The disclosures herein relate generally to testing electronic equipment and more particularly to a manufacturing test process that utilizes a readable signature of the frequency spectrum measured from the output of the AC power line.
Printed circuit boards (PCB) and printed circuit board assemblies (PCBA) require testing after the components have been affixed on the printed circuit board to determine interconnectional continuity, board functionality, and placement and connection of components. Several different approaches have been developed for testing PCBA's including, for example, functional testing, in-circuit testing, and continuity testing.
A common in-circuit testing technique to individually test each of the components on a printed circuit board is a "bed-of-nails" technique. The bed-of-nails technique uses fixed position spring-loaded probes to establish an electrical contact between test points on a PCB and the test equipment. The fixed-position spring-loaded pins (the "nails") are supported within a frame (the "bed") and connected to the test equipment via individual cables. Each particular bed-of-nails fixture is specially designed and manufactured with an appropriate number of pins suitably positioned to perform specific tests on a particular type of PCB. The design and manufacture of such fixtures is well established in the art. In general, when the board is first placed in the test fixture, it is not in contact with the test probes.
A known approach for bringing the printed circuit board into contact with the test probes is a vacuum assist method. The vacuum assist method forces connections between the PCB circuitry and the circuitry of the tester bed-of-nails by creating a vacuum between the PCB and the test probes. The vacuum provides the large amount of force necessary to overcome the spring pressures of a hundred or more individual probes.
Most commercially available test fixtures use a partial vacuum induced in the space between the board and the test bed to bring the board into contact with the probes. To achieve this, a flexible airtight seal is provided around the board. The seal is generally provided by a rubber seal with a spring means of returning the board to the upper position when the vacuum is released.
Although the vacuum assist method is effective in holding the PCB's in place, exclusive use of the vacuum assist method may cause undesired board flex. Excessive board flex is especially likely if the test probes are not evenly distributed about the total printed circuit board area. Board flex and subsequent associated failures can increase to a point of creating long-term reliability problems as a result of using vacuum pull down methods.
Thus, there is a trend to use mechanical hold-down fixtures to increase throughput and reliability of the bed-of-nails fixture. A mechanical hold-down fixture uses a hold-down gate, which includes a framework which is hinged and attached to a bed-of-nails fixture. The mechanical hold-down fixture pivots for inserting the PCB into and removing the PCB from the test fixture. The mechanical hold-down gate includes a plurality of parallel, sturdy bars. Hold-down fingers are located in channels within the bars.
Functional Testing is also sometimes implemented using a hot mock-up (HMU) technique. This method of test oftentimes uses a system-level testing platform with most common subassemblies connected together in order to assist in the determination of the unit under test (UUT) functionality. As an example, in the isolated case of a personal computer (PC) system, the main electronic logic assembly would commonly be connected manually to cables which connect to peripheral devices such as power supply, floppy disk, hard disk, memory modules, CPU modules, video monitor, keyboard, mouse, etc. Once the required hardware was completely connected, the mock-up would be powered on, diagnostics would be executed and the testing would usually result in a "pass" or "fail" status.
Functional testing can sometimes also be conducted using the bed-of-nails approach. Depending upon the development effort involved, this method can allow for a similar test to the HMU, but with improved throughput capabilities.
In both cases, HMU and bed-of-nails functional testing, a disk operating system (DOS) is read into memory and executed. Disk based diagnostics are usually then executed and after some amount of time and possible manual interactions with the diagnostics programs, a result of "Pass" or "Fail" is determined, (after which the HMU setup must be manually disassembled).
The amount of time spent in functional testing can range from only 3 or 4 minutes upward to hours or days depending upon the UUT intended end-use environment. In the case of the main logic assembly of a PC mentioned previously, the time for a HMU test may take 10 to 12 minutes on average depending upon the diagnostics executed and manual labor involved. The same functional test time for a bed-of-nails version of the same HMU test will usually average 6 minutes.
The amount of functional test time is extensive in a high volume production environment, both at the PCB manufacturing level and at the system level of assembly. This test time equates to a dollar expenditure in capital overhead and any reduction of test time with the same or better functional test coverage will equate with better Return On Invested Capital and overall profitability.