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www.us-tech.com
Choosing the Right Lighting for Machine Vision Applications
Continued from page 53
Structured lighting makes use of a known light pattern (normally a plane of light creating a line) which is used to gain dimensional information. In general, highly-collimated light sources are used, such as lasers or
For many years, machine vision has been a critical tool in PCB assembly. Solder validation would be difficult or impossible manually, due to the density of
components on the board.
fiber optic line lights. This technique is an inexpensive way to measure depth and height of continuous sur- faces. It is often used when either the light source or the surface are moving. Structured lighting can also show sur- face details on low-contrast parts.
Diffuse on-axis lighting (DOAL) allows light to be shined directly at an object in line with the camera without the light source ruining the camera’s image. This is accomplished by using a 50 percent silvered mirror to reflect light directly at a part. The camera then captures the image as reflected in the mirror. DOAL applications include detecting flaws on shiny, flat surfaces or inspecting the insides of small cavities.
The other diffuse technique is diffuse off-axis lighting, also known
as “cloudy day” lighting or “dome light” illumination. With this tech- nique, the light is not reflected direct- ly onto the part, but first onto a diffuse surface and bounced onto the part. The diffused off-axis method negates shadows —as if one were looking at an object on a cloudy day. It also avoids creating hot spots or glares, which cause problems in parts inspection.
Always-On or Strobed Lighting in machine vision appli-
cations is either always-on or strobed. By strobing a light, the image will gain increased intensity, and the light
camera shutter speed and the speed of the object need to be taken into account. Also, it is necessary to consid- er the effect of ambient light where the machine will be installed. The light used for inspection needs to be bright enough to overwhelm the ambient light surrounding the system. There are many lighting options
available, and many different ways to construct and orient the vision sys- tem for inspection applications. The surface of the object under inspection and its surroundings will dictate the type of lighting and the light’s posi- tion. This combination of light source
February, 2016
The Evolution of Cleaning Methods in PCB Rework
Continued from previous page
rework, and usually have to be scrapped if faulty. The problem stems from the fact that two different types of solder are used in manufacturing, with melting points of 183 and 302°C (361 and 575°F) respectively. Improp - er manual cleaning can change the melting temperature of the solder on the pads so the temperature may not be high enough to form a connection, resulting in a dry joint. In addition, many Package-on-
Package (PoP) chips cannot be confi- dently cleaned with manual methods due to the threat of melting the bot- tom package. A highly advanced component, the Invensas BVA PoP holds the solder balls on with fish- hook shaped connectors 50µ wide and 90µ high, barely visible to the unaided eye, and spaced at 0.2mm (0.008-in.) intervals.
Contact-Less Cleaning Contact-less cleaning — also
A dot matrix code viewed in ambient direct light.
source may last longer. More useful however, is the ability of a strobed light to make an object appear stopped. The timing of the strobe needs to be controlled precisely and coordinated with the camera, or the images will vary in intensity. The
A dot matrix code viewed with diffuse on-axis lighting (DOAL).
and where it is placed, will negate or accentuate features as appropriate. Contact: Cognex Corporation,
1 Vision Drive, Natick, MA 01760 % 877-264-6391 fax: 508-650-3344 E-mail:
pr@cognex.com Web:
www.cognex.com r
Los Angeles Office: 3528 Torrance Blvd., Suite 100
Torrance, CA 90503 Phone: (310) 540-7310 Fax: (310) 540-7930
Atlanta Office: 1580 Boggs Rd., #900
Duluth, GA, 30096 Phone: (770) 446-3116 Fax: (770) 446-3118
called scavenging — can alleviate the challenges associated with manual cleaning, and will supplant it entire- ly in many applications. For exam- ple, there is no contact made with the pad or board, reducing the risk of mechanical damage. Precision con- trolled tips can clean pads too small and too close together for human operators to reasonably attempt. The software and equipment continually
Continued on next page
San Francisco Office: 26230 Industrial Blvd.
Hayward, CA 94545 Phone (510) 293-0580 Fax (510) 293-0940
Patented, Next-Generation Soldering Technology
Main Features
•Outstanding reduction of voids
•Variety of models available including inline •Optimal tact time with patented conveyor transfer
by using vacuum zone •Energy-saving and with easy maintenance flux collection system Model: RSV12M-512-RLF Model: RSV12M-512-RLF Visit us at
www.seikausa.com to see more of our products!
EIGHTECH TECTRON CO., LTD.
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