Optics: measuring and testing – Inspection of flaws or impurities
Reexamination Certificate
2001-04-02
2003-02-25
Lee, John R. (Department: 2881)
Optics: measuring and testing
Inspection of flaws or impurities
C348S126000, C029S833000, C358S461000
Reexamination Certificate
active
06525811
ABSTRACT:
BACKGROUND OF THE INVENTION
Circuit boards typically include one or more circuit board components such as integrated circuits (ICs), resistors, capacitors, and connectors. Circuit board manufacturers often visually inspect the quality of solder joints which connect these components to the circuit boards. For example, a circuit board manufacturer may periodically examine a few circuit boards from a circuit board assembly line in order to verify that the circuit board components have been properly soldered to the circuit boards. As another example, a manufacturer may choose to rework a circuit board than scrap it. To this end, the manufacturer may unsolder an incorrect, defective or out-of-spec circuit board component from the circuit board, solder a new one in its place, and examine the resulting solder region prior to releasing the reworked circuit board from manufacturing.
Typically, a technician manually performs the inspection process. During inspection, the technician typically wishes to see a uniform and robust set of solder joints connecting each component in question to the circuit board. A healthy solder joint is generally characterized by a shiny, smooth and even appearance. Examples of poor soldering include solder joints that have a dull finish (indicative of cold solder joints), solder joints that have a granular appearance (indicative of inadequate heating), angled solder joints between mis-aligned or mis-registered solder pads, excessive voids between solder pads, and solder joints having solder shorts or “bridges” to neighboring pads.
There are a variety of conventional approaches to examining the solder region between a circuit board component and a circuit board. One approach (hereinafter referred to as the “handheld tool approach”) involves the use of a microscope and a handheld tool. The handheld tool is similar in shape to a dental mirror in that it includes a handle and a small mirroring portion (e.g., a polished section of sheet metal) fastened to an end of the handle. A technician holds the handle and manually maneuvers the mirroring portion around the edge of the component by moving the handle. The technician views the solder region between the component and the circuit board by tilting the handle in such a way that light reflects from that solder region off of the mirroring portion through the microscope. Accordingly, the technician can examine the periphery of the solder region to either confirm proper soldering of the periphery, or identify poor or unhealthy solder joints.
Another inspection approach (hereinafter referred to as the “rework station approach”) involves the use of a rework station for reworking circuit boards. A typical rework station includes a heating platform for heating the underside of a circuit board requiring rework, and an integrated positioning assembly for positioning and installing a component (e.g., an IC) onto the circuit board. The positioning assembly includes a prism assembly, a microscope, a nozzle, and a movable frame on which the prism assembly, the microscope and the nozzle are mounted. During component installation, a technician inserts the component into the nozzle, and moves the movable frame such that the nozzle and the component resides over the mounting location of the circuit board. Typically, the technician looks at the mounting location (which is typically printed with solder paste) through the microscope and the prism assembly while simultaneously operating geared knobs of the movable frame in order to precisely register the component over the mounting location. The technician then lowers the component onto the mounting location, and blows heated gas (e.g., nitrogen) over the mounting location through the nozzle in order to solder the component to the circuit board. After the technician has allowed the solder to cool, the technician can inspect the solder region by looking through the microscope and prism.
Another inspection approach (hereinafter referred to as the “computer camera” approach) involves the use of a specialized computer system having a miniature computer camera and a light source mounted to a movable frame, and a computer monitor that displays images gathered near the miniature computer camera. To inspect the solder region between a circuit board component and a circuit board, a technician operates the movable frame (i.e., moves geared knobs) to move the computer camera next to the solder region. The computer monitor then displays images of the solder region for inspection by the technician. The technician can store the image in the computer system (e.g., as a JPEG file) or, if the computer system further includes a printer, can print permanent pictures of the solder region for subsequent inspection of the solder region (e.g., for subsequent inspection by an engineer responsible for maintaining or improving the component mounting process).
It should be understood that a camera can also be used in the above-described handheld tool and rework station approaches. In particular, a camera can be mounted to the microscopes used in those approaches to take permanent pictures of soldering regions for subsequent review.
SUMMARY OF THE INVENTION
Unfortunately, there are deficiencies to the above-identified approaches to examining the solder region between a circuit board component and a circuit board. For example, if a camera is used in the conventional handheld tool approach, it is often difficult for the technician to take well-focused pictures of the solder region for subsequent review (e.g., by an engineer responsible for improving the soldering process). In particular, it is very difficult for the technician to hold the handheld tool steady so that an image of the soldering region properly reflects through the microscope while simultaneously looking through the microscope and operating the camera to take a picture. It is common for the technician to inadvertently move the handheld tool while taking the picture so that the picture is slightly out of focus thus losing details of the solder region. Accordingly, the engineer subsequently reviewing the picture will not be able to see particular features of the soldering region which were not captured by the picture. On the other hand, if a camera is unavailable, the technician would have to thoroughly document his or her findings (e.g., identify the particular corner, side or solder joint) so that the inspection process can be easily reproduced once the findings are brought to the attention of the engineer.
As another example, in the conventional rework station approach, rework station equipment is an expensive resource. If the same technician that reworks circuit boards is responsible for thoroughly inspecting the solder regions after the rework is complete, the throughput of that technician (i.e., the number of circuit boards that the technician can rework in a given period of time) can be substantially reduced and significantly increasing rework costs. Alternatively, if another technician performs the inspection process in order for the first technician to sustain maximum throughput, another rework station is needed for the other technician to perform the inspection process. The cost of rework stations can be $80K to $100K or even more depending on the sophistication of the equipment. As such, the equipment cost of the additional rework station may make the rework station approach too expensive to use for the inspection process.
As yet another example, in the conventional computer camera approach, the specialized computer system is also an expensive resource. The cost of such a system can be $30K or more. As such, the equipment cost of the specialized computer system may make the computer camera approach too expensive to use for the inspection process as well.
In contrast to the above-identified conventional inspection approaches, the invention is directed to techniques for inspecting a circuit board using an apparatus having a base that can rest on the surface of the circuit board, and reflective members for reflecting light from a circuit board c
Barr Gordon O.
Gray Bruce
Paladino James J.
Chapin & Huang , L.L.C.
EMC Corporation
Huang, Esq. David E.
Lee John R.
Vanore David A.
LandOfFree
Method and apparatus for inspecting a circuit board 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 and apparatus for inspecting a circuit board, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for inspecting a circuit board will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3160725