Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2000-04-26
2003-03-18
Sherry, Michael (Department: 2829)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S1540PB, C324S765010
Reexamination Certificate
active
06535005
ABSTRACT:
BACKGROUND OF THE INVENTION
A typical circuit board assembly process involves creating a circuit board and populating the circuit board with a variety of circuit board modules. In general, a circuit board manufacturer combines layers of non-conductive material (e.g., fiberglass or plastic) and conductive material (e.g., copper) into a rigid sheet. The manufacturer then mounts modules, i.e., circuit board components such as integrated circuits (ICs), capacitors, resistors, connectors, etc., onto installation locations (part attachment fields) of the circuit board in order to form a circuit board assembly. Finally, the manufacturer tests (and perhaps programs) the circuit board assembly to verify proper operation prior to releasing the circuit board assembly for commercial use.
On occasion, a manufacturer may determine that a particular portion of a circuit board assembly (e.g., a particular module installation location, an etch or trace location, a component, etc.) is a cause of improper circuit board assembly operation. In some situations, the cause is excess solder or debris on the surface of the circuit board (e.g., solder flux remnants and impurities). For example, a particular mounting process that mounts a lead frame IC package to a particular installation location of a circuit board can use a particular solder that leaves a large amount of solder flux residue on the surface of the circuit board. Such residue can lower the surface insulation resistance (SIR) of the circuit board causing a large amount of leakage current to flow between solder joints of the circuit board assembly. Often, the manufacturer can visually detect the residue and remove it (e.g., by washing the circuit board with a special cleaning solution or bath, by blowing air under and around the lead frame package, etc.). Furthermore, the manufacturer can visually inspect other circuit board assemblies to determine whether such residue is common to the circuit board assembly process or an isolated incident. If the residue is common to the circuit board assembly process, the manufacturer can modify the process to remedy the situation. For example, the manufacturer can reduce the residue by improving a cleaning procedure performed on the circuit board assemblies after the mounting process, or by changing the type of solder or flux used during the mounting process.
Some circuit board manufacturers perform stress tests on a sample of circuit board assemblies to determine how the circuit board assemblies will behave after an extended period of real-world use. That is, the manufacturers put the sample of the circuit board assemblies through a variety of environmental stresses (e.g., high temperatures, high humidity, high or prolonged vibration, etc.) which attempt to duplicate extreme real-world operating conditions, and/or accelerate aging of the circuit board assemblies. The manufacturer interprets the results of such tests as an indicator of the suitability of the circuit board assembly process and hopes that such tests will reveal circuit board assembly anomalies that could surface after a period of use. For example, the manufacturer may determine that a circuit board assembly process is unsuitable because solder joints formed during the module mounting process tend to weaken and break over time. The manufacturer can then improve the circuit board assembly process in order to avoid such anomalies in the future (e.g., by changing the temperature applied during the soldering process, by changing the type of solder used, by changing the dimensions or tolerances of pins and/or vias forming the solder joints, etc.).
Some circuit board manufacturers form test boards for testing particular attributes of a circuit board assembly process. One such test involves validating continuity between a test board and a special module which is mounted to the test board using a new circuit board assembly process. In this test, a manufacturer creates a test board, and solders the special module to a designated test board location in order to form a single conductive pathway through all of the solder joints holding the module to the test board. That is, conductive material within the module and within the test board connects the solder joints to form a single daisy chained pathway. After completion of the assembly process, the manufacturer verifies that the module and the test board properly form the single low-resistance pathway (i.e., verify continuity from one end of the pathway to the other), and subsequently subject the test board to a series of stresses that age the test board. Then, the manufacturer tests continuity between the module and the test board (i.e., repeat the continuity test) in order to determine whether the assembly process adequately mounted the module to the test board (i.e., in order to confirm that the assembly process mounts the module to the test board sufficiently to withstand the stresses).
Another test involves a manufacturer forming a comb structure on a test board using a particular circuit board assembly process. The comb structure generally mimics line width and spacing patterns to be implemented on particular circuit boards for commercial use. Such a comb structure includes conductive material on a surface of the test board. The conductive material forms an open pattern of straight, laterally-extending etch runs which can receive a first voltage (e.g., V
SS
of 10 to 100 volts) and a second voltage (e.g., V
GND
of 0 volts) in an interleaved manner. A manufacturer then applies the first and second voltages to the comb structure, and measures leakage current between the etch runs. In an optimal situation, the resistance is expected to be high, e.g., on the order of 10
6
to 10
8
ohms per square centimeter. In this configuration, cells formed between a first voltage etch and a second voltage etch provide straight voltage gradient lines which extend longitudinally between the laterally-extending etch runs (i.e., perpendicularly to the laterally-extending etch runs). The manufacturer then determines the surface insulation resistance (SIR) for the area of the comb structure by dividing the voltage difference (e.g., 10 volts) by the measured leakage current. This SIR is an indicator of the circuit board which the manufacturer can routinely expect when manufacturing commercial circuit boards having similar line width and spacing patterns. Typically, circuit board assembly processes that provide low SIRs are more susceptible to signal integrity anomalies, i.e., damage to the circuit boards from current leakage over a long-term can tend to weaken insulation properties between particular etches or traces resulting in circuit board assembly failures after a period of normal operation.
Occasionally, if there is surface area available, a circuit board manufacturer may place such a comb structure in a coupon on a commercial circuit board away from any mounted parts. This enables the circuit board manufacturer to obtain SIR information on the actual commercial circuit board. The Institution for Interconnecting and Packaging Electronic Circuits (IPC) of Northbrook, Ill. and other electronic trade organizations provide other test patterns and procedures for assessing the quality of circuit board assembly processes.
SUMMARY OF THE INVENTION
A circuit board may properly pass initial tests and inspections prior to its release by a circuit board manufacturer only to fail after a period of time (e.g., a year) of normal operation. The circuit board manufacturer may be able to isolate the cause of the failure to a particular module or module installation location. Occasionally, the circuit board manufacturer may be able to identify the exact cause of the failure. For example, if the module has a lead frame package, the manufacturer may be able to visually inspect the solder joints connecting the module to the circuit board and determine whether any debris or contaminants have caused a large amount of leakage current to flow between two solder joints. If such is the case, the manufacturer may be able to modify the circu
Chapin & Huang , L.L.C.
EMC Corporation
Huang, Esq. David E.
Nguyen Jimmy
Sherry Michael
LandOfFree
Systems and methods for obtaining an electrical... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Systems and methods for obtaining an electrical..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Systems and methods for obtaining an electrical... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3035823