May, 2018
www.us-tech.com
Page 77
The question is complicated, since the requirements of the application, work environment and sample are the primary considerations. Also,
What’s Next for Visual and Optical Inspection? I
By Mark Clymer and Ed Balcerzak, UNITRON, Ltd., and Kieran Slicker, Ash Technologies, Ltd.
t is difficult to decide which sys- tem is best for inspecting and ensuring circuit board integrity.
tance of 8 in. (20.3 cm), and the work- ing distance of an 11-diopter shrinks to 3.75 in. (9.5 cm), which is barely enough room to safely place a board under the magnifier.
Inspection Lighting Good lighting goes far beyond
having some overhead lights in the shop. Shadows can lead to poor assembly production, higher rejec- tion rates and missed flaws during inspection. Magnifiers can be pur-
chased with integrated illumination, but supplementary illumination or task lighting often enhance the oper- ator’s performance. The type of illumination should
be a consideration. While incandes- cent or halogen lighting were the original gold standards, fluorescent lighting became the norm for decades. Now, new LED sources offer attractive options for task lighting. However, LED illumination is not all the same. Some LED lights appear
more blue or “colder” and some appear more yellow or “warmer.” Halogen and incandescent light
intensity can be readily increased or decreased as needed, but the appear- ance of the light changes with the voltage, giving a whiter light at its brightest, and more yellow light as it is dimmed. On the other hand, LEDs maintain their color cast across the intensity range. It is best to try the different types of illumination to
Continued on next page
LUXO Microscopes by UNITRON System 273 Greenough-stereo design microscope with ring light.
where a traditional inspection sys- tem may have been sufficient in the past, advances in manufacturing technology are dictating the need for more sophisticated instruments.
Conventional Magnifiers Magnifiers were the first tools
to aid in the assembly and inspection of circuit boards. Not much more advanced than a magnifying lens on an arm, these instruments have a simple lens and are a logical choice where a low level of magnification is needed to perform soldering and to observe and inspect solder joints and other features on the sample. If the sample can be seen satisfactorily through a magnifier, is more magni- fication necessarily better? Magnifiers are available with
fixed magnification rated in diopters. Diopter roughly translates to power or the magnification factor of the magnifier, where a higher diopter rating equals higher magnification.
When the components or details of the sample get smaller, the solution is to buy magnifiers with higher diopters, right? Not so fast.
A simple calculation can be used to determine the magnification power a magnifier: simply divide the diopter factor by 4, then add 1. For example, a 3-diopter lens on a magnifier gives a magnification power of 3/4 + 1 = 1.75x. A 4-diopter has a magnifica- tion power of 2x, and a 5-diopter has a magnification power of 2.25x. When the components or details
of the sample get smaller, the solu- tion is to buy magnifiers with higher diopters, right? Not so fast. Diopters also have a relationship to working distance. The working distance is the optimal distance a magnifier needs to be from the sample for best view- ing — this is similar to focal length. So, the higher the diopter, the short- er the working distance and the clos- er the magnifier needs to be to the sample. A 3-diopter has a working distance of 13 in. (33 cm) — plenty of room for hands and tools. By con- trast, a 5-diopter has a working dis-
See at SMT Hybrid Pkg., Booth 4A-536
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