attached cover 61, which is fixed to the premold housing 1 by staking the bending edge 62 according to FIG. 10 a, b. In addition, at the other two sides of the housing 1, on which no bending edge 60 is formed, cover edges 64 of the diaphragm cover 62 are angled downward by 90 °, so that an additional lateral fixation is achieved. The diaphragm cover 62 is thus fixed recorded and fixed, so that formed in it apertures 66 a, b above the two filter chips 30 a, b are positioned. The diaphragm cover 62 thus serves, on the one hand, to protect the interior 17 of the premold housing 1, in particular also when using the soft passivation agent 50, so that no or hardly any dirt can penetrate, and, on the other hand, as an optical diaphragm or numerical aperture the optical measuring structures 23 a, b to keep stray radiation away. Thus, in the second embodiment, filter chips 30 without aperture coating can be used.

Claims

claims

1. Chip module, in particular for optical or stress-sensitive applications, which comprises at least: a premold housing (1) which has a housing body (10) made of a plastic or epoxy resin material with a housing edge (16) and a housing bottom (15) and a leadframe (14), which is injected into the housing body (10) and has a plurality of leads (5), which extend through the housing body (10) and are bent in such a way that they each lie in the interior (17) of the preform housing (1). in bonding pads (20) and on the underside (15a) of the housing bottom (15) in ball pads (6, 7), and at least one chip (26, 28, 30a, b) mounted in the premold housing (1) and contact pads (44) which are in contact with the bond pads (20) of the leads (5) via wire bonds (46) extending through the interior (17) of the premold housing (1).

2. Chip module according to claim 1, characterized in that the premold housing (1) by a surface mount technology - method can be mounted.

3. Chip module according to claim 1 or 2, characterized in that in the interior (17) of the premold housing (1) a Passivie- rungsmittel (50) is introduced, the bonding pads (20) of the leads

(5) completely surrounds the contact pads (44) of the chip (26) and the wire bonds (46).

4. Chip module according to claim 3, characterized in that on the inside of the housing edge (16) has a circumferential stop edge (22) for limiting the filling level of the passivation means (50) is formed.

5. Chip module according to one of the preceding claims, characterized in that bonding pads (20) on the top of a shoulder (18) of the housing edge (16) are formed and the leads (5) of the bond pads (20) starting in a first bending edge ( 8) bent down and in at least one other bending edge (9) in front of the ball pads (6, 7) are in turn counter-bent.

6. Chip module according to one of the preceding claims, character- ized in that the leads (5) extend from one side parallel through the premold housing (1) and formed to the ball pads (6, 7) of different lengths such in that the ball pads (6, 7) on the underside (15a) of the housing bottom (15) are offset from one another in the lateral direction and the longitudinal direction.

7. Chip module according to claim 6, characterized in that the leads (5) are formed alternately shorter and longer and a ball grid array of mutually offset ball pads (6, 7) aufwei- sen.

8. Chip module according to one of the preceding claims, characterized in that on the premold housing (1) a lid (62) placed and hot-staked by moving a projecting bending edge (60) of the housing body (10).

9. Chip module according to one of the preceding claims, characterized in that it is a sensor module (24, 58), wherein in the premold housing (1) a sensor element (23) with at least one microstructured sensor chip (26) is recorded for optical or stress-sensitive measurements ,

10. Chip module according to claim 9, characterized in that the sensor element (23) a chip stack of the sensor chip (26), a cap chip (28) and at least two on the cap chip (28) attached filter chip (30a, b) for the selective absorption of Infrared radiation of different wavelength ranges, wherein on the sensor chip (26) at least two optical measuring structures (32a, b) for measuring the through the filter chips (30a, b) reached infrared radiation are formed.

11. Chip module according to claim 9, characterized in that it is a

Sensor module with a stress-sensitive sensor chip (26) for a pressure measurement or flow measurement is.

12. A method for producing a chip module (24, 58), with at least the following steps:

Providing a leadframe strip (2) with a plurality of leadframe areas (3), each having a plurality of leads (5), each with a ball pad (6, 7), at one end in the leadframe strip (2) and are free at the other end,

Bending the leads (5) of each lead frame area (3) such that each lead (5) has a top area for a bond pad (20) and a bottom area for a ball pad (6, 7); 10) around the bent leadframe areas (3) such that the ball pads (6, 7) at the bottom

(15a) of the housing bottom (15) of the housing body (10) and the upper portions of the lead (5) each form a bonding pad (20) on a shoulder (18) of the housing body (10), securing at least one chip (26) in the premold housing (1),

Contacting the chip (26) with the bond pads (20) of the leads (5), and Separating the premold housings (1) from the leadframe strip (2) by severing the leads (5) outside the housing body (10),

13. The method according to claim 12, characterized in that formed between contact pads (44) of the chip (26) and the bond pads (20) of the leads (5) wire bonds (46) extending through the interior (17) of the premold housing ( 1), and subsequently in the interior (17) of the premold housing (1) passivation medium (50) is input, which the contact pads (44) of the

Chips (26), the bond pads (20) of the leads (5) and the wire bonds (46) covered.