This application claims the benefit of the filing date under 35 U.S.C. § 119(a)-(d) of German Patent Application No. 102020215388.4, filed on Dec. 4, 2020.
The present application relates to a chip module, to the use of such a chip module, to a test arrangement for testing a contacting of the chip module, and to a test method for testing the contacting of the chip module.
Semiconductor components usually use a front side of a wafer or chip for the arrangement of electrically active elements. These semiconductor components are mounted on a chip carrier and electrically contact the chip carrier. Many of these semiconductor components require an electrically conductive contact to be made on the rear side of the chip. To ensure a sufficiently good electrical contact, wafer backs are usually metallized, very often by a metal sandwich layer with a final gold surface.
The connection between the chip and the chip carrier has to fulfill two essential functions. In this case, on the one hand, a sufficient mechanical connection must be established that guarantees the strength, in particular the adhesive strength, under the conditions of use of the component. Furthermore, this connection should ensure a stable electrical connection under conditions of use. The combination of these two functions creates high demands on the adhesive connection or soldered or sintered connection.
A chip module includes a chip having a front side and a rear side, a chip carrier having an upper side facing the chip, a contact layer formed of an electrically conductive material and arranged on the upper side of the chip carrier between the rear side of the chip and the upper side of the chip carrier, and an electrically conductive adhesive arranged on an upper side of the contact layer facing the chip. The electrically conductive adhesive connects the upper side of the contact layer and the rear side of the chip. The contact layer has a plurality of regions electrically insulated from each other and each electrically connected to the chip by the electrically conductive adhesive.
The invention will now be described by way of example with reference to the accompanying Figures, of which:
The present invention shall be explained in more detail hereafter with reference to the figures. Same parts are provided with the same reference numerals and the same component names. Furthermore, some features or combinations of features from the different embodiments shown and described can in themselves represent solutions that are independent according to the invention. Recurring features are provided with the same reference symbols.
The contact layer 3 comprises at least three, and in the shown embodiment four regions 3A, 3B, 3C, 3D, that are electrically insulated from each other in the shown embodiment. In the present example, the regions 3A to 3D that are insulated from each other are rectangular. In other examples, these regions 3A to 3D can also have other shapes, for example square, circular, elliptical or combinations of such shapes. The regions 3A to 3D each protrude beyond the chip 1. In other embodiments, the contact layers 3 can have more than four mutually insulated regions. The regions insulated from each other can also be referred to as contact regions.
In one embodiment, the chip 1 can have a length of at least 1 mm, at least 1.5 mm, or at least 2 mm. Additionally or alternatively, the chip 1 can have a length of at most 200 mm, at most 100 mm, or at most 50 mm. However, chips 1 with even greater dimensions can also be processed. In one embodiment, the chip 1 can have a width of at least 1 mm, at least 1.5 mm, or at least 2 mm. Additionally or alternatively, the chip 1 can have a width of at most 200 mm, at most 100 mm, or at most 50 mm.
The chip 1, in the embodiment shown in
In the present case, the chip 1 can be understood to mean a microelectronic component, in particular a semiconductor chip or a microsystem. The chip 1 has a front side 11 and a rear side 12. The front side 11 usually carries the active semiconductor structures. The chip 1 can have electrical contacts on its rear side, for example for supplying an electrical component or microsystem integrated in the chip with a voltage, and/or for communicating with the electrical component and/or microsystem. Additionally or alternatively, the chip 1 can have further electrical contacts on its front side.
In the present example, the chip carrier 2 comprises FR4 or its derivatives. FR4 is a printed circuit board base material, such as a glass-reinforced epoxy laminate material. An embodiment consisting of ceramic or comprising ceramic is also possible. Through-holes which allow a through-hole plating 31 are provided in the chip carrier 2. In each of the mutually insulated regions 3A to 3D, the contact layer 3 has a plated-through hole 31 which connects a contact surface 32, which is arranged on the upper side 21 of the chip carrier 2, to an underside 22 of the chip carrier 2. This can have the advantage that each of the regions 3A to 3D insulated from each other can be controlled electrically independently of the others via the plated-through hole 31. On the underside of the chip carrier 2, the contact layer 3 has a soldering surface 33 at the lower end of the plated-through hole 31, as shown in
In one embodiment, the chip 1 and the contact layer 3 are arranged centered in such a way that a surface center point of the upper side of the contact layer 3 is at a minimum distance from a surface center point of the rear side 12 of the chip 1. The contact layer 3 comprises the regions 3A-3D that are electrically insulated from each other, such that the surface of the contact layer 3 is defined by outer edges of the regions that are electrically insulated from each other. The center point of a surface of the contact layer 3 defined in this way can thus lie in one of the regions 3A-3D insulated from each other, or also in a region that lies between the regions 3A-3D insulated from each other.
An electrically conductive adhesive 4 is arranged on an upper side of the contact layer 3—more precisely, on each of the upper sides 321 of the respective contact surfaces 32. This is shown in
The contact layer 4 can, for example, comprise gold and/or other noble metals and/or other metals. The electrically conductive adhesive 4 can comprise, for example, one polymer or several polymers, for example epoxy resin, acrylate, silicone, polyurethane and/or esters. The electrically conductive adhesive 4 can comprise silver particles and/or one or more other conductive substances, for example graphite. The conductive substances can in particular be embedded in the polymer(s).
The housing 5 as shown in
In
The chip module can comprise one or more further chips 1. The features of the present application which are described with regard to one of the chips 2 can be applied analogously to the at least one further chip, or the plurality of further chips. In one embodiment in which the chip module comprises a plurality of chips 1, the chips 1 can have different characteristics. For example, one or more sensor chips, ASICs for signal evaluation, one or more temperature sensors, and/or one or more LEDs can be provided as a light source. Chips of the same type can also be built into a chip module.
In one embodiment, the chip module can comprise passivations. The chip module can be protected from environmental influences by passivation. Passivations can be, for example, lacquers, conformal coatings, potting, glob tops, underfills or mold compounds that are applied over the entire surface or a portion thereof. A conformal coating adapts to the underlying surface structure, a glob top covers or completely encases bond connections or chips, and can be formed of a plastic material. An underfill is a polymer that flows between the chip 1 and the chip carrier and bonds them together; the underfill can serve as additional mechanical fixation and/or to fill cavities.
The chip 1 shown in
In the case of very small chips 1 (especially chips with an edge length of less than 2 mm), it may be technologically more favorable to make the contact layer 3 larger than the chip 2. In the case of very large chips, on the other hand, it can be advantageous to select the contact layer edge length to be less than the chip edge length, so that the different expansion behavior has less of an effect.
The contact layer 3′ of
The chip 1 is also shown in
A sensor can comprise the chip module according to the embodiments described above. The chip module according to the aforementioned embodiments can in particular be used in an optical sensor, in particular a LIDAR sensor. These can be used, for example, in vehicle information or safety systems, for example distance warning systems, and in the field of autonomous driving.
It should be noted that the test arrangements of
Each of the test arrangements of
First, a test current 8 is measured between the first and the second connection element 7, for example the first and the second contacting needle 71, 72. The measured test current 8 can then be compared with a predefined threshold value. If the measured value is greater than the threshold value, this indicates a defect. Further test currents 8 can be measured between further connection elements 7. The test currents 8 can each be compared with a threshold value or with each other. Defects are localized by assigning the measured values to the position of the contact layer 3.
Provision can be made to define a tolerance range around a determined average value. It can be provided that test currents 8 which are outside the tolerance range indicate a defect. A local region of the chip 1 can be assigned to these determined test currents 8. A warning signal can indicate that the localized region of the chip 1 has a defective contact.
A resistance can first be calculated from a measured test current 8. The calculated resistance can be compared with a threshold value. A deviation from the threshold value can indicate a defect in the corresponding contact. A warning signal can be output to a higher-level system or to a user. By way of example, the limit is 100 Ω.
The conductive adhesive 4 can in particular have a threshold value in the low-ohm range. In the event of a failure, the threshold value of the electrical contact can be in the mega- or gigaohm range. Resistances of the electrical contacts on the rear side of the chip 1 are usually in the lower ohm range. Depending on the chip area on the rear side, these are typically often less than 1 ohm.
If such a connection to the rear side of the chip fails, the resistance can increase by a factor of 1000 to 1,000,000 or more. Such an increase can be easily detected electronically. When graphite or aluminum-filled adhesives are used, they are typically less conductive. They are then mostly in the kilo-ohm to mega-ohm range. Threshold values can also depend on environmental influences, for example moisture.
The threshold value can therefore be product-specific. In particular, the threshold value can be at least 0.1 Ω, at least 0.5 Ω, or at least 1 Ω. The threshold value can be less than 100 MΩ, less than 100 kΩ, or less than 100 Ω.
Errors can be predicted by repeating and comparing measurements. For this purpose, for example, a first measured test current can be compared with a second test current measured at a later point in time. The first and the second test currents were measured between the same insulated regions or between the same insulated region and the electrical contact element of the chip carrier.
The test method can in particular be suitable for testing the contacting during and/or after the manufacture of the chip module. In this case, contact resistances of at least two or more of the contact regions 3A to 3D insulated from each other can be compared with each other or with a good/bad value by a current-voltage measurement. This measurement can be integrated into the manufacturing process as a sample measurement. It can also be provided that during the manufacturing process of the chip module, all contacts or substantially all contacts are checked according to the test method.
The test procedure can be carried out as part of the quality control of the chip module. After completion of the module, in what is usually called the final test, the contact resistances of at least two or more of the insulated contact surfaces can be compared with each other or with at least one threshold value, for example in the form of a good/bad value, by a current-voltage measurement with a suitable contacting and measuring device, for example the test arrangement described. This measurement can be integrated into the quality control process as a sample measurement. It can also be provided that, during the quality control of the chip module, all contacts or substantially all contacts are checked in accordance with the test method.
The test procedure can be carried out as part of reliability tests for the purpose of developing, changing, qualifying, and quality assurance of the chip module. With suitable contacting and measuring devices, in particular the test arrangement described above, contact resistances of at least two or more of the insulated contact surfaces can be detected by a current-voltage measurement. This can take place as a function of various parameters such as time, temperature, humidity, etc. The measured value detection can take place continuously.
In an embodiment, the test method described can be applied while the chip module is being used, for example in a LIDAR sensor. The measured value detection can take place continuously. A warning can be sent to the higher-level system if the specified threshold values are exceeded above or below. This can be particularly advantageous for safety-relevant systems, for example in vehicle safety systems. For example, failures of individual contacts of the chip module can be detected and localized, preferably in real time, and the warning signal can be used to signal a failure or loss of quality of certain contacts to a user or a system. In addition to a suddenly occurring malfunction of the chip module, the test method can therefore also detect an incipient malfunction of the chip module.
The present invention improves the stability and reliability of the connection between the chip 1 and the chip carrier, and/or creates a possibility of checking the state of this electrical and mechanical connection and, in particular, of monitoring it permanently.
The essential function of secure rear-side contacting of a chip 1 can be tested not only in the manufacturing process itself, but this test can be carried out permanently in an application—i.e., while the chip module is being used, for example in a motor vehicle or a drone, and again, for example in a LIDAR sensor. In the case of safety-critical applications in particular, this can offer the possibility of detecting a failure at an early stage and reacting accordingly.
Number | Date | Country | Kind |
---|---|---|---|
102020215388.4 | Dec 2020 | DE | national |