Stock material or miscellaneous articles – Structurally defined web or sheet – Including grain – strips – or filamentary elements in...
Patent
1993-12-02
1996-03-05
Ryan, Patrick J.
Stock material or miscellaneous articles
Structurally defined web or sheet
Including grain, strips, or filamentary elements in...
428113, 428232, 428288, 428290, 428209, B32B 900
Patent
active
054966132
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a base material for printed wire boards (PWBs) in the form of a laminate adapted to be used as a supporting board for a printed circuit and comprising layers of an electrically non-conductive matrix material reinforced with unidirectionally (UD) oriented fibres. The invention , also pertains to a method of manufacturing same.
DESCRIPTION OF THE PRIOR ART
Such base materials follow from the disclosure of U.S. Pat. No. 4 943 334, in which PWB substrates are described that are manufactured by a process which comprises winding reinforcing filaments about a square flat mandrel to form several layers of filaments intersecting at an angle of 90.degree.. The materials so produced possess the advantage of having a low coefficient of expansion. A drawback that may occur is that of a relatively high interlaminar stresses due to the anisotropy of the reinforced layers. There is a danger of these stresses leading to delamination or to so-called transverse cracks being formed in the laminate. A further disadvantage resides in the high production costs.
A more simply producable laminate has been described in FR 1,229,208. This laminate comprises rigid composite layers alternating with adhesive layers. As the composite material cardboard impregnated with a phenolic resin is disclosed. The disclosed adhesive material is based on silicone rubber. The person of ordinary skill in the art will immediately appreciate that the laminate described is not in accordance with modern standards.
The current standard base materials for printed wire boards are generally manufactured according to the process described in, e.g., C. F. Coombs, Jr.'s Printed Circuits Handbook (McGraw-Hill), which includes the following steps:
Woven glass fibres are impregnated with a solution of epoxy resin in MEK.
Next, the solvent is evaporated and the resin partially cured up to a so-called B-stage.
The resulting prepreg is cut to length and stacked between two copper foils.
This package is cured under pressure at elevated temperature in a multidaylight press.
The laminate coated with copper on both sides manufactured in this manner is then formed into a printed wire board by etching.
Despite being the current standard, the material manufactured in this known manner displays several disadvantages, e.g.:
unequal and often too high thermal expansion in the laminate plane.
a high coefficient of expansion in the Z-direction.
high coarseness of the surface on account of the fabric structure.
high materials costs on account of the high costs of fabrics.
Moreover, the process is not environment friendly, since mostly harmful solvents, such as MEK and DMF, are employed. A further drawback to the process is the large number of generally labour-intensive process steps required.
It has been attempted to obviate the last-mentioned drawback by using a double belt press instead of multidaylight presses. Such a process is known, int. al., from EP-0215 392 B1. The advantages claimed for this known process are less product quality variation and lower production costs. Nevertheless, there are a number of drawbacks to this process also, such as unequal expansion in the X and Y directions and a low surface quality.
U.S. Pat. No. 4 587 161 discloses a production process for printed wire boards in which the substrate is composed of a mixture of epoxy resin and unsaturated polyester resin reinforced with glass fabrics or a randomly oriented glass fibre mat. Among the advantages attributed to this process are a lower cost price and a number of improved properties, including a lower dielectric constant. A drawback to this material, however, is that its thermal coefficient of expansion is significantly above the level presently desired by the electronics industry.
To meet the requirement of lower coefficients of expansion, substrates have been developed which are based on polymers with higher glass transition temperatures. In this way a reduction of the overall thermal expansion is attained over the temperature range from ro
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Printed Circuits Handbook, by C. F. Coombs, Jr., Chapters 31 (pp. 31.3 to 31.32), 32 (pp. 32.1-32.22), 33 (pp. 33.1 to 33.21), 34 (pp. 34.1 to 34.18) and Glossary (pp. 6.1 to 6.9).
Middelman Erik
Zuuring Pieter H.
AMP-Akzo LinLim VOF
Fennelly Richard P.
Lee Kam F.
Morris Louis A.
Ryan Patrick J.
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