FR2485865A1 - LAMINATE FOR PRINTED CIRCUIT BOARD AND METHOD OF MANUFACTURING THE SAME - Google Patents

Abstract

LAMINATE WITH A COEFFICIENT OF THERMAL EXPANSION ALLOWING THE USE OF DISCRETE COMPONENTS WITHOUT CONDUCTIVE WIRES. IT INCLUDES: SEVERAL FLAT LAYERS, IN SURFACE-TO-SURFACE CONTACT, AND LINKED TO ONE ANOTHER TO FORM A COMPOSITE LAMINATE STRUCTURE, IN WHICH AT LEAST ONE OF THE LAYERS 28 IS FORMED OF DIELECTRIC MATERIAL, AND AT LEAST ONE OTHER OF THE LAYERS IS A STABILIZING LAYER 24 SHAPED FROM A METAL HAVING A COEFFICIENT OF THERMAL EXPANSION LOWER THAN THAT OF THE DIELECTRIC LAYER, WHICH ALLOWS THE STABILIZING LAYER TO ADJUST THE COEFFICIENT OF THERMAL EXPANSION APPLICABLE TO THE STRUCTURE 10. APPLICATION OF THE STRUCTURE.

Description

1

  The present invention relates to a laminate for

  multilayer printed circuit board which includes

  one or more stabilizing metal foils intended

  to reduce the coefficient of thermal expansion of the laminate. In addition, a new two-step manufacturing process has been discovered which makes it possible to arrange openings in the stabilizing metal layer and prevents air from being trapped in these openings when they are filled with resin. epoxy. In the prior art, laminates have been used for

  printed circuit boards for mounting and connecting

  inexpensive electrical components.

  We equip more particularly circuit boards

  formed of a dielectric substrate of metallic tracks

  conductors that establish electrical connections between discrete components mounted on this substrate. It is possible to weld the metallic conductors of the components to the tracks

  conductors to perfect the electrical connections.

  The dielectric substrate used to form the

  The printed circuit board is generally made of a fiberglass fabric which has been impregnated with a resin composition and for example epoxy resin or polyimide. The thermal expansion coefficient of the dielectric substrate is much higher than that of the discrete components. The difference in thermal expansion coefficients has not constituted a major disadvantage since the flexibility of the metallic conductors of the discrete components compensates for the difference in thermal expansion. Even in cases where the

  circuits is subject to variations or excur-

  frequent and intense thermal

  cant can compensate for the difference in thermal expansion in

  designing a circuit layout that places expansion loops

  in the conductors of the components to absorb the di-

  dilations and withdrawals of the elements and thus avoid

  constraints on the weld seams which are the main cause

blade breaking circuit.

  Recently manufacturers have designed components

  deprived of conducting wires, like resistances in pastil-

  the capacitors or pellets. When the pelletized components without lead wires, generally formed of alumina, are attached directly to a circuit board or conductive layer of a multilayer laminate,

  discovered that the difference in thermal expansion coefficients

  between the dielectric substrate and the components in step

  alumina cells without lead wires resulted in

  very many breaks in the circuit. The coefficient of dilatation

  The thermal density of a conventional dielectric substrate consisting of an epoxy-glass resin laminate is more particularly of the order of 15 to 20 × 10 -6 cm per cm 2 per degree Celsius. On the contrary, the alumina pellet components have a much lower coefficient of thermal expansion, generally about 6.10-6 cm per cm per degree Celsius. So when a laminate for circuit board carrying components

  conductors is subject to thermal excursions.

  important factors, the solder joints between the components

  and the strafified yield frequently as the flexibility allows

  to compensate for the differences in dilation between

  posers and the laminate no longer exists. It therefore appeared

  It is desirable to make a circuit board laminate that has a closer coefficient of thermal expansion.

  the coefficient of thermal expansion of the components in pastil-

  alumina to prevent breakage of electrical connections.

  In addition, it would be desirable to provide a circuit board laminate which is further constituted by substrates

  of glass-epoxy resin since these substrates have advantages

  considerable economic benefits and are relatively easy to

manufacture.

  In accordance with the above, we realize a new

  metal laminate for improved circuit board

  which has a coefficient of thermal expansion

  reduced, especially suitable for use in connection

  sound with components devoid of conductive wires. In particular, a circuit board laminate comprising a plurality of flat layers adhesively bonded to a laminate structure by bonding layers formed of epoxy resin impregnated glass fabric is described. In a preferred embodiment, the printed circuit board laminate of the present invention comprises an upper conductive planar metal layer formed of a copper foil and a stabilizing layer formed of a metal having a coefficient of thermal expansion less than the coefficient of thermal expansion that would present the composite strafified structure alone. We put a layer for circuit board

  printed as is done in conventional

  multiple layers below the stabilizing metal layer.

  A lower layer is placed below the layer for

  printed circuit board. Conductive metal layers

  are designed to receive

  alumina components without lead wires. Leaves

  the bonds formed of resin-impregnated glass fabric are interposed between the layers. In accordance with the production method of the present invention, a structure is formed

  partial composite by assembling the metal layer separately

  upper planar conductor and the stable metallic layer

  lisatrice. The partial composite structure and the remaining layers are then assembled to form a complete composite laminate. This unique two-stage laminate manufacturing process ensures the filling of the through holes formed in the stabilizing layer with resin which prevents air

  to be trapped, as will be described more fully below.

  The resulting printed circuit board laminate

  a very low coefficient of thermal expansion, this

  which allows the laminate to be used with components that

seen from conducting wires.

  In another embodiment of the present invention, the

  stabilizing layer is formed of a composite metal composite

  dielectric allowing it to present a trace of the type not

contiguous, floating.

  The remainder of the description refers to the appended figures

  1, an exploded view of the components of the multi-layer circuit board laminate corresponding to a first embodiment of the present invention; Figure 2 is a partial sectional view of the partial composite laminate structure obtained after the first step of the new improved manufacturing method of the present invention;

  FIG. 3 is a partial view of the laminate for

  multi-layer circuit board terminated on which are mounted conventional components and components devoid of conducting wires; -. FIG. 4 is an exploded view, similar to that of FIG. 1, showing a second embodiment of the multi-layer circuit board of the present invention, in which a structure is used for the stabilizing layer.

  composite metal-dielectric material allowing it to present

a non-contiguous line.

  Referring to FIG. 1, a view is shown

  burst of laminate for multi-layer circuit board

  The laminate comprises an upper layer 20 of conductive metal material, preferably formed from a sheet of paper.

  copper approximately 0.051 mm thick. -

  Under the metal layer 20 several

  connecting sheets 22 formed of a conventional material for

  multi-layered quilts as a fiberglass fabric

  impregnated with resin. The bonding sheets 22 serve as adhesion

  sif and electrical insulating dielectric material between the metal layer 20 and the stabilizing metal layer 24 placed below. The choice of the metal of the stabilizing layer

  24, which has a coefficient of thermal expansion lower than

  than that of the dielectric layers depends on the coefficient

  desired thermal expansion for the final composite laminate.

  Before forming the laminate, the stabilizing layer 24 is profiled and large openings 26 are made to ensure clearance for the final stages of the manufacturing process when

  pierces the through-connection holes and metallises them.

  In a preferred embodiment of the present invention, the stabilizer layer 24 is covered with copper so that it can be used as a grounding plate or a firing plate.

  voltage, in addition to its main stabilization function.

  We can treat the upper and lower surfaces of the

  stabilizing layer 24 with copper oxide to enhance

  improve adhesion to the bonding sheets placed above and below. A conventional printed circuit board 28 is placed under the stabilizing layer 24 by interposing a second bonding layer 30. The printed circuit board is

  classical model, with multiple layers and is preferably

  of a glass fabric impregnated with an epoxy resin or

  mide. The circuit board carries several electrical tracks-

  conductive elements 31 which connect the components. It is necessary to

  take that although a layer for

  28, the invention covers any multilayer laminate structure in which,

  for example, the tracks of the circuits would have been

  as for the upper and / or lower metal layers 20 and 32, a lower conductive metal layer 32 is placed by interposing a third bonding layer 34 between the layer

  lower conductor 32 and the printed circuit board 28.

  Second and third bonding layers 30 and 34 similar

  the bonding layers 22 are formed of unprotected glass fabric

  epoxy resin. The lower conductive layer 32

  to the upper conductive layer 20, is preferably

  made of 0.051 mm thick copper foil; The upper surface of the conductive layer 20 can be pretreated with copper oxide to improve adhesion. Both

  upper and lower conductive layers 20 and 32 are suitable

  for use in connection with aluminum components

  mine without wires 34, as well as with the

  conventional components 36, as shown in FIG.

  In accordance with the present invention, there is disclosed a

  The invention provides a novel process for producing the multi-layer circuit board of the present invention. More particularly, it is not possible to directly adapt the methods of the prior art for the manufacture of multi-layered wafers to the present invention, since the present invention comprises

  a stabilizing metal layer 24 pierced with large openings

  26 which must be completely filled with epoxy

  during the process of forming the laminate. In addition, the

  must prevent air from being trapped in the openings.

  A new manufacturing process has therefore been developed.

  two stages in which the metal layer is heated first.

  The upper layer 20 and the stabilizing metal layer 24 are bonded together to form a partial laminate structure, after which the remaining layers are combined and heated.

  to produce a complete stratified structure. More specifically

  firstly, in the first laminate forming step, one or more bonding layers 22 formed of resin-impregnated glass fabrics are interposed between the upper metal layer 20 and the stabilizing metal layer 24.

  a relatively large amount of epoxy resin to replace

  completely close all the openings in the metal plate

  than. A partial laminate structure is then formed with the metal and stabilizer layers 20, 22 and 24 so that the resin of the bonding layers 22 fills the apertures 26. This distinct initial laminate-forming step allows the resin of free flow in the openings 26 without air being trapped, as one

represented it in figure 2.

  In the second stage of formation of the struc-

  completed, the remaining layers and the structure

  As is shown in FIG. 3, conventional laminates are used. Conventional methods are used to complete the fabrication such as drilling and metallization of the through holes which facilitates the formation of the electrical connections. We can then attack the metal layers 20, 22 and place pins for components without conductors

  in accordance with the conventional platelet manufacturing process.

multi-layer circuit.

  The multilayer circuit board laminate tests of the present invention as

  shown in FIGS. 1-3, including staggered metal layers

  bilisatrices between 0.127 and 0.381 mm have

  resulted in an average thermal expansion coefficient of

  Viron 8.9.10 t cm per cm per degree Celsius over a range of -55 to 1250C. Multi-layer circuit board laminates on which lead-free pellets carriers were mounted, withstand more than 400 cycles

  of thermal stresses by Mil Std 202 (these

  cooked at thermal cycles between -55 and 1250C) without

  that they present rupture in 2000 points of welding.

  Referring to FIG. 4, there is shown a second embodiment of the present invention, which in the same manner as for the first embodiment, comprises a plurality of layers that can be assembled to form a multi-layer circuit board. metal soul that presents a

  coefficient of thermal expansion set. The circuit board

  cooked 110 comprises, more particularly upper layers

  and lower 120 and 132, consisting of cooking sheets

  about 0.051 mm thick. A circuit pad layer 128 formed of a dielectric substrate can be placed

  electrically conductive tracks.

  placed several bonding layers 122, 124 and 134 between the other layers, as dielectric, and to provide the resin

  epoxy necessary to maintain the layered structure.

  In the second embodiment of the present invention, there is disclosed a composite stabilizing layer 140 which has a lower coefficient of thermal expansion. Layer

  stabilizer 140 is more particularly composed of a

  central dielectric tracing 142 and two outer metal layers 144 and 146, assembled to form a composite structure. The dielectric substrate layer 142 may be made of glass fabric impregnated with resin, while the layers

  144 and 146 each having a thickness of the

  0.076 to 0.254 mm are chosen depending on the desired expansion coefficient for the final circuit board laminate. The stabilizing layer 140 of the second embodiment

  of the present invention, has certain advantages over

  to a stabilizing layer consisting of a metal core

  unique. More specifically and as shown

  FIG. 4, the configuration of the trace formed in the metal core

  that 144 need not necessarily be contiguous with the

  that constitutes the soul since the whole soul is suppor-

  by a dielectric substrate. In other words, the stabilizing layer 140 may have on its soul a "floating-type" pattern which may comprise, for example, parts 148 which are not contiguous with the rest of the core 144.- The stabilizing composite layer 140 presents still the advantage during the laminate forming process of allowing easier filling of the relatively large open portions of the layers with the resin. The danger of air being trapped in

  the open parts 150 is therefore significantly reduced, which means that

  to form the laminate in one step. As in the

  first embodiment of the present invention, it is possible to

  the stabilizing layer 140 of an electroconductive metal, allowing the layer to serve as a ground plate or

under pressure.

  In summary, a new laminate for a plate is made

  multi-layer circuit circuit having a coef-

  The reduced thermal expansion factor is particularly useful in connection with components without lead wires, and a method is developed to manufacture it. We describe more

  particularly a laminate for a circuit board having

  multiple layers, to which one or more stabilizing metal layers have been incorporated. The circuit board laminate includes lower and upper layers that can accept lead-free components. A conventional printed circuit board layer and one or more stabilizing layers are sandwiched between the metal layers.

  formed of a metal having a coefficient of thermal expansion

  low. Several bonding sheets, made of resin-impregnated glass fabric, are interposed between all the layers

  previous, as an adhesive. In the new manufacturing process

  First, a laminate is formed with the metal layer.

  and that the stabilizing metal layer so that the resin of the bonding sheets can flow freely into the openings - arranged in the stabilizing metal layer without air being trapped therein. A partial laminate structure is formed followed by a complete laminate structure by joining the remaining layers. This latter structure can be completed in accordance with conventional manufacturing processes. The present invention reduces the coefficient of thermal expansion of the wafer laminate

  circuit to be used in conjunction with

  alumina posers which also have a low coefficient of thermal expansion. In addition, the use of metal stabilizer plates creates excellent surface conditions for multilayer platelet laminates, and these plates can also be used as an earth plate or

power on.

Claims (12)

RESUME ICAT IONS   1. Laminate for metal core circuit board   characterized in that it comprises: a plurality of flat layers, in surface-to-surface contact, and bonded to one another for the purpose of being used with components having no conductive wires, to form a stratified structure   composite, wherein at least one of the layers (28) is   dielectric material, and at least one of the other   ches is a stabilizing layer (24) formed of a pre-   having a coefficient of thermal expansion less than that of the dielectric layer, which allows the stabilizing layer to adjust the coefficient of thermal expansion   of the composite laminate structure (10).   2. Laminate for multi-layer circuit board   ples according to claim 1, characterized in that the layer   stabilizer contains at least one through hole (26).   3. Laminate for multi-layer metal core circuit board according to claim 2, characterized in that it further comprises a bonding layer (22) placed against the stabilizing layer (24) and constituted by a sheet of glass fabric impregnated with resin to facilitate filling of the through-hole in the stabilizing layer during the laminate formation.   Laminate for multi-layer metal core circuit board according to claim 1, characterized in that the stabilizing layer (24) contains at least one hole through (26) filled with resin.   5. Laminate for multi-layer metal core circuit board according to claim 1, characterized in that   that the hole is lined with an electroconductive material.   Laminate for multi-layered metal core circuit board according to claim 1, characterized in that the stabilizing layer (24) is covered with copper.   which allows it to serve as a power-on plate.   Laminate for multi-layer metal core circuit board according to claim 1, characterized in that   that the opposite surfaces of the stabilizing layer have been   trice (24) with copper oxide to improve adhesion adjacent layers.   8. laminate for multi-layer metal core circuit board according to claim 1, characterized in that the stabilizing layer (110) is formed of a composite laminate structure comprising a central dielectric layer   (142) and two outer metal layers (144,146).   9. laminate for multi-layered metal core circuit board according to claim 8, characterized in that the outer metal layers (144,146) of the composite stabilizing layer (140) have a floating-non-contiguous pattern. 10. Laminate for multi-layered metal core circuit board having a coefficient of thermal expansion set for use with components without lead wires, characterized in that it comprises: a planar upper conductive metal layer (120);   A planar stabilizing layer (140) formed of a metal having a low coefficient of thermal expansion; a planar printed circuit board layer formed of a dielectric substrate (128); a lower flat conductive metal layer   (132), the upper and lower conductive metal layers   may accept components without conductor wires.   tors; and three planar bonding layers (122,124,134) formed of an epoxy resin impregnated fabric, one of the bonding layers (122) being interposed between the upper conductive metal layer (120) and the stabilizing layer (140) and contiguous   to these, a second tie layer (124) being   placed between the stabilizing layer (140) and the printed circuit board layer (128) and contiguous thereto, and the third bonding layer (134) being interposed between the   printed circuit board layer (128) and the metal layer   lower (132), and adjacent thereto, the bonding layers adhesively bonding the other layers to form a composite laminate structure in which the   stabilizer layer adjusts the coefficient of thermal expansion of the stratified structure.   A method of manufacturing a multilayered metal core circuit board laminate having a controlled coefficient of thermal expansion for use with lead-free components, comprising: providing an upper planar conductive metal layer (120) and a stabilizing layer (140) formed of a metal having a low coefficient of thermal expansion; interposing a bonding layer (122) between the conductive metal layer and the stabilizing layer, the bonding layer being formed of resin impregnated glass fabric; forming a partial composite laminate structure with these layers;   20. the provision of a printed circuit board layer   me (128) and a lower flat metal layer (132); interposing a second bonding layer (134) between the printed circuit board layer and the lower metal layer and interposing a third layer   connection (128) between the lower surface of the static layer   bilisatrice and the upper surface of the printed circuit board layer; the second and third tie layers being formed of glass cloth impregnated with resin; and the formation of a composite laminate structure complete with these layers.