JP3023554B2 - Coating materials for printed wiring boards and printed wiring boards - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Object of the Invention [Industrial Application Field] The present invention relates to a printed wiring board used in the electronics industry and to protect the printed wiring board from the outside air and to insulate between circuits. The present invention relates to a protective material to be used, and more specifically, a coating material for a printed wiring board having a large effect of preventing a migration phenomenon, which is a major factor in the occurrence of failures in electronic elements and electronic components, and a print coated with the coating material. It relates to a wiring board.

[Conventional technology]

In an electronic element or electronic component, when a voltage is applied between insulated metal conductors in the presence of moisture, the metal constituting the conductor is ionized, and the surface or inside of the insulating material has a negative potential. Phenomena often occur in the direction of a conductor at a negative potential and deposit at a conductor at a negative potential.

This phenomenon is called migration phenomenon, and is found in various electronic materials, electronic elements and electronic components such as printed circuit boards, hybrid ICs, thick film circuits, capacitor electrodes and through holes, and impairs the reliability of these devices. This phenomenon is one of the causes, and this phenomenon tends to occur more frequently due to the thinning of wiring, reduction in wiring spacing, and pore formation of through-holes due to recent high integration of electronic elements and electronic components. It is in.

The metals that show the migration phenomenon are silver, copper, tin,
Lead, gold, platinum, palladium, aluminum, etc., most of the metals employed as conductors in electronic circuits correspond to those that ionize and migrate when water is present and a voltage is applied, In addition, some of them migrate when an impurity ion such as halogen is added thereto.

As a method for preventing such a migration phenomenon, the following method has been conventionally attempted.

Prevent electronic elements and electronic components from coming into contact with moisture. Prevents ionization of conductive metal on printed circuit boards. The generated ions are reduced so as not to move. The generated ions are insolubilized with a precipitate forming agent. The generated ions are fixed with a chelating agent or a complex forming agent. Deactivates hydroxyl groups on the surface of materials used for manufacturing electronic elements and electronic components.

Here, is a method of coating the surface of the insulator or the entire substrate with a water-repellent material, such as a fluororesin, but it is practically impossible to completely prevent the conductor portion of the printed circuit board from being exposed. Although relatively effective in technology, it is not a complete solution.

Is a method of alloying a conductive metal of a printed circuit board to increase the ionization potential. For example, there is a method of replacing silver of an electrode with silver-palladium.

However, in order to obtain a sufficient effect, it is necessary to increase the content of palladium, which is disadvantageous in that it is expensive.

In addition, a method of adding copper to a silver or aluminum electrode has been studied, but it has not been possible to obtain a sufficient effect.

Is a method of adding aldehyde, hydroquinone, pyrogallol, hydrazine and the like to a paint or the like applied to a printed wiring board, but these additives are chemically unstable and have a disadvantage that they are easily decomposed by heat or light.

Is a method in which stearic acid, oleic acid, palmitic acid and the like are added in the same manner. However, in recent years, it has been reported that free organic acids are involved in aluminum wiring corrosion.
There is a practical problem.

Is a method of adding an organic substance for forming a chelate or complex, such as triazines, benzidine and egg albumin. However, the functional groups of these compounds are mostly
Most decompose and deactivate above 100 ° C.
Therefore, there is no problem under normal use conditions.However, the use environment itself is 10
It is expected that the temperature will exceed 0 ° C., and there is a limit to the use of complex forming agents and chelating agents in the future.

Is a method of treating a glass fiber, which is a material of a substrate, quartz used as a filler of a coating material for a substrate with a silane coupling agent, but this is only a partial measure.

[Problems to be solved by the invention]

In electronic devices and electronic components, the migration phenomenon that occurs when a voltage is applied between insulated metal conductors in the presence of moisture causes failure of these electronic devices and electronic components. There has been a strong demand for prevention.

The present invention provides a coating material for a printed wiring board having a large effect of preventing a migration phenomenon, and a printed wiring board coated with the coating material.

The failure mode due to the migration phenomenon is generally as follows.

(A) silver, gold, (migration phenomenon occurs in the presence of moisture) such as lead water dissociation H ₂ OH ^{+ +} OH ^- dissociation of oxide dissolution _{2M + H 2 OM 2 O +} H 2 ( anode) oxide of a metal M ₂ O + H ₂ O2MOH2M ^{+ +} 2OH ^- (migration) precipitated M ^{+ +} e ^- M (cathode) (b) gold, silver, palladium, copper (generated migration phenomenon in the presence of moisture and halogen) moisture involvement is the same as (a) oxide dissolved M + Cl metals ^- MCl + e ^- (anode) dissociation of oxide MClM ^{+ +} Cl (migration) precipitated M ⁺ + e ^- but M in M (cathode) above (a) (b) is an example of silver, other metals Have been reported to go through a similar mechanism.

Here, the deposited metal becomes dendritic, grows from the cathode toward the anode, and eventually becomes short-circuited so that current flows between the two electrodes.

Note that a short-circuit here means not only when both electrodes are directly connected, but also when the two electrodes are close to each other and a single substance (ion or hole) having a charge as a conductive substance increases, current flows. Is also short-circuited (generally, a short-circuit occurs when a current of about 300 μA flows (has a resistance value of 10 6 Ω or less)).

(B) Configuration of the Invention [Means for Solving the Problems] The present invention provides a coating material for coating and protecting the surface of a printed wiring board, by incorporating an inorganic ion exchanger having a specific -OH group into the coating material. Is prevented. Specifically, various printed circuit boards and hybrids used by mounting electronic elements and electronic components are used.
In printed wiring boards such as ICs and thick-film circuits, by incorporating inorganic ion exchangers with specific -OH groups into the coating material that covers the surface for protection from the outside air and insulation between circuits. , To prevent the migration phenomenon.

[Action]

In the present invention, the function of an inorganic ion exchanger having an -OH group contained in a coating material for a printed wiring board is roughly divided into the following two.

Migrating metal ionizations such as Ag ⁺ , C
An action of capturing and fixing u ⁺ , Cu ²⁺ , Pb ²⁺ , Sn ²⁺ , Au ^{3+, and the} like with an inorganic cation exchanger having an —OH group having high selective ion adsorption, and not transferring them.

The action of trapping and deactivating impurity ions such as halogen atoms that promote ionization with an inorganic anion exchanger having an —OH group having high selective ion adsorption to these ions.

The ion trapping action of the inorganic ion exchanger having an -OH group used in the present invention is as follows.

The inorganic cation exchanger for metal ion capturing RO ^- H ^+, a metal ion M ⁺ OH ^- expressed in hydroxyl type, the ion exchanger is as follows, to produce water as a result.

^{RO - H + + M + OH} - → RO - M + + H 2 O ... (a) reaction for trapping the ion is the ion exchange reaction, as a feature of the inorganic ion exchanger, hardly reverse reaction takes place, In the case of performing a reverse reaction (desorption reaction of trapped ions), special conditions are often required, and generally, ions once trapped are not easily released.

This RO ^- H ⁺ of bonds RO ^- bond between O-M after became M ⁺ is believed to be because strong covalent.

For ionic impurities such as halogen, an inorganic anion exchanger having a -OH group R ^'+ OH ^-, halogen ions
H ⁺ X ^- Expressed in acid form, it will react as follows, to produce water as a result.

R ′ ⁺ OH ⁻ + H ⁺ X ⁻ → R ′ ⁺ X ⁻ + H ₂ O (b) In the case of a neutral salt, the above-mentioned simultaneous reactions (a) and (b) occur.

^{RO - H + + R '+} OH - + M + X - → RO - M + + R' + X - + H 2 O ... (c) [the inorganic ion exchangers] Inorganic ion exchangers used in the present invention, the configuration component At least one selected from the following specific inorganic ion exchangers having a -OH group.

That is, antimonic acid (Sb ₂ O ₅ .nH) having high selectivity for metal ions such as gold, silver, copper, lead, platinum and cadmium.
₂ O), hydrated oxides of pentavalent metals typified by niobate (Nb ₂ O ₅ .nH ₂ O) and tantalum; insoluble quaternary metals typified by zirconium phosphate with high selectivity for copper and aluminum Valent metal phosphate; hydrated bismuth hydroxide, lead hydroxyapatite having high selectivity for halogen ions; inorganic selected from metal antimonates represented by titanium antimonate, tantalum antimonate, manganese antimonate and tin antimonate It is an ion exchanger.

Among the inorganic ion exchangers having these -OH groups, hydrated oxides of pentavalent metals represented by antimonic acid are silver,
It is excellent in capturing ions of copper, cadmium, lead, gold and platinum, particularly silver ions.

On the other hand, for trapping halide ions, hydrous bismuth oxide and lead hydroxyapatite are useful.
Those substituted with _three groups are particularly excellent, and the hydrous bismuth oxide of the present invention includes such an inorganic ion exchanger in which a part of -OH groups is substituted with an oxyacid group.

These inorganic ion exchangers may be used alone for trapping metal ions, or may be used in combination for trapping halogen ions.

(Coating material)

In the present invention, there is no particular limitation on the coating material to contain the inorganic ion exchanger having an -OH group as long as it is for a printed wiring board, and preferable examples include the following types.

In a rigid printed circuit board, a hybrid IC, a thick film circuit, and the like, in the final finishing process or the component mounting process, a protective material that covers the circuit surface or the component mounted circuit surface (hereinafter, collectively referred to as "overcoat material"). .

Specifically, a protective coating made of acrylic, urethane, epoxy or imide resin used for conformal coating.

Dry film resist made of photosensitive resin film, thermosetting or UV-curable liquid resist and solder resist used as permanent resist, protection made of glass or epoxy resin used for hybrid IC etc. There are a coat paste, a polymer thick film (hereinafter referred to as "PTF"), an insulating paste, and the like. In the case of a flexible circuit board, a material coated for the purpose of maintaining electrical insulation during rotation, protecting the circuit board from rust prevention, dirt, and damage and improving folding resistance (hereinafter collectively referred to as "coverlay"). .

Specifically, a film-type coverlay in which an adhesive is applied to a polyimide, polyester or polyamide insulating film.

A thermosetting or UV-curable liquid coverlay such as an epoxy resin may be used.

In the case of a multilayer printed circuit board, there is a material constituting an insulating layer between inner circuits, for example, an insulating protective paint or a prepreg whose surface protection is at least one of its purposes.

The method of adding an inorganic ion exchanger in the present invention to these may be a general method, for example, dispersion in a resin for constituting a protective coating, dispersion in a resin for constituting a solder resist, dispersion in a protective coat paste, dispersion in a PTF insulating paste. Dispersion of
Dispersion of film-type coverlay into resin for insulating film, dispersion of film-type coverlay to adhesive, dispersion to liquid thermosetting type coverlay resin, liquid
Dispersion into a UV-curable cover lay constituent resin, and the like.

The amount of the inorganic ion exchanger contained in the coating material for a printed wiring board is not particularly limited, but is preferably in a range that does not inhibit other properties of the coating material.

Protective paint constituent resin, solder resist constituent resin, protective coat paste constituent glass component, protective coat paste constituent resin, PTF insulating paste constituent resin, insulating film constituent resin in film type coverlay, liquid thermosetting type coverlay constituent resin, When it is contained in a liquid UV-curable coverlay constituent resin or the like, it is preferably 0.1 to 25% by weight, more preferably 0.1 to 10% by weight, based on the constituent resin or constituent glass. If the amount is less than 0.1 part by weight, the effect of ion capture will not be exhibited, and if it exceeds 25% by weight, the insulating property of the coating material may be impaired, which is not preferable.

When it is contained in the adhesive of the film type coverlay, it is preferably 0.1 to 15% by weight, more preferably 0.1 to 10% by weight, based on the adhesive.

The particle size of the inorganic ion exchanger is preferably finer in order to increase the ion trapping rate and contact with the target ion, and the average particle size is preferably 10 μm or less, more preferably 5 μm or less.

[Printed wiring board]

In the present invention, there are the following printed wiring boards coated with a coating material containing an inorganic ion exchanger having an -OH group.

Rigid printed circuit boards, hybrid ICs, thick film circuits, etc., whose coating material is an overcoat material.

 A flexible circuit board whose covering material is a coverlay.

A multilayer printed circuit board, wherein the covering material is a material constituting an insulating layer between inner layer circuits.

(Examples and Comparative Examples)

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. In the examples, "%" means "% by weight",
“Parts” means parts by weight.

Examples 1 to 4 and Comparative Example 1 A commercially available silver paste is applied to a glass-epoxy resin laminate by a screen printing method, and is heated and cured at a predetermined temperature to form two facing comb-shaped parts as shown in FIG. A printed wiring conductor was formed.

Separately, a mixture (1: 1 by weight) of zirconium phosphate as an inorganic ion exchanger having an -OH group for trapping metal ions and lead hydroxyapatite for trapping halogen ions was added to 100 parts of the epoxy resin. , 1, 5, 10 and 20 parts were mixed to obtain 5 kinds of resin liquids. These resin liquids were applied to the surface of the glass epoxy resin laminate after the above-described printed conductor was formed except for the terminal portions indicated by A and B in the first time, and were cured by heating to provide a protective coating.

The silver migration phenomenon was measured by applying a DC voltage of 100 V to the two comb electrodes shown in FIG.
The resistance was maintained at 95% RH, and the change in resistance between the electrodes was measured over time. The point in time when the resistance dropped to 10 ⁶ Ω was used as an index of failure due to migration.

 Table 1 shows the results.

Examples 5 to 8 and Comparative Example 2 For 100 parts of an epoxy adhesive used for a coverlay for a flexible circuit board, as an inorganic ion exchanger having an -OH group for capturing metal ions, for capturing antimonic acid and halogen ions. A mixture of hydrated bismuth oxide containing NO ₃ groups (functional group ratio, OH groups: NO ₃ groups = 5: 1) (weight ratio 7:
0), 1, 5, 10 and 15 parts of 3) were added to obtain five different adhesives. Each was applied to a polyimide film to form a B-stage, thereby forming a coverlay for a flexible circuit board.

Separately, five circuit boards having conductors (electrodes) as shown in FIG. 1 formed by subjecting a copper clad board for a flexible circuit board using a polyimide resin to a base film to an etching treatment were prepared.

Each of the above five coverlays was mounted on the surface of a circuit board and bonded by a hot press method to obtain five kinds of flexible circuit boards.

For the measurement of the silver migration phenomenon, a DC voltage of 500 V was applied between the electrodes, and the insulation resistance between the electrodes, which was maintained at 80 ° C. and 86% RH and changed with time, was measured. Table 2 shows the results.

However, the time to short circuit here is the insulation resistance value of 16 ⁶
It refers to the point when the voltage falls below Ω.

Examples 9 to 12 and Comparative Example 3 A mixture of titanium antimonate as an inorganic ion exchanger having an -OH group for capturing metal ions and lead hydroxyapatite for capturing halogen ions (weight ratio: 6:
4) to 0,0.1,1,5,10 for 100 parts of epoxy resin paint
Were added and kneaded well to obtain five different coatings for forming an insulating layer. FIG. 2 is a cross-sectional view of the test pieces of the present example and the comparative example. 5000 pieces of wiring conductor layers 22a and 22b formed by etching the copper foil of the glass epoxy laminate 21 were prepared. The insulating layer 23 was formed by screen-printing and heating and hardening the above-mentioned five types of epoxy-based paints, one for each of the above-mentioned five types, so as to cover the wiring conductor layer 22b. The thickness of the insulating layer is about 20 μm. Next, a conductive paste containing copper powder was printed so that one end thereof was in contact with the wiring conductor layer 22a, and baked to form a second wiring conductor layer 24 facing the wiring conductor layer 22b. Finally, wiring conductor layer with epoxy resin
A protective layer 25 was printed so as to cover 24, and was cured by heating to obtain a test piece for measuring migration between insulating layers of the multilayer printed circuit board. A total of 5,000 test pieces, each with five different types of insulating layers, prepared as described above, were tested at a temperature of 5,000.
Place it in an atmosphere at 40 ° C and a relative humidity of 95%.
DC voltage 2 so that the positive side is the positive side and the wiring conductor layer 22b is the negative side.
00V was applied to measure the insulation resistance deterioration between the insulating layers.

 Table 3 shows the results.

Table 3 shows the number of those having an insulation resistance of 200 MΩ or less for 1000 pieces in each example. From this table, it is clear that the insulating layer of the example prevents migration of copper.

(C) Effect of the Invention By using the coating material containing the inorganic ion exchanger having -OH of the present invention, it is possible to prevent the migration phenomenon, which is a problem as a cause of failure of electronic components and electronic elements. As a result, an electronic device having higher reliability than before can be obtained.

[Brief description of the drawings]

FIG. 1 shows patterns of printed wiring conductors (electrodes) used in Examples 1 to 8 and Comparative Examples 1 and 2 of the present invention. Here, the shortest distance between the electrodes is 1 mm in each case. A, B ... Terminal portions for connection to an external power supply (A and B are either + and the other is-) FIG. 2 is used in Examples 9 to 12 and Comparative Example 3 of the present invention. It is a figure showing the structure of the test piece which was put. 21 glass-epoxy resin laminates 22a, 22b first conductive layer 23 insulating layer 24 second conductive layer 25 protective layer

────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification symbol FI H01L 23/31 H01L 23/30 R H05K 3/28 (56) References JP-A-62-192444 (JP, A) JP-A Sho 60-226147 (JP, A) JP-A-58-176237 (JP, A) JP-A-60-43896 (JP, A)

Claims (2)

(57) [Claims] (1) at least one selected from the group consisting of a hydrated oxide of a pentavalent metal, an insoluble tetravalent metal phosphate, a hydrated bismuth, lead hydroxyapatite and a metal antimonate;
A coating material for printed wiring boards, comprising an inorganic ion exchanger having an OH group. 2. An at least one selected from the group consisting of hydrated oxides of pentavalent metals, insoluble tetravalent metal phosphates, hydrated bismuth, lead hydroxyapatite and metal antimonates.
A printed wiring board coated with a coating material containing an inorganic ion exchanger having an OH group.