microwave circuit board handle exposure to UV radiation
When it comes to manufacturing electronic devices, precision and reliability are paramount. As such, manufacturers must use innovative solutions that offer a range of benefits to streamline production processes across various sectors including printed circuit boards (PCBs), touchscreen displays and optical media. Ultraviolet light technology offers a wide variety of advantages that enhance the bonding process in these applications and more, improving performance while reducing cost.
The present invention relates to an apparatus for treating photoresist compositions on a substrate in the manufacture of microwave circuit board. The photoresist compositions are overlaid with a piece of artwork or mask, which prevents the penetration of UV radiation to certain areas of the substrate. For positive photoresists, the mask covers that which is to remain on the board; for negative photoresists, it covers that which is to be eliminated from the board. The resulting substrate is vacuumed between a print frame that contains windows of glass, Mylar or plastic and is treated with radiation from one or more electrodeless UV lamps. The lamp(s) can be provided with reflector means in a variety of configurations, to orient the radiation toward the photoresist.
A spray developer in a 1.5 percent NaOH solution is used to develop the exposed panels. The dosage of the panel is determined by comparing its clear value to the Stouffer Step Tablet (“SST”), a 21-step gray scale that will produce results that can be compared to the same results obtained with different developers and radiometers. The thickness of the coating is also taken into account, as a thicker coating will require a greater dosage of UV than a thinner coating.
How do microwave circuit board handle exposure to UV radiation?
Because the etching of copper-clad laminates involves a relatively high amount of energy, the choice of a dielectric material is important in the production of circuit boards. The material’s dielectric constant and loss tangent must be adequate, but not too low, in order to avoid distortion of the signals transmitted on the board.
It is important to note that the loss tangent of the material increases with increasing frequency, and this fact must be taken into consideration when selecting a suitable dielectric material for a circuit board. The material chosen must also be able to handle high voltage electrical discharges creeping over the surface of the board.
Conformal coatings are typically inspected using UV-A illumination, as the conformal coating is colorless and cannot be viewed under white light. To assist in this inspection, UV dyes containing fluorescing agents are added to the clear coating and the fluorescent properties are observed under a UV light source. The blue glow of the coating under UV illumination indicates the presence of trapped air bubbles and holes in the coating. Dark areas that don’t emit a blue glow indicate the absence of conformal coating. For example, circles with a glowing outer ring and a dark center are indicative of trapped air bubbles or pockets in the coating. The occurrence of these defects can be corrected by re-immersing the board in the conformal coating bath.