DE2209815A1 - Conductive object - Google Patents

Description

Dr. Ing.Walter Abitz
Or. Dieter F. Morf

Dr. Hans-A. Browns

March X, 1972 4

EGG. DU PONT DE NEMOURS AND COMPANY 10th and Market Streets, Wilmington, Delaware I9898, V.St.A,

Conductive object

The invention relates to laminated articles, in particular conductive laminates suitable as printed circuit boards.

U.S. Patent Application 779,602 filed Nov. 27, 1968 is a laminated item described, which is suitable for manufacture of boards for printed circuits, especially those manufactured at elevated temperatures and / or are used. Copper or Nieke foil bonded to the laminate has the disadvantage, however, of the increased Temperatures to form oxides; these oxides thus impair the adhesion of the usual solders if they are repeatedly different electronic elements are connected to the plate. It is therefore desirable to have a circuit board in which the metal foil bound to it does not oxidize and which the later operations in the production of printed Circuits not adversely affected or changed.

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The laminated article according to the invention has

a) an inner substrate which has at least one layer of fibrous sheet material, which with a polymeric precursor of a polyimide resin is impregnated, this resin being the reaction product of a Is anhydride component and an amine component,

b) a conductive metal bonded to at least a portion of at least one surface of the inner substrate is and

c) a substantially continuous nickel / boron alloy coating on the conductive metal part, the alloy having a boron content of about 0.1 to 15 percent by weight.

The inner substrate according to the invention has at least one Layer, preferably a plurality of layers, of sheet-like material with a polyimide resin, its precursors which are polyamide acids, polyamide esters and polyamide »acid amides, is impregnated. Various polyamic acid precursors are in U.S. Patents 3,179 6l ^ # 3,190,856, 3,179,635 and 3,182,073. Polyamide esters are described in US Pat. No. 3,312,663, and. one class of polyamic acid amides is known from US Pat. No. 3,260,691. Let it be on this Referenced patents.

Preferred polyimide precursor polymers are the polyamic acids described in US Pat. No. 3,179,614 the general formula

HO -

N
t

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where ^ is isomerism, R a tetravalent

represents an organic radical containing at least two carbon contains atoms, with no more than two carbonyl groups of each polyamic acid unit on any of the carbon atoms of the tetravalent radical are bonded ,, R 'a divalent Radical containing at least two carbon atoms, the amide groups of these adjacent polyamic acid units are each bonded to separate carbon atoms of the divalent radical, and η a whole The number is sufficient so that an inherent viscosity of at least 0.1, preferably from 0.3 to 5> 0, measured on a 0.5% strength by weight solution in N, N-dimethyl ~ acetamide at J0 ° C.

These polyamic acids are prepared by adding at least one organic diamine with at least one tetra carboxylic dianhydride using solvents and under conditions according to US Pat. No. 3,179,614. Special diamines and dianhydrides are also described there, but benzophenone tetracarboxylic acid dlanhydride and m-phenylenediamine are preferred.

Without being required, inert, thermally stable materials are preferably added to the polymeric precursor of the imide-containing polymer. Such materials are colloidal particles or particles of the following materials: carbon black, polyimide molded powder, as described in US Pat. No. 3,249,588, barium titanate, potassium titanate, magnesium sulfate, titanium dioxide, asbestos, magnetic iron oxide (Fe ^ O ₂ ,) , Iron (III)> »oxide (Fe 0,), aluminum powder, potassium« sodium tartrate, ammonium dihydrogen phosphate, amorphous aluminum oxide of the non-abrasive grain

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Type ("non-abrasive") and amorphous silicon dioxide of the non-abrasive grain type, such as glass microbubbles ("microballoons"), preferably barium titanate. The class of silicas of the non-abrasive grain type also includes the various forms of colloidal "Ludox" silicas, "Celite" kieselguhr (essentially SiO ₂ , plus AlpO, Fe ₂ O, TiO ₃ , CaO and MgO), "Synthamica "(a synthetic mica obtained using a stoichiometric ratio of SiOp, AlpO, MgO, potassium silicoflubride and potassium feldspar)," Hi-Sil "silicon dioxide (a hydrated silicon dioxide of high purity and very fine particle size), colloidal" Cab-0 ~ Sil "silica, and sepiolite (meerschaum, a hydrated magnesium silicates Some forms of aluminum oxide of the non-abrasive-grain type are boehmite, (a form of bauxite, Al ₂ OH ₂ O)," Celite "diatomaceous earth (see above) and" Bentone " 18 (complex magnesium / calcium / aluminum / silicon oxide, which is bound to an organic ammonium cation via electrovalence). Colloidal silicon dioxide has proven to be a particularly fragile material. These particles are by nature It has a spherical shape, a particle diameter below 0.1 Ju and a surface area of 200 to 200 m / g.

The content of inert, thermally stable, colloidal particles is usually at least about 0.5 # - based on the combined weight of the ahydride component and the amine component of the polymeric precursor; a salary above about 20 % on the other hand should not be worthwhile. Taking into account an imbalance of factors, including reducing the cavity

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tonnage, the higher thermal stability and increased preservation of the flexural strength at elevated temperatures * usually provide amounts ranging from 5 to 12% _t particularly preferably in the range of 5 to 10% ₃ satisfactory results.

The precursor can be mixed with the particles or the particles can be mixed with the precursor at any stage mix when making the prepress. For example, the particles can with the solution in the organic Solvent of one or both of the reactants mixed before, during or after the formation of the precursor be, or the particles can even before the introduction of the reactants of the precursor with the organic Solvents are mixed. The particles are preferably mixed with a solution of the precursor.,

Methods for mixing the polymeric precursor and colloidal particles include normal and hooh « speed stirring, sand milling, as in the USÄ patent documents 2 58I 414 and 2 855 I56 described, ball milling, Milling on a two-roll mill oclar other methods, such as they are used for the production of pigment dispersions » the.

For a resin impregnation are particularly suitable fibrous sheet materials at a temperature above 200 ° C, most preferably about 4Q0 ^o C, resistant sindj this includes the glass fabric no, Iö4, 108, 112 and II6, heavier glass fabric places, such as fabric no. I8I, glass fabric in which the yarn is not twisted and plied, like glass fabric No. 7721, flat fabric made from parallel glass fibers

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material, glass fibers, asbestos fibers and sheet material made from such and similar fibers and therefrom manufactured surface materials.

The fibrous material can be impregnated by any suitable method. For example may be the fibrous material with the precursor composition or the composition of the particulate material and the precursor are coated or immersed in such a composition.

The precursor often has such a viscosity that it is sticky or tough »which makes it difficult to store and handle the impregnated sheet materials. It is therefore often desirable to remove some of the solvent that may be present and, preferably, to partially cure the polyamic acid precursor, ie partially convert it into an imide-containing structure so that the sheet material is less tough or tacky. This solvent removal and conversion can be accomplished by the action of heat or by any of the other methods described in the patents referenced above. Usually such partially cured sheet materials are about 5 to 99.5 percent converted to a polyimide resin. The degree of conversion is preferably about 90 to 99.5% » Such partially cured sheet materials are particularly economical because they can be conveniently sold to further processors who then convert them into laminates.

The impregnated sheet materials can be laminated by any suitable method.

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Usually the simultaneous application of heat or some other agent to the precursor is done with which the fibrous sheet material is impregnated to completely convert into polyimide resin by pressure to to consolidate the individual sheet materials into a uniform laminate and, if desired, by vacuum, to remove volatiles that develop in the final conversion of the precursor to the polyimide resin. In the manufacture of the laminate, anyone can desired number of layers can be used, but in general the laminate preferably has a thickness of Range from 0.127 mm (for applications where flexibility is desired) to 6.35 mm (5-250 mils), Usually the thickness of the laminate is between 0.254 mm and 3.18 mm (10 to 125 mils), and usually it will be in the region of 1.52 to 1.78 mm (6o to 70 mils).

When making printed circuit boards from these laminates, a conductive metal is adhered to one To arrange part of at least one surface of the laminate (or the entire surface). Preformed metal sheets or sheets of the desired thickness, e.g., 0.0127 to 0.127 mm (0.5 to 5 mils), preferably from 0.0254 to 0.508 mm (1 to 2 mils), with or without Nickel / boron alloy pre-plating, are applied to an or bonded both surfaces of the laminate prepared as above. The material of the conductive metal foil can Be nickel, copper, silver, or any other conductive precious metal; Nickel or copper are preferred .

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To improve the solderability with the above-described laminated articles made of printed circuits a substantially continuous coating of a nickel / boron alloy is deposited on the conductive metal, which is about 0.1 to 15, preferably 0.1 to 2 wt.% Boron in the alloy, the coating thickness preferably being at least 0.0005 mm. The top thickness is not critical and is influenced by the cost and time to apply the coating; however, the thickness of the coating is usually in the range of 0.0005 to 0.127 mm (0.02 to 5 mils), preferably 0.00254 to 0.0254 mm (0.1 to 1 mil). A continuous nickel / boron alloy coating is a coating which, when magnified twenty times under the microscope, shows no interruption, ie does not show the underlying base metal in the field of view. At z. B. Copper as a sub-metal will not be detectable in a reddish color. The nickel / boron alloy coating has been characterized as a substantially continuous, as occurring in a non-significant area interruption does not affect the solderability.

The nickel / boron alloy coating is formed from an amine-borane-containing coating by electroless or non-electrical deposition Bath applied in accordance with U.S. Patent 3,358,726. The coatings can also be electroless using the borohydride bath according to US Pat. No. 5,096,182 be applied. Reference is made to these patents in this regard.

The following examples serve to further explain the invention; Part 'and percentages relate to calibration,

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unless otherwise stated, by weight.

Comparative example

A copper-plated and a nickel-plated circuit board made of glass fiber reinforced aromatic polyimide Both were tested for solderability after exposure to air at 200 to 450 ° C for 1 hour. the Both the copper and the nickel surface tarnished visibly above 200 ° C and were using a 6o / 4O ~ Zlnn ~ lead solder and a non-corrosive flux based on rosin (Dutch Boy 115) no longer solderable.

Metal" Flux Solderability after 1 200 300 350 Hour at ⁰ C 450 surface used 20th no 400 copper no Yes Yes no no no copper Yes »T no no nickel no dd Yes no no no nickel Yes If no

“Solderable” is to be understood as meaning that over 95 % of the surface was wetted by solder within 20 seconds in the solder area at a temperature of 215 ° C. This example highlights the inherent susceptibility of common copper and nickel to passivation at elevated temperatures.

example 1

The tests of the comparative example were repeated with the copper-plated circuit board after a 0.00254 mm (0.1 mil) thick nickel / boron coating

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(0.5 % boron, remainder nickel) according to USA patent J5 J>J> Q 726 had been applied to the copper foil.

Metal-

Flux solderability after 1 hour at C

Surface used 20 200] 5ÖÖ 350 4 * ÖÖ450

Nickel-Boron No Yes Yes No "Yes Yes Yes Yes Yes Yes No

The application of a nickel / boron coating on the copper surface thus extends their usability from 200 to over 400 ° C. This test came out with the same result repeated with nickel / boron on the nickel-plated circuit board.

Example 2

The tests of the comparative example were carried out with the copper-clad Circuit board repeated after a 0.00254 mm thick coating of nickel / boron (5 percent Boron, the remainder nickel and stabilizer) has been applied to the copper foil in accordance with US Pat. No. 3,096,182 was.

Metal flux Solderable after 1 hour at ⁰ C surface used 20 2ÖÖ jJÖÖ 2 | Ö 400 450 Nickel-Boron No Yes Yes No

"Yes Yes Yes Yes Yes No

As in Example 1, the presence of the nickel / boron coating increases the usefulness of the material from 200 above 350 ° C. This test was carried out with nickel / boron on the nickel-plated circuit board repeated with the same result.

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Example 3

In this example, the thickness of the nickel / boron coating was (0.5 percent boron, remainder nickel) on copper-clad circuit boards varies and the solderability according to 1 hour exposure to 400 ° C in air.

Thickness of the coating,

mm (Micro! Solderable Coverage, however pitted 0.05 x 3 no a few scar 0.508 3 > $ 90 1.27 x 3 * 99 & 2.54 · 3 $ 100 .nch) ■ 0 " ⁵ (2) ■ O " ⁵ (20) ■ 0 " ⁵ (50) .0 " ⁵ (100)

This example shows that the solderability with the Dioke of the nickel / boron coating increases.

Example 4

In this example, a 0.0381 mm (1.5 mil) thick copper foil was coated on both sides with 0.00254 mm (0.1 mil) nickel / boron (0.5% boron, balance nickel) as in Example 1 and then on a circuit board made of fiberglass-reinforced aromatic polyimide is laminated in the same conventional manner as in the amination of the copper foil. While the bond strength between the copper and the polyimide in a lift-off test using test squares of 3.175 mm (1/8 ") on a side, a wire being soldered to such a square and then tensile stressed to breakage, is about 4.5 When the tensile strength was 10 pounds, the nickel / boron bond with polyimide had a tensile strength of 25 pounds.

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Example 5

A nickel / boron coating (0.5 % boron, balance nickel) was applied as in Example 1 to a pattern formed by etching the copper of the copper-plated circuit board prior to the nickel / boron plating, the nickel / boron -Layer coated both the edges of the copper and the surface, which gave the composite bondability even after 250 hours in air at 2βθ ° C. The same pattern was then made by etching after applying the nickel / boron coating. A certain attack occurred with delamination at the nickel / copper interface. In contrast, when the same pattern was formed on a laminated plate with uncoated copper after this treatment, delamination occurred on the surface due to air oxidation at the substrate / copper interface.

Example 6

The copper-clad circuit board of Example 1 coated with nickel / boron (0.5 % boron, remainder nickel) could easily be soldered with a variety of solders and non-corrosive positive agents, for example with 6θ Sn / 40 Pb. 95 Sn / 5 Ag, 95 Sn / 5 Sb and 90 Pb / 10 Sn ("Formon" solders from EI du Pont de Nemours and Company).

Example 7

A nickel / boron coating (0.5 % boron, the remainder nickel) was applied to copper particles which were glued to a circuit board made of glass fiber reinforced aromatic polyimide. The conductivity of the composite material prior to the nickel / boron plating was 4.5 ohms per unit area.

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After plating with 0.00228 mm (0.09 mil) nickel / boron, the conductivity was 0.01 ohms per square improved. The metal surface was now easily solderable while using it before coating itself corrosive plus materials could not be soldered.

A special, preferred embodiment of the invention is directed to the fact that the conductive metal is prefabricated nickel or copper foil adhesively bonded to the base, the nickel / boron alloy at least; on the outer surface of the film is present Lind a thickness of at least 0.0005 mm, said most preferably the nickel / boron alloy has a boron content in the range of about 0.1 to 2 wt.%, and its layer thickness 0.0005 Is 0.127 mm.

According to a further preferred, special embodiment, a number of impregnated glass fabric layers are provided, the resin being the reaction product of benzophenone tetracarboxylic acid dianhydride. and m-phenylenediarain is and disperses about $ 0.5 to $ 20? "/ ooi total weight of the dianhydride and diamine components contains inert, heat-resistant, colloidal particles, nickel or copper foil is adhesively bonded to the substrate and a coating of nickel / boron alloy is present on the foil, which has a boron content in the range of 0, 1 to 2 wt. ^, based on the alloy, and a thickness of about 0.00254 to 0.025 mm ² J- has, in a particularly preferred manner, the colloidal particles are silica particles in a concentration of 2 to 12 wt.% are present.

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Claims (1)

PC-5742 March 1, 1972 Claim Laminated article with an inner substrate which has at least one layer of fibrous sheet material which is impregnated with a polymeric precursor of a polyimide resin, the resin being the reaction product of an anhydride component and an amine component, and a conductive metal, which is at least in part is bonded to a surface of the inner substrate, characterized by a substantially continuous nickel / boron alloy coating on the conductive metal part, the alloy having a boron content of about 0.1 to 15 %, based on the weight of the alloy. - 14 1 209839/1059