Interconnect substrate having integrated circuit for programmable interconnection and sample testing

Abstract: An interconnect substrate has formed thereon a first plurality of conductive leads (108-1...108-J) and a second plurality of conductive leads (109-1...109-K). A plurality of cells (106-1,1...106-J,K) are formed in the substrate, each cell having a number of bonding pads (107-1...107-M) formed on the surface of the substrate above the region of the substrate in which the cell is formed, thereby to allow a plurality of integrated circuit chips and electrical components to be attached to the substrate and electrically connected to the cells. Devices and programming elements in the substrate or in integrated circuits mounted on the substrate allow selected connections to be formed between selected ones of the conductive leads to be connected electrically thereby to allow selected components mounted on the substrate to be electrically interconnected. Other devices in the substrate or in integrated circuits mounted on the substrate allow testing of the components mounted on the substrate to determine their performance and the checking of the integrity of the connections formed between conductive leads.

Description: This invention relates to an interconnect substrate with circuits mounted on the substrate for the electrical programming in the field of interconnects on the substrate and for the testing of the integrity of the interconnects, the electronic components on the substrate and the system function for hybrid circuits and multichip modules. Hybrid circuits and multichip modules are commonly used to connect electronic components for applications in instruments, computers, telecommunication equipment and consumer electronic products which require higher density and performance than the capabilities of printed-circuit boards. Typically, an engineer will design a hybrid circuit or a multichip module to carry the types of electronic components (including integrated circuits, transistors, and discrete components such as resistors, capacitors and inductors) necessary to implement the desired electronic function and to fit in the space available for the product. Consequently, each hybrid circuit or multichip module typically is custom designed. To design a custom hybrid circuit or a multichip module is expensive, takes time and requires custom tooling and the fabrication of prototype interconnect substrates. If errors are found in the prototypes, then the interconnect substrate must be redesigned. Such a process often delays the planned introduction of a new product. Bare dice, surface-mounted packages and electronic components are used with hybrid circuits and multichip modules, to provide high density. Shorter connection traces result in lower capacitances to drive shorter signal propagation delays, and higher performance. Testing of the integrity of the interconnects and the electronic components in the hybrid circuits and multichip modules is rather difficult. Attaching the probes of oscilloscopes and logic analyzers to observe the waveforms on the various pins of the electronic components during operation require microprobing of fine lines and pads which is difficult. Many of the interconnects to be tested are imbedded and difficult to test. The use of test pads to access some of the imbedded traces takes area and often unintentionally overlooks important traces. The testing, diagnosis and debugging of hybrid circuits and multichip modules are complicated, time consuming and often delay the planned product introduction. In the prior art, universal interconnect substrates which can be programmed to provide any desired interconnection pattern are described in US patents No. 4,458,297; No. 4,467,400; No. 4,487,737 and No. 4,479,088. The universal substrates in the prior art used interconnect architecture which could not be programmed or tested from external leads and which required probing of internal pads to program the connections or to test the integrity of the interconnects or the electronic components on the substrate. To optimize the number of internal pads for the programming and testing of the interconnects, prior art architecture has interconnects with excessive lengths and parasitic capacitances which reduced the speed of the connections on the substrates. The difficulties in testing and programming such universal substrates are time consuming and often increase the product development time and expenses. Other prior art (an article entitled "Active Substrate System Integration" by Wooley et al, at the Center for Integrated Systems at Stanford University, copyrighted 1987 by the IEEE) discloses the potential use of active circuits in the substrate to implement drivers, receivers, repeaters and power distribution circuits. Such circuits are custom designed for each case and are active during the operation of the electronic components and chips on the substrate to implement the desired function. Disclosed in earlier European Patent Application 90310252.3 filed September 19, 1990 and published as EP-A-419232 is a printed circuit board of unique configuration combined with one or more special programmable integrated circuit chips (often called "programmable interconnect chips" or "PICs") to provide a user programmable printed circuit board capable of being used to provide any one of a plurality of functions. The active circuits in the programmable interconnect chips also provide test ports which offer powerful structures for testing the integrity of the interconnects, the electronic components and the system function. The field programmable printed circuit board described in EP-A-419232 substantially reduces the cost associated with developing complex electronic systems by providing a standard PC board configuration which is easily and economically manufactured. As disclosed in EP-A-419232, the designer of electronic systems utilizing the standard programmable PC board described therein will also utilize computer aided design software to determine the optimum placement of the electronic components on the programmable PC board and to determine the configuration of the programmable interconnect chip or chips to properly interconnect the electronic components so as to yield the desired electronic system. International Patent Publication WO 90/04233 discloses an interconnect structure in which logic chips mounted on one or more circuit boards are programmably interconnected by interconnect chips for simulating a desired electronic design. The interconnect structure contains stimulators and samplers. A stimulator is a bit of storage controlled by a host computer for driving a net in the design being simulated. A sampler is a bit of storage controlled by the host computer for receiving a net in the design. The simulators and samplers are formed with flip-flops contained in the logic chips. In the present application, interconnect substrates for hybrid circuits and multichip modules with circuits mounted on the substrate are disclosed. These circuits enable the engineer by using external leads to electrically program the interconnects in the field and to connect any sets of nodes on the substrate to external test ports to test the integrity of the interconnects and the electronic components on the substrate and the system function. These circuits provide the benefits of the field programmable printed-circuit boards for applications requiring the density and performance of multichip modules and hybrid circuits. During normal operation these circuits mounted on the substrate can be disabled and the connections of the interconnects on the substrate provide the desired function. In accordance with this invention there is provided a structure comprising: an interconnect substrate; a plurality of component contacts formed over the interconnect substrate for receipt of electronic components; a plurality of electrically conductive traces formed over the interconnect substrate, each conductive trace being electrically connected to a corresponding one of the component contacts; and at least one programmable integrated circuit mounted over a selected portion of the interconnect substrate, the or each programmable integrated circuit containing (a) a plurality of electrically conductive leads each being electrically connected to a corresponding one of the conductive traces, (b) programmable means for selectively electrically interconnecting the conductive leads so as to programmably interconnect selected ones of the conductive traces, and (c) active test devices for testing the conductive leads and/or the conductive traces and/or the electronic components received by the component contacts, the active test devices comprising sampling means to sample test data provided from the electronic components.. The invention thus provides an architecture of interconnects on a substrate suitable for hybrid circuits and multichip modules with circuits mounted on the substrate to allow the user to electrically program the interconnects in the field with external leads and without the need to use fine probes to access internal fine lines or pads on the substrate. Circuits mounted on the substrate enable any set of nodes on the substrate to be connected to a test port to functionally test any component on the field programmable hybrid circuit or multichip module as well as to test the internal nodes and operation of the module and the interconnect integrity of the field programmed hybrid circuit or multichip module. The field programmability and testability features and ports of the resulting hybrid circuit or multichip module are enabled by mounting programmable interconnect chips ("PICs") on the substrate which contains multilayer interconnects and pads. These circuits are activated, as needed, to implement the programming in the field, or the testing functions. During normal operation, these active circuits can be disabled. An embodiment of this invention uses an interconnect substrate formed of any one of a number of materials to contain a plurality of conductive traces which are routed to a portion of the interconnect substrate on which one or more programmable interconnect chips are to be mounted. The interconnect substrate can for example comprise a semiconductor material such as silicon, metal (with appropriate insulating layers formed thereon) or ceramic. The structure of the conductive traces formed on the interconnect substrate is as described in EP-A-419232. The interconnect substrate can contain a single or multiple layers as described in EP-A-419232. The PIC mounted on the interconnect substrate performs the functions of programming and testing. Bonding pads on the substrate are distributed in a regular pattern to make the bonding pads as general purpose as possible to be used with different dice and electronic components. Moreover, the pad layout is independent of die attach and bonding schemes (for example, wire bonding, solder bumps or TAB). The invention is further described below, by way of example, with reference to the accompanying drawings in which: Figure 1 illustrates an interconnect structure in accordance with the invention for use in implementing programmable hybrid circuits and multichip modules; and Figures 2a and 2b illustrate the PIC with active circuits to implement software-controlled bed-of-nails test structure for in-circuit testing and to implement an imbedded logic analyzer test structure respectively. The following description is illustrative only and not limiting. Other embodiments of this invention will be obvious to those skilled in the art in view of this description. Figure 1 illustrates an embodiment of the interconnect substrate 1001 of this invention where the active circuits for the electrical programming and the testing of the interconnects is implemented with a programmable interconnect chip ("PIC") 1005 mounted thereon. The structure of this interconnect substrate is in arrangement and function identical to that shown in Figure 1 of EP-A-419232 referred to above. Substrate 1001 could comprise any one of a number of materials, such as silicon, metal or ceramic, provided the materials would allow the electrical leads 1003-r,c (where r equals the number of rows of conductive pads on the interconnect substrate and c equals the number of columns of conductive pads on the interconnect substrate) to be electrically isolated from each other and thereby avoid short circuits or other unwanted electrical connections between the conductive leads 1003-r,c. Typically substrate 1001 can comprise a single layer or multiple layers of support material. Shown in Figure 1 are two layers 1001-1 and 1001-2 of support material. other numbers of layers can be used if desired. Each layer 1001-i is fabricated of, for example, a rigid support material such as a ceramic, a metal with appropriate insulation formed on the surface thereof, or silicon with an appropriate insulation layer formed on its surface. The leads 1003-r,c comprise any appropriate conductive material such as, for example a metal, a silicide, doped conductive silicon or other appropriate conductive material. Formed on the center of substrate 1001 or in an appropriate location on the interconnect substrate 1001 is the programmable interconnect chip 1005. Chip 1005 contains a plurality of devices (for example, programmable devices, diodes or transistors) which can be programmed by a user to interconnect selected ones of leads 1003-r,c so that the components mounted on the interconnect substrate 1001 are properly interconnected into the desired circuit. The PIC chip 1005 can contain any appropriate number of interconnect structures and in fact can be one of several such PIC chips. A more detailed description of this chip is given in the above referenced EP-A-419232. Figures 2a and 2b illustrate PIC 1005 of Figure 1 with examples of circuits and structures for testing the integrity of the conductive interconnects, the electronic components and the system function. Figure 2a shows the block diagram and active circuits on the PIC 1005 to implement a software-controlled bed-of-nails test structure. A typical cell 406-s,t on the PIC 1005 with a configuration of pads 407-m is shown. Each pad 407-m is connected to a corresponding conductive segment 409-m. Active transistors 403-m and selection/multiplexing circuits 405B also formed in PIC 1005 select any sets of pads 407 and connect them to an internal bus 414. In Figure 2a, breaklines are included to indicate that the PIC 1005 is only partially shown with interior portions of PIC 1005 removed for clarity. Thus, the signals applied on the control port can select any sets of pads 407 and connect them to the external leads of the test port. Hence, the user can observe the real-time waveforms or force input signals on any sets of pads connected to the test port, making it equivalent to a software-controlled bed-of-nails test structure. Figure 2b shows the block diagram and active circuits on the PIC 1005, to implement an imbedded logic analyzer test structure. According to the signals applied to the control port of the PIC 1005, key information supplied by the user is stored in the trigger data register 441. When the data sampled from the pads 407 by the sampling gates 440 in response to the sampling clock signal on lead 445 compare with the key information in the trigger data register 441, the comparator 442 initiates the memory controller 444 to start the memory address counter 446 for the storage memory 443 to store the sampled data from the pads 407 by the sampling gates 440. After suitable sampled data is stored in the memory 443, the data is shifted through the test port externally to display and analyze. While conductive leads in different layers may be interconnected, those skilled in the art will recognize that conductive leads in the same layer can be connected together using an antifuse technique. To do this, a conductive lead that has been split into two or more segments can be rejoined together by applying a programming voltage between the terminals of a programming element such as an antifuse connected to the ends of the segments of the conductive lead. This programming voltage would then cause the programming element to form a conductive path between these two ends of the conductive track. Alternatively, various segments of adjacent conductive leads can be interconnected by programming elements connected between sections of these adjacent segments. These programming elements can, in one embodiment, consist of sections of segments deliberately formed close together by, for example, introducing curves or bends in the leads. As noted above, an embodiment of this invention uses an interconnect substrate formed of any one of a number of materials to contain a plurality of conductive traces which are routed to a portion of the interconnect substrate on which one or more programmable interconnect chips (PICs) are to be mounted. The interconnect substrate can, for example, comprise silicon (intrinsic or appropriately covered with an insulating layer), metal (with appropriate insulating layers formed thereon) or ceramic. The structure of the conductive traces formed on the interconnect substrate is as described in EP-A-419232. The interconnect substrate can contain a single or multiple layers of conductive traces as described in EP-A-419232. The PIC mounted on the interconnect substrate performs the functions of programming and testing. The PIC, typically an integrated circuit, consists of conductive leads and programming elements such as antifuses, for interconnecting selected leads. The PIC may also include, in addition, transistors and other circuit components to assist in the programming, but these transistors and other circuit components may be excluded to simplify and reduce the cost of the PIC. While the invention has been described in conjunction with a PIC containing a first level of conductive leads and a second level of conductive leads, or just a single level of conductive leads, of course any number of levels of conductive leads appropriate and compatible with the processing technology can be used. While a first set of conductive leads and a second set of conductive leads are typically placed substantially orthogonal to each other, it should be understood that the first and second sets of leads can, if desired be oriented in a substantially different direction rather than being substantially orthogonal to each other and the invention will still be capable of being implemented. Other embodiments of this invention will be obvious to those skilled in the art in view of this description.

Claims: A structure comprising: an interconnect substrate (1001); a plurality of component contacts (1002-1,1...1002-6,1) formed over the interconnect substrate for receipt of electronic components; a plurality of electrically conductive traces (1003-1,1...1003-6,1) formed over the interconnect substrate (1001), each conductive trace being electrically connected to a corresponding one of the component contacts (1002-1,1...1002-6,1); and at least one programmable integrated circuit (1005) mounted over a selected portion of the interconnect substrate (1001), the or each programmable integrated circuit (1005) containing (a) a plurality of electrically conductive leads each being electrically connected to a corresponding one of the conductive traces (1003-1,1...1003-6,1), (b) programmable means for selectively electrically interconnecting the conductive leads so as to programmably interconnect selected ones of the conductive traces, and (c) active test devices (440-446) for testing the conductive leads and/or the conductive traces (1003-1,1...1003-1,6) and/or the electronic components received by the component contacts, the active test devices comprising sampling means (440, 445) to sample test data provided from the electronic components. A structure as claimed in claim 1 wherein the active test devices (440-446) further comprise means (441-444, 446) to process the sampled test data. A structure as claimed in claim 1 or 2 wherein at least one of the conductive leads is divided into at least two separate conductive segments in a line with one another. A structure as claimed in any one of claims 1 to 3 further including the electronic components received by the component contacts. A structure as claimed in any one of claims 1 to 4 wherein in one of the at least one programmable integrated circuit, the sampling means (440 and 445) is operable to sample selected ones of the electronic components to determine the states of the selected electronic components and, in that programmable integrated circuit, the active test devices further comprise: first means (441) for storing data input into that programmable integrated circuit by a user; means (442) for comparing the data sampled from the selected electronic components to the data stored in the first means (441) for storing data to determine whether or not a match between the sampled and stored data has occurred; second means (443) for storing the data available from the selected electronic components in response to a match being detected between the data stored in the first means (441) for storing and the sampled data; and means for outputting the data stored in the second means for storing. A structure as claimed in any one of claims I to 5 wherein there are multiple layers of the conductive traces (1003-1,1...1003-6,1).

Inventors: MOHSEN AMR M, MOHSEN, AMR M.
Applicants: APTIX CORP, APTIX CORPORATION
Application year: 1991
Main classification: H01L23
IPC codes: H01L21, G01R31, H05K1, H01L23, G11C29