RU2462011C1 - Manufacturing method of multi-layer printed-circuit boards - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention can be used at manufacture of multi-layer printed-circuit boards (MPB) used during design of radio electronic equipment. MPB are obtained by bonding of two-sided and one-sided printed-circuit boards along flat surface through separating dielectric layers from glass fabric saturated with organic bonding agents; at that, electrical diagrams are not available on external surface of bonded boards. Then, through and blind bypass openings are drilled and metal wire with low electric resistance, for example copper, aluminium, or molybdenum, or silver one the diameter of which exceeds the diameter of bypass opening not more than by 5%, is inserted throughout the depth of the latter; after that, on external surface of bonded printed-circuit boards there applied subsequently is thin metal coating, by means of thermodecomposition of metal organic compounds (MOC) of nickel or copper, or cobalt, or molybdenum with thickness of 1.5-3 mcm; polymer organic substance in the form of film, and then, using photolithography or laser beam, or by milling there created is pattern of electrical diagrams, after which electroplated copper coating of required thickness is applied to the sections not protected with polymer film and protective metal resistive coating above it and residues of polymer and thin metal coating is removed.

EFFECT: simpler process for obtaining of multi-layer printed-circuit boards not containing any moisture, installation of electric contact between layers, which does not destruct at temperature drop; reduction of wastes of chemical electroplated manufacture.

Description

The invention relates to the field of electronics and can be used in the manufacture of multilayer printed circuit boards (MPP) used in the design of electronic equipment.

A known method of manufacturing MPP [1], which consists in the manufacture of single-sided or double-sided printed circuit boards on fiberglass, gluing them on the surface through a dielectric separating layer of fiberglass and organic binder during pressing, followed by drilling vias, their chemical and galvanic metallization.

Similarly, MPP can be obtained by the method [2], selected as a prototype. The main disadvantage of this method is that the metallization of the surface of the fiberglass and vias pass in aqueous solutions. In this case, the fiberglass is saturated with moisture and salts through the inner surface of the vias, especially when defects (seizures, cracks, etc.) occur on their inner surface. In this case, water, its vapors, salt solutions cannot be removed from fiberglass after metallization even with prolonged heating. Moving inside the fiberglass, they cause the closure of vias. Moreover, the higher the class of printed circuit boards, i.e. the closer these holes are in tight installation, the higher the likelihood of a short circuit. It was experimentally established that the adhesion of chemical copper to fiberglass does not exceed 10 kg / mm ² , which is insufficient, therefore, it is possible to peel the metal coating from fiberglass with a temperature difference.

Great difficulties arise when metallizing through vias with a diameter of less than 500 microns, as well as "deaf".

It was found that when drilling vias in the fiberglass MPP, the binder is wrapped in layers on the copper ends, resulting in the absence of electrical connection between the MPP layers after metallization.

The disadvantage of the prototype is the use of expensive palladium chloride as an activator for the deposition of chemical copper.

The objective of the invention is to remedy the above disadvantages and obtain MPP, not containing moisture, having good electrical contact between the layers, not violated by a temperature difference.

The specified technical result is achieved by the fact that in the method of manufacturing multilayer printed circuit boards (MPP), including the manufacture of single-sided and double-sided printed circuit boards, gluing them on a flat surface through separating dielectric layers of fiberglass impregnated with an organic binder, and there are no electrical circuits on the outer surface of the glued boards , drilling through and blind vias, insert a metal wire with low electrical resistance to the entire depth of the latter, for example copper, or aluminum, or molybdenum, or silver, whose diameter exceeds the diameter of the vias by no more than 5%, after which a thin metal coating is successively applied to the outer surface of the glued printed circuit boards by the thermal decomposition of organometallic compounds (MOS) of nickel or copper, or cobalt or molybdenum with a thickness of 1.5-3 microns, an organic polymer in the form of a film, and then by means of photolithography or a laser beam, or by milling create a drawing of electrical circuits, after which unprotected the polymer film plots the plated copper coating of the required thickness, and on top of it a metal-protective coating and remove the remnants of the polymer and thin metal coating.

The method is as follows: in any known manner produce single-sided and double-sided printed circuit boards. Then they are glued together on a flat surface through a separating dielectric layer of fiberglass impregnated with a binder. There are no electrical circuits on the outer surface of the glued printed circuit boards. Drill through and “blind” vias, insert a wire with low electrical resistance, such as copper or aluminum, or molybdenum, or silver, the diameter of which exceeds the diameter of the vias by no more than 5%. The obtained MPP billet is placed in a vacuum chamber in which a thin electrically conductive metal coating with a thickness of 1.5-3 microns is obtained by thermal decomposition of the MOS of nickel, or copper, or molybdenum, or cobalt on the surface of the lower, upper, and lateral. After metallization, a polymer film is glued onto the flat metallized surface of the upper and lower boards, and drawings of electrically conductive circuits are created by laser beam or photolithography, or by milling. Plots of the required thickness are coated with a galvanic copper coating of the required thickness, and a metal-resistive coating is applied over it, the remaining polymer coating is removed and a thin metal sublayer of nickel or cobalt, or copper, or molybdenum is etched and a multilayer printed circuit board is obtained.

It was experimentally established that if the diameter of the wire exceeds the diameter of vias by more than 5%, microcracks occur in the fiberglass.

If the diameter of the wire is smaller or corresponds to the diameter of vias, there is a lack of electrical contact between the layers, especially when temperature changes.

Using infrared (IR) spectroscopy, it was found that MPPs do not contain moisture.

The adhesion of the metal coating to fiberglass is 200 kg / mm ² .

LITERATURE

1. OST 107.460092.028-92.

2. GOST 23770-78 "Printed circuit boards. Typical technical processes of chemical and galvanic metallization "(prototype).

Claims (1)

A method of manufacturing multilayer printed circuit boards (MPP), including the manufacture of single-sided and double-sided printed circuit boards, gluing them on a flat surface through dividing dielectric layers of fiberglass impregnated with an organic binder, and there are no electrical circuits on the outer surface of the glued boards, drilling through and blind vias, characterized in that to the entire depth of the latter insert a metal wire with low electrical resistance, for example copper, or aluminum, or mol bdenic, or silver, the diameter of which exceeds the diameter of the vias by no more than 5%, after which a thin metal coating is successively applied to the outer surface of the glued printed circuit boards by thermal decomposition of organometallic compounds (MOS) of nickel or copper, or cobalt, or molybdenum with a thickness of 1 , 5-3 microns, polymer organic in the form of a film, and then by the method of photolithography or a laser beam, or by milling, they create a pattern of electrical circuits, after which they are applied to unprotected polymer film a galvanic copper coating of the required thickness, and on top of it a metal-protective coating and remove the remnants of the polymer and thin metal coating.