Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – For fault location
Reexamination Certificate
1998-07-16
2001-06-05
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
For fault location
C324S531000
Reexamination Certificate
active
06242923
ABSTRACT:
FIELD OF THE INVENTION
This invention is related to the testing and inspection of multi-chip modules or printed circuit boards and, more particularly, to a method of locating shorts between voltage planes or between I/O nets and power planes for purposes of diagnostics and repair.
BACKGROUND OF THE INVENTION
Power plane-to-power plane shorts are a common defect that typically necessitate scrapping an electrical component if they are not detected and repaired during the early stages of manufacturing. Locating shorts poses several significant yield and diagnostic problems. Firstly, shorts between power planes in an electronic package such as an MCM-D (multi-chip module provided with thin film layers) or a PCB (printed circuit board) are a generic and perennial problem both for yield and diagnostic considerations. Typically, an ohmmeter is used to determine the presence of power plane-to-power plane defects. However, to precisely locate the short is usually a formidable task, since such a defect can appear anywhere in the active area between adjoining power planes. Additionally, the complex nature of thin-film packaging makes it prohibitively expensive to inspect the entire MCM-D or PCB in order to determine the precise location of a short with a reasonable degree of accuracy. It is, therefore, highly desirable to have a method to pinpoint the location of power plane-to-power plane shorts in the most effective manner possible.
A second problem involves reliability considerations. Certain defects may be exceedingly tenuous, such as filamentary shorts which, typically, blow out when traversed by an even minimal current. For diagnostic considerations, it would be desirable to have a method for locating these fine shorts without destroying them, to gain valuable diagnostic information and helpful hints for an improved manufacturing process. Attempting to view such shorts with infrared techniques most likely will blow the short. Accordingly, as in the previous case, it is highly desirable to subject the short to minimal current stress while attempting to locate the short.
A third problem occurs in some shorts having a high resistance, and oftentimes, a significant amount of power plane-to-power plane capacitance. A method which can locate high resistance shorts in the presence of high power plane-to-power plane capacitance would therefore be highly beneficial.
A fourth problem, involves a specific defect known to be fatal: I/O net-to-power plane shorts. These defects oftentimes occur in an MCM-D on the highly dense TSM (Top Side Metallurgy, i.e., the side of the substrate to which chips are attached) that also involves a BSM (Bottom Side Metallurgy, i.e., the surface of the substrate to which pins are attached I/O nets). Repair opportunities for such nets are typically limited. In the presence of many levels of thin-films, shorts in this category frequently involve a power plane (rather than the more complex case of shorts between I/O nets). Moreover, both, electrical test and automated optical inspection techniques tend to be expensive. Thus, a simple, cost effective method of detecting and locating critical I/O net-to-power plane shorts is likewise highly desirable.
In summary, there is a need in the art of manufacturing MCMs and PCBs for an inspection technique which provides a sensitive and non-invasive approach to locating plane-to-plane defects. These include power plane-to-power plane shorts or any other types of plane-to-plane shorts, as opposed to linear trace applications. Typical linear trace applications include: tracing lines on a PCB; tracing a cable; open testing; and test and inspection of x/y lines on flat panel display applications such as LCD (liquid crystal displays). Practitioners in the art have in the past used pickup coils to locate such defects, mainly in the following applications: linear tracing of cables for shorts within the cable, linear tracing of lines on a PCB, and shorts between x,y lines on panel displays all while driving an oscillating current through the defect. The magnetic Faraday induction approach to be described in this invention is specifically directed towards plane-to-plane shorts and I/O nets-to-power plane shorts.
TSM metal patterns are extremely dense and expensive to make. In such instances, it may be simpler to detect a short with an ohmmeter if the pads on the BSM are provided with contacts to the power planes. Although detecting this type of defect may appear simple, locating the actual defect may be a formidable task since hundreds of thousands of places in the TSM may exist where two power planes or a power plane to an I/O net can short to each other. If two ground shielding planes are built parallel and in close proximity to one another, interlevel shorts can occur anywhere in the plane. It may be difficult and ineffective to rely on unassisted manual inspection of the entire area. It is, therefore, desirable to have an effective area scan method to locate this narrow class of yield detracting defects.
In U.S. patent application Ser. No. 08/807,076, plane-to-plane shorts are localized by an apparatus that includes: a current source; a means for applying current to the plane-to-plane short; an inductive magnetic field sensing probe for sensing changes in the magnetic field around the short; and circuitry for detecting a signal induced in the magnetic field sensing probe, when the probe is in the vicinity of the defect. This approach may subject the fragile electrical component to high current stresses and may lack adequate sensitivity for the more difficult case of finding high resistance power plane-to-power plane shorts.
Other related patents describe various electromagnetic probes to scan electronics packages in a variety of ways, although none address plane-to-plane shorts. The patents listed hereinafter can be divided into several groups according to their respective application: linear current trace probes with probes used as field sensors (electromagnetic); contactless techniques involving electrical testing using radiated electromagnetic signatures, wherein the probe is a field emitter and possibly also a sensor. None of these applications, however, address the special problems and concerns of power plane-to-power plane shorts or high resistance power plane-to-power shorts. Nor do they address the simplified case of I/O net-to-power plane shorts. Nor do they separate signals caused by noise or unwanted capacitive effects from the signal due to a power short.
Techniques for using electromagnetic sensor probes for scanning electronics packages are described in U.S. Pat. No. 5,406,209 to Johnson et al; U.S. Pat. No. 5,714,888 to Naujoks; U.S. Pat. No. 5,218,294 to Soiferman; U.S. Pat. No. 3,992,663 to Seddick; U.S. Pat. No. 4,186,338 to Fitchenbaum; U.S. Pat. No. 5,073,754 to Henley; and U.S. Pat. No. 4,542,333 to Koontz. All of the above utilize a magnetic field sensing probe as opposed to an electromagnetic field generating probe. These patents can be further classified into various groups highlighting different methods, as will be discussed below.
Johnson's U.S. Pat. No. 5,406,209; Naujoks′ U.S. Pat. No. 5,714,888 and Soiferman's U.S. Pat. No. 5,218,294 describe an array of broad spectrum electromagnetic sensing probes to scan a module undergoing a functional test in a go
o-go test. In the case of a power plane-to-power plane short, an ohmmeter is presumed to have already detected the presence of a short. In all the methods described above, an electromagnetic signature which was previously generated, is compared to a predetermined signature. A decision is made whether the PCB is good or bad. Generally, all the radiated electromagnetic energies sensed with the predetermined signature of the profile are compared, although the electromagnetic sensed energy is not necessarily helpful in locating a power plane-to-power plane short. A signal which strongly pinpoints the position of a voltage plane short is generated by a magnetic field. In contradistinction, an electrostatic field tends to be a degrading compon
Halperin Arnold
Scaman Michael E.
Yarmchuk Edward J.
International Business Machines - Corporation
Kerveros James C
Metjahic Safet
Schurmann H. Daniel
LandOfFree
Method for detecting power plane-to-power plane shorts and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for detecting power plane-to-power plane shorts and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for detecting power plane-to-power plane shorts and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2459798