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Nondestructive Measurement and Inspection Process

IP.com Disclosure Number: IPCOM000085623D
Original Publication Date: 1976-May-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

LaClair, GH: AUTHOR

Abstract

Present techniques for determining the amount of solder fill, etc. in plated through-holes (PTH) and the like of printed-circuit boards become more and more difficult, especially with the advent of very densely packaged products where the PTH diameter is small compared to its depth. Visual inspection can only confirm whether the outer ends of the PTH are filled. There can be substantial internal voids in the through-hole which would never be so detected by visual inspection.

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Nondestructive Measurement and Inspection Process

Present techniques for determining the amount of solder fill, etc. in plated through-holes (PTH) and the like of printed-circuit boards become more and more difficult, especially with the advent of very densely packaged products where the PTH diameter is small compared to its depth. Visual inspection can only confirm whether the outer ends of the PTH are filled. There can be substantial internal voids in the through-hole which would never be so detected by visual inspection.

The difficulty with these and other inspection techniques are overcome through the use of an X-ray exposure process, where the printed-circuit board is first oriented on a bias angle with respect to the X-ray beam, and is then rotated through a predetermined angle, prior to the taking of the X-ray exposure. The bias angle assures that the X-ray exposure will be taken over the entire length of the PTH, and the rotation angle assures that one hole area will not be blocked on the exposure by adjacent hole areas.

After the exposure is developed, it is viewed on a screen with suitable magnification to permit measurement and inspection of the entire area. For example, the developed film can be viewed on a microfilm viewer at 30X magnification, measured and inspected. This process allows the clear viewing of even miniature internal defects for easy detection.

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