Just a small addition to the list below. It is rare that the spectral sensitivity of the radiometer photocell matches perfectly with the spectral sensitivity of the LPI. The numbers provided by the manufacturers are biased on the photocell they used in their lab and usually based on a mercury lamp spectrum. In recent years metal halide additive lamps have become the predominant lamp in the industry due to their efficiency, intensity, versatility, and lamp life. Now there are a variety of spectrums available. The spectrum of the lamp affects the: * exposure speed * resolution * surface tackiness * depth of cure Control of the production involves a combination of, millijoule readings for short term machine confirmation and calibration, gray scales to ensure cure, and resolution targets to ensure consistent performance in the event that a lamp would change spectrum toward the end of it's life. Bert Ohlig OLEC Corp. [log in to unmask] ---------- From: [log in to unmask] Sent: Wednesday, January 15, 1997 12:15 PM To: [log in to unmask] Subject: Re: Photo-initiation There are many, many types of photoinitiators used in the liquid, photoimageable (LPI) solder masks on the market. Some are faster and some are slower. Some respond to 365 nanometers, others at higher wave lengths, others at lower wave lengths. On and on. Putting a millijoule requirement (for example, 300 mj) for LPI solder masks can be very dangerous because there are so many factors that effect the correct exposure, such as: 1. The thickness of the solder mask deposit. Thicker deposits require more energy than thinner ones. 2. The wattage of the exposure unit. Higher wattage units (> 7 KW) will expose at lower millijoules than lower wattage ones (<3 KW). 3. The amount of heat buildup during exposure. Higher heat buildup will expose faster than low heat buildup. However, a high heat buildup can cause problems of artwork growth, sticking of the phototool, etc. 4. The d-min of the phototool used. Lower d-min will expose faster than higher d-min. >From my perspective, it is much better to use some type of step wedge (the Stouffer 21 step sensitivity guide is the most common one here in the USA) to determine the correct amount of exposure rather than an absolute energy level. Most of the LPI masks that I am familiar with provide the best all around performance (good sidewalls, good resolution, etc) with step wedge readings of clear metal 10-12. Good luck and don't hesitate to contact me if I can be of further assistance Larry Fisher Dexter Electronic Materials [log in to unmask] *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * *************************************************************************** *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************