LASER SOLDERING BASIC INFORMATION AND TUTORIALS

Two types of laser have been applied to solder reflow—carbon dioxide (CO2) and neodymium-doped yttrium-aluminum-garnet (Nd:YAG). Both generate radiation in the infrared region with wavelengths of about 10.6 μm from the CO2 laser and 1.06 μm for the YAG laser.

The wavelength of 1.06 μm is more effectively absorbed by metal than by ceramics and plastics; the wavelength of 10.6 μm is normally reflected by conductive surfaces (metals) and absorbed by organics.

The main attributes of laser soldering are short-duration heating and highintensity radiation, which can be focused onto a spot as small as 0.002 in (0.050 mm) in diameter. With these inherent attributes, laser reflow is expected to

■ Provide highly localized heat to prevent damage to heat-sensitive components and to prevent cracking of plastic IC packages

■ Provide highly localized heat to serve as the second or third reflow tool for assemblies demanding multiple-step reflow

■ Require short reflow time

■ Minimize intermetallic compound formation

■ Minimize leaching problems

■ Generate fine-grain structure of solder

■ Reduce stress buildup in solder joint

■ Minimize undesirable voids in solder joint

With these attributes in mind, laser soldering is particularly beneficial to soldering densely packed regions, where local solder joints can be made without affecting the adjacent parts, to soldering surface mount devices on printed-circuit boards having heat sinks or heat pipes, and to soldering multilayer boards.

In addition, it also provides sequential flexibility of soldering different components and enhances the high-temperature performance of adhesives used for mounting surface-mount devices.

With respect to reflow time, laser soldering can be accomplished in less than 1 sec, normally in the range of 10 to 800 ms. The laser can be applied to pointto- point connections through pulsation as well as to line-to-line connections via continuous laser beam scan.

The fine-pitch flat-pack devices have been connected to printed wiring boards using YAG continuous laser beam scans on each side of the package.

Both the use of prebumped solder pads and the direct application of solder paste are feasible. In directly reflowing solder paste, although using spattering and heat absorption problems have been observed, they are not incurable.

To eliminate these problems, the preheating and predrying step is necessary. Location of laser beam impringement is another factor. In addition, compatible properties of solder paste have be designed to accommodate fast heating in relation to fluxing and paste consistency, coupled with the proper design of the equipment and its settings.

LASER CONTROLLED ON OFF SWITCH USING 555 TIMER BASIC ELECTRONICS PROJECT

HOW TO MAKE LASER CONTROLLED ON OFF SWITCH?

This is a basic electronic project on how to make a laser controlled on/ off switch using a 555 timer. Below is its schematic diagram.

This circuit is built around a 555 timer using very few components. Since the circuit is very simple, even a novice can easily build it and use it as a controlling device.

A laser pointer, now easily available in the market, can be used to operate this device. This circuit has been tested in operational conditions from a distance of 500 metres and was found to work satisfactorily though it can be controlled from still longer distances.

 Aiming (aligning) the laser beam exactly on to the LDR is a practical problem. The circuit is very useful in switching on/off a fan at night without getting off the bed. It can also be used for controlling a variety of other devices like radio or music system.

The limitation is that the circuit is operational only in dark or dull-lit environments. By focussing the laser beam on LDR1 the connected gadget can be activated through the relay, whereas by focussing laser beam on LDR2 we can switch off the gadget.

The timer is configured to operate in bistable mode.

LASER DIODES BASIC AND TUTORIALS

LASER DIODES BASIC INFORMATION
What Are Laser Diodes?

The laser diode is a further development upon the regular light-emitting diode, or LED. The term "laser" itself is actually an acronym, despite the fact it's often written in lower-case letters.

"Laser" stands for Light Amplification by Stimulated Emission of Radiation, and refers to another strange quantum process whereby characteristic light emitted by electrons transitioning from high-level to low-level energy states in a material stimulate other electrons in a substance to make similar "jumps," the result being a synchronized output of light from the material.


This synchronization extends to the actual phase of the emitted light, so that all light waves emitted from a "lasing" material are not just the same frequency (color), but also the same phase as each other, so that they reinforce one another and are able to travel in a very tightly-confined, nondispersing beam.

This is why laser light stays so remarkably focused over long distances: each and every light wave coming from the laser is in step with each other:

Incandescent lamps produce "white" (mixed-frequency, or mixed-color) light. Regular LEDs produce monochromatic light: same frequency (color), but different phases, resulting in similar beam dispersion.

 Laser LEDs produce coherent light : light that is both monochromatic (single-color) and monophasic (single phase), resulting in precise beam confinement.

Laser light finds wide application in the modern world: everything from surveying, where a straight and nondispersing light beam is very useful for precise sighting of measurement markers, to the reading and writing of optical disks, where only the narrowness of a focused laser beam is able to resolve the microscopic "pits" in the disk's surface comprising the binary 1's and 0's of digital information.

Some laser diodes require special high-power "pulsing" circuits to deliver large quantities of voltage and current in short bursts. Other laser diodes may be operated continuously at lower power.

In the latter case, laser action occurs only within a certain range of diode current, necessitating some form of current-regulator circuit. As laser diodes age, their power requirements may change (more current required for less output power), but it should be remembered that low-power laser diodes, like LEDs, are fairly long-lived devices, with typical service lives in the tens of thousands of hours.