Browse Prior Art Database

Expose Machine Shutter Control Unit

IP.com Disclosure Number: IPCOM000036574D
Original Publication Date: 1989-Oct-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 4 page(s) / 58K

Publishing Venue

IBM

Related People

Magyar, RJ: AUTHOR [+3]

Abstract

In the manufacture of printed circuit boards, an important process is one that involves the placement of the line channels on the panel in which copper will be deposited. This process involves the application of a light-sensitive polymer to the epoxy substrate. When the polymer is exposed to a specific wavelength of light, it undergoes crosslinking which makes it insoluble in methylchloroform. The unexposed areas on the panel, i.e., those areas covered by the pattern on the glass covering the panel during exposure, are dissolved out, leaving channels. (Image Omitted)

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 32% of the total text.

Page 1 of 4

Expose Machine Shutter Control Unit

In the manufacture of printed circuit boards, an important process is one that involves the placement of the line channels on the panel in which copper will be deposited. This process involves the application of a light-sensitive polymer to the epoxy substrate. When the polymer is exposed to a specific wavelength of light, it undergoes crosslinking which makes it insoluble in methylchloroform. The unexposed areas on the panel, i.e., those areas covered by the pattern on the glass covering the panel during exposure, are dissolved out, leaving channels.

(Image Omitted)

To maintain the quality of the exposed polymer, care must be taken to obtain the correct exposure time. The exposure time is determined by the cumulative energy reaching the panel surface and it varies depending upon the light intensity. Underexposed polymer will result in poor quality line channels after developing. On the other hand, overexposure can result in the brittling of the polymer. Brittling is a problem that affects the adhesion of the polymer to the panel. The adhesion is critical during the copper plating process to ensure line formation without shorting. Also, poor exposure, whether over or under exposure, can cause various other photoresist-related defects.

A traditional method of measuring the exposure energy is with a step wedge. The step wedge is actually a strip of photographic film with rectangular numbered blocks. The blocks are of different optical densities with step number 1 being the lowest density. When the step wedge is exposed over the polymer, the resulting pattern, which is read manually and is operator dependent, gives a direct indication of the energy received at the panel's surface. If the bulk intensity is assumed constant, then one simply measures the amount of time it takes to get the proper step wedge reading.

(Image Omitted)

However, since the bulk intensity changes over time, the exposure energy in that time frame also changes. This requires that a step wedge be exposed at regular intervals to correct the exposure time. Since all bulbs do not dim at the same rate, a probabilistic model for varying the exposure time over time will have to also incorporate the usage, individual machine power loads, and different vendor bulbs. It would be very difficult to come up with more than a rule-of- thumb procedure.

Adding a light energy detector, such as a luminometer, provides one way of tracking changing exposure times. Since the luminometer measures the amount of lumos reaching it, energy can be monitored by a display or gauge. The expose machine discussed has a luminometer set to 'trip' off the power when the correct energy is reached. That is, however, its only output function. There is no on-line monitoring capability.

The major drawback to the current set-up is that the determination of the exposure energy is a manual process. Because of this, human error influences the step wedge readings.

1

Page 2...