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Producing Printed Circuit Boards

IP.com Disclosure Number: IPCOM000090531D
Original Publication Date: 1969-May-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 55K

Publishing Venue

IBM

Related People

Greene, KF: AUTHOR

Abstract

A multilayer printed circuit board 10, as in drawing I, is fabricated from a plurality of discrete board layers 12, 14, 16, and 18. Each layer is fabricated as shown in drawings A...H. Initially, thin copper foil 20 has applied to its undersurface positive photoresist layer 22 having a thickness of approximately 3-5 mils. Holes 24 are formed in photoresist layer 22 by exposing and developing the photoresist in areas where future through-holes are desired.

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Producing Printed Circuit Boards

A multilayer printed circuit board 10, as in drawing I, is fabricated from a plurality of discrete board layers 12, 14, 16, and 18. Each layer is fabricated as shown in drawings A...H. Initially, thin copper foil 20 has applied to its undersurface positive photoresist layer 22 having a thickness of approximately 3- 5 mils. Holes 24 are formed in photoresist layer 22 by exposing and developing the photoresist in areas where future through-holes are desired.

In drawing B, thin layers of gold 26 and copper 28 are sequentially electroplated onto foil 20 in the area of a hole 24. At this time, as in C, layer 22 is reexposed and developed to form future conductor lines 30 and future via holes
32. Additional layers of gold and copper 34 and 36 are electroplated into holes 24 and 32 and conductor line 30 as in D. Layer 22 is then striped off the plated foil 20 leaving the partially completed layer shown in E. At this time, the partially completed structure is turned over and the voids are filled in with an insulating material such as an epoxy-glass fiber mix 40 shown in F.

After the insulating material is cured to form layer 40, the surface of through- hole land 42 is ground until the copper is exposed. After land 42 is exposed, a tin-lead layer 44 is electroplated on it as in G. Then, with electrical contact being made to layer 20, adhesive coating 46 is electrostatically sprayed over the face of the insulation. The adhesive adheres only to layer 40 and not to the face of layer 44. The adh...