Enhance Miniature Construction with Optical Feedback


Many microwave construction projects, and most modern equipment, use extremely small surface-mount components. Working with these parts requires steady hands and good vision. And as we get older, our vision usually deteriorates -- I got my first bifocals last year.

Iím convinced that the key to working with tiny parts is to see them well. When I built the first noise source with the tiny "0402" size ( 1 x 0.5 mm) chip resistors, it was frustrating trying to get the resistors soldered where I wanted them. After that experience, I was on the lookout for a surplus stereo microscope, and finally located one at a reasonable price. These microscopes are commonly used for microelectronics assembly work, providing moderate magnification at a long working distance.

After I set up the microscope on my workbench with adequate illumination, I was ready to build some more noise sources. Now the tiny chip resistors were clearly visible, and I was able to hold them in place with tweezers while soldering them exactly where I wanted them. On another project, I wanted a clearance hole in the ground plane around a hole drilled though a TeflonTM PC board. The hole is 0.025 inches in diameter, and I was able to cut an octagon around it with an X-ActoTM knife; the length of each side of the octagon is about the same as the hole diameter. Then I lifted the unwanted copper with the point of the knife. Magnification makes miniature work feel precise and easy instead of clumsy and frustrating.

What the microscope does is add gain to the feedback loop from the eyes to the hand. Our hands are never perfectly steady, but adding this feedback steadies them under the microscope, as the brain takes input from the eyes and automatically compensates (after a bit of practice).

A microscope is an elegant solution for very small parts, but any optical magnification helps. I have also used magnifiers, jewelers loupes, and "drugstore" reading glasses. If the reading glasses are stronger than you need, they will provide additional magnification; just donít try walking around wearing them.

Other aids to miniature work are tweezers, fine-point soldering irons, and lots of light. When an object is magnified, proportionally more light is required for the same apparent brightness. Tweezers help in holding small objects -- I prefer the curved #7 style Swiss tweezers, of stainless steel so solder wonít stick. Finally, a temperature-controlled soldering iron prevents overheating, which can destroy the solder pads on surface-mount components; 700° F tips are hot enough. All the tools Iíve mentioned came from hamfests, surplus places, or flea markets, at reasonable prices.

So, even if you think that microwave project with tiny parts is beyond your capability, use a magnifier and give it a try. Iíll bet you surprise yourself.

N1BWT


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