Method of making a composite laminate and a PWB substrate so mad

Details Method of making a composite laminate and a PWB substrate so mad Method of making a composite laminate and a PWB substrate so mad

1996-07-25

1999-02-23

Krass, Frederick

Stock material or miscellaneous articles

Structurally defined web or sheet

Including grain, strips, or filamentary elements in...

428107, 428113, 428114, 428137, 428195, 428209, 428360, 428408, 4284735, 428901, 361748, 361751, 361792, 156166, 156169, 156174, 156176, 156233, 156269, 1562733, 1563077, 156324, B32B 900

Patent

active

058741526

DESCRIPTION:

BRIEF SUMMARY
The invention is in the field of printed wire board laminates and pertains to a method of making such a laminate comprising the steps of providing unidirectionally oriented parallel fibres (UD filaments) with a matrix material to form a composite UD layer and laminating a plurality of UD layers to form a UD crossply laminate. The invention also pertains to the resulting UD crossply PWB laminate.


BACKGROUND OF THE INVENTION

The term UD crossply laminate is used to indicate composite laminates of the known type with a plurality of layers of unidirectionally oriented parallel fibres (UD filaments) contained in a resin matrix, the UD filaments being arranged in different layers of crossing orientational directions, said layers being symmetrically positioned vis-a-vis a plane of symmetry through the centre of the laminate which runs parallel to its outer surfaces.
UD crossply laminates possess considerable advantages such as an improved surface quality, a comparatively low linear thermal coefficient of expansion (TCE) in the x and y directions, the option of incorporating a high content of fibres, and a favourable dimensional stability. In these respects UD crossply laminates are pre-eminently suitable as PWB substrate.
Such UD crossply PWB laminates are known from, int.al., U.S. Pat. No. 5,037,691 (Medney). The disclosed PWBs are manufactured by winding filaments about a square flat mandrel in several layers crossing at an angle of 90.degree., with the filaments being provided with curable matrix material by means of injection and/or impregnation. The matrix, which in consequence contains crosswise-applied layers of UD filaments, is then cured.
Other manufacturing methods in accordance with the above opening paragraph have been described in U.S. Pat. No. 4,814,945 (Leibowitz), EP 478 051, and WO 92/22191.
Leibowitz's disclosure relates to a PWB laminate comprising a matrix resin reinforced with parallel aramid fibres. The laminate is built up from layers of unidirectional aramid tape applied one on top of the other in crosswise fashion. The aramid tape is made by arranging a single layer of parallel aramid fibres to form fibre strips, coating the fibre strips with resin, and heating them to a semi-cured or "B"-stage.
EP 478 051 discloses the continuous manufacture of a flat substrate from a fibre-reinforced matrix, which process comprises the use of at least two moving layers of parallel, rectilinearly extending reinforcing fibres not bonded in the form of a woven fabric (UD fibres), providing said UD fibres, which are positioned in at least two crossing directions, with matrix material, and passing them through a laminating zone, for instance a double belt press, to form a crossply laminate.
In WO 92/22191 method of manufacturing a PWB laminate is described involving the steps of making non-flowable UD layers, coating at least part of the non-flowable UD layers with an adhesive on one or both sides, crosswise stacking the UD-layers in such a way that there is at least one layer of adhesive between each pair of UD-layers having a different direction of orientation, and bonding the stacked UD-laminates by activating the adhesive layers.
A general problem in the manufacture of UD crossply PWB laminates has to do with the step of providing the UD filaments with matrix resin. In order to fully benefit from the advantages of UD crossply laminates, the UD filaments should be orderly distributed over each UD layer. Problems may arise if portions of the filaments are not coated with matrix resin or if large resin areas are devoid of reinforcement. These problems include the occurrence of sink marks (highly undesirable surface unflatnesses due to differences in thermal expansion of portions of the laminate having different fibre volume fractions) and, in the case of PWBs made by additive plating, the occurrence of short circuits due to voids having become plated. This calls for an improved impregnation technique.
Another problem that particularly applies to the manufacture of UD-crossply laminates is that of disorie

REFERENCES:
patent: 4814945 (1989-03-01), Leibowitz
patent: 4943334 (1990-07-01), Medney et al.
patent: 4980217 (1990-12-01), Grundfest et al.
patent: 5037691 (1991-08-01), Medney et al.
patent: 5330595 (1994-07-01), Held
patent: 5496613 (1996-03-01), Middelman et al.
Int'l Search Report in PCT/EP95/00273 dated Jun. 2, 1995.
Chemical Abstracts 114:25517, "Polymer-Fiber Composites as Dielectrics and Their Manufacture", Sep. 1990.

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