DD297529A5 - METHOD FOR PRODUCING HIGH QUALITY PCB BASE MATERIALS - Google Patents

Abstract

The invention relates to a rational process for the production of high-quality PF-paper FR 2-VO for electrical engineering / electronics over the way Einstufenimpraegnierung the Traegermaterials. The use of a single-stage impregnation process doubles the work productivity of the Impraegnieren working stage, reduces the use of raw materials and significantly reduces the accumulation of waste products. According to the invention, the object is achieved by mixing a low molecular weight PF resole with a relatively high molecular weight, tungsten-modified resole containing further plasticizers and flameproofing agents to form a homogeneous, clear solution to which further modifying components can be added. The effect of the impregnation mixture according to the invention is attributable to the fact that the mobility of the mononuclear hydroxymethylphenols is increased by the presence of water in the solution, so that selective traversing of the carrier material takes place. Einstufenimpraegnierung; cellulose-containing carrier material; homogeneous PF impregion mixture; low molecular weight PF resole; high molecular weight, with tung oil modified resole; selective penetration of small molecules}

Description

Field of application of the invention

The invention relates to a rational process for the production of high-quality PF paper for electrical engineering / electronics via the way of the single-stage impregnation of the carrier material. PF printed circuit board base material produced by the process according to the invention is characterized not only by good stampability and flame retardancy, but above all by high dimensional stability, so that it is possible to assemble printed circuit boards produced therefrom with the highly effective SMD technology.

Characteristic of the known state of the art

PF-paper based electrical insulating laminates are made by impregnating specialty absorbent papers such as soda kraft paper or cotton paperboard with PF resin impregnation solutions, then drying, stacking multiple impregnated sheets (prepregs) and then pre-pressing at elevated temperature. Depending on the application in electrical engineering, a distinction is made between a wide range of PF hard papers, each with a standardized property level and corresponding price. Of crucial importance to the quality of the PF hard paper is the support material used, the chemical composition of the PF impregnation resins, the process of impregnation (prepreg formation process) and the press conditions for making the laminate. High-quality PF paper requires absorbent papers with low electrolyte content, a PF impregnated resin system optimized in its chemical composition with numerous modification components and optimized impregnation and pressing conditions.

Special experience is needed to produce PF-Kraft FR 2-VO, which is also easy to punch at room temperature and has a high dimensional stability, but at the same time environmental protection issues have to be considered more and more. This high base material quality can only be obtained by using a plurality of resins which differ significantly in their chemical composition and thus in their function, which during the impregnation process lead to the formation of an ordered prepreg structure as a prerequisite for a homogeneous paper / resin matrix composite. It is well known in the art to achieve this targeted prepreg structure by a two-step impregnation process, while producing lower grade PF papers in a one step impregnation process. In a first impregnation step, the preimpregnation, the paper is treated with a low molecular weight, predominantly mononuclear hydroxymethylphenols containing, water-soluble PF resole, which may be blended with amino resins treated. The mononuclear hydroxymethylphenols diffuse into the interior of the paper and interact there with cellulose hydroxyl groups (Plaste and Kautschuk 36 [1989] 1, p. 24-26). In a second impregnation step, the main impregnation or topcoat, the preimpregnated paper web is passed through a higher molecular weight, highly modified, organic solvent diluted PF resin which forms a coating and after prepressing the actual resin matrix. If this structure is disturbed, then there is a significant drop in various laminate characteristics (Acta Polymerica 39 [1988] 8, p. 464/68). The procedure described leads, for example, in DD-WP273603 to kaltsianzbarom, hard-combustible, dimensionally stable base material FR 2-VO. This two-step impregnation process is technically complex and has substantial advantages over a one-step impregnation process, such as

- lower labor productivity (50%),

- additional load on the impregnation machines (reduction of the production volume),

- higher use of raw materials,

- significantly higher accumulation of waste products.

For this reason, there are always efforts to produce FR 2-VO base material by one-step impregnation. The attempt to use only the cover resin for impregnation, is doomed to failure from the outset. Darn-modified, higher molecular weight resins contain even low molecular weight components, but these sirvj due to intermolecular interactions, especially of hydrogen bonds over the phenolic hydroxyl groups by associative formation in their mobility greatly limited. The consequence is that these low molecular components do not diffuse into the interior of the paper. The properties of laminates produced in this way are far outside the standard ranges defined in standards.

Repeated attempts have been made to mix low molecular weight PF resins with higher molecular weight cover resins and to carry out a one-stage impregnation with this mixture. For example, DD-WP226420, DD-WP227823 or DD-WP225669 mix low molecular weight, water-dilutable resols with higher molecular weight, wood oil-modified resoles, and these mixtures are used for single-stage impregnation. Although PF papers produced by the method have a fairly good characteristic image, a considerable disadvantage is that the impregnating mixtures used are not stable. In a very short time it comes in the impregnation tank to complete segregation to form multiple phases. Such mixtures are rejected by the laminate manufacturer as technically unmanageable. The attempt to stabilize these mixtures, for example by addition of surfactant, has hitherto not led to the desired success.

Object of the invention

It is the object of the invention to develop a cost-effective, in the existing systems of the laminate producers feasible process for the production of high-quality PF circuit board base material, which eliminates significant disadvantages of the known technical solutions. By applying a one-step impregnation process, the work productivity in the impregnation step should be doubled, in addition, the use of raw materials should be reduced and the accumulation of waste products should be significantly reduced. The base material FR 2-VO produced according to the new method, which fulfills the characteristics specified in standard sheets, should also be able to be stamped well at room temperature, have a high o-dimensional stability and be suitable for SMD technology.

Explanation of the essence of the invention

The object of the invention is the production of high quality printed circuit board base materials by using homogeneous PF impregnating mixtures, consisting of low molecular weight PF resin components, especially in Einkernbereich and higher molecular weight, modified with unsaturated oils PF resin components, wherein by water input of the Einkernverbindungen one in the Paper interior is reached.

According to the invention, this object is achieved in that cellulose-containing carrier material, preferably cotton, with a basis weight between 75 to 150g / m ² , is impregnated in a impregnation step with a homogeneous PF impregnation, whereby by the nature of the PF impregnation a selective penetration of low molecular weight components guaranteed in the paper inside at impregnation speeds between 5-25m / min. During the entire impregnation process there is no resin segregation, the chemical composition of the PF impregnation mixture remains essentially unchanged. The impregnated paper is dried in a drying tunnel at temperatures between 423 to 459K, wherein the resin content after drying should be 100 to 135% by weight, based on the starting material of the carrier material. The prepreg material is cut to size, stacked and pressed together with adhesive-coated copper foil in a known manner at 423 to 458K and 6 to 10 MPa to base material. The prepreg material can be combined so that outer layers and core layers differ in the composition of their starting resins, e.g. B. to achieve halogen-free or harder cover layers. The PF impregnation mixtures to be used are composed as follows: A low molecular weight PF kesol which is infinitely miscible with water in a ratio of 1: 2 to 1 is mixed with a higher molecular weight tung oil-modified resole containing further plasticizer and flame retardant in a ratio of 0.1: 1 to 1.5: 1 mixed to a homogeneous, clear solution, the further modifying component wi ^ amino resins and / or inorganic fillers such. B. Sb ₂ O ₃ , TiO ₂ , Al (OH) ₃ and / or red phosphorus can be added.

The low molecular weight resol is a resin based on phenol and / or its homologs and formaldehyde in a molar ratio of 1.0.7 to 1: 3.8 using an ortho-position directing catalyst such as MgO, ZnO, CaO or triethylamine. The resin has a solids content of 40-60% and a water content of 5-60% by weight. The phenol used in the resole is still at least 60% in Einkernbereich ago. The higher molecular weight resole is a tung oil-modified and / or partially brominated tung oil-enhanced resin having increased hydrophilicity achieved by fully reacting the elaevearic acid component of the tung oil with at least one double bond, but more preferably two double bonds, reacted per eleastostearic acid chain. The impregnating mixture to be used has a solids content of 50 to 70% and a B time of 423K from 8 to 15 minutes. The water content is 4-12% by weight. It has been found that in the impregnation process using the PF impregnation mixtures described a selective impregnation of the cellulosic carrier material takes place, wherein the mononuclear resin constituents, which have a high mobility, penetrate into the interior of the paper η and there kw '* ken with the cellulose hydroxyl groups. In contrast, the higher molecular weight PF resin constituents containing modifying components form a closed coating which forms the polymer matrix after curing. Surprising is the high mobility of the mononuclear PF resin constituents in the PF Impregnation Blends of the present invention, which permit rapid and sufficient penetration into the pores of the paper. Such mixtures, which are a clear liquid, are not organic solutions in the thermodynamic sense, i. H. they are not arbitrarily miscible with the "solvents" used, such as alcohols, toluene and water, and when certain amounts of diluent have been exceeded, there are significant irreversible deficiencies due to destroying the associate by the diluent, and a significant proportion of PF resin constituents are precipitated, because it is not really soluble in the said diluents.

However, molecular associates are voluminous structures that are currently hindering penetration into the fiber cavities of the paper. That nevertheless sufficient penetration takes place can only be explained by the fact that the monoclinic compounds which are actually soluble in the diluents (including water) used in the PF impregnation mixtures described are involved in the formation of associates.

Exemplary embodiments Example. 1 Production of the impregnating solution for core layers:

26.5 kg of resin solution made from 162 kg m / p-cresol, 52 kg bromine wood oil, 0.7 kg p-toluenesulfonic acid (adduct formation 40 min at 353 K), 10 kg ammonia (25%), 125 kg formalin (37%) ig) (resin condensation for 50 min under reflux), 70 kg of tricresyl phosphate and 88.5 kg of methanol (B time at 423K11.5min, solids content 63%, viscosity at 493K 255mPa.s) and 14.5kg

Preimpregnating resin, made from 188kg phenol, 178kg formalin (37%) and 0.6kg magnesium oxide, according to the Condensation (60min at 353K) 70kg of the water in the resin solution is removed by vacuum distillation and

were supplemented by 73kg of methanol. (B time at 423 K 5.2 min, solids content 45%, viscosity at 493 K 17mPa · s,

Water dilutability infinite), are stirred to a homogeneous mixture (for characteristics see Table 1). Production of the impregnating solution for outer layers: Similar to the core layer impregnation solution, however, a halogen-free covering resin is used. Single-stage impregnation: Cotton interleaf paper (145g / m ² ) is impregnated on a varnishing machine with the resin mixtures (resin application 120%) and at

433 to 443 K dried to a squeeze of 2.5%.

Laminate production:

4 core layer prepregs are coated with 2 outer layer prepregs and adhesive coated copper foil 25min at 8MPa and 423K

Laminates pressed. Table 1 contains characteristics of the impregnating solution used before the beginning and at the end of the impregnation of three Parallel experiments. Table 1 method of investigation

Start (A) End (E)

Trial 1

Solids content (%) A 61 63 62 e 62 66 64 Viscosity (at 293 K) A 84 66 63 (mPa · s) e 95 92 87 B time (min: s) A 7:33 6:30 6:20 e 7:55 6:29 6:00 elemental composition br A 2.7 2.9 2.8 e 2.6 2.9 2.7 P A 1.4 1.4 1.4 e 1.3 1.4 1.3 Tung oil content (%) A 26.2 25.7 24.2 e 25.4 25.2 25.6 Water content (%) A 6.2 6.8 6.7 e 5.6 6.5 6.6

Table 2 shows laminate properties of composites taken from initial prepreg, prepreg in the middle of the paper web and at the end of the impregnation test * to demonstrate the time independence of the impregnation process and the reproducibility.

Table 2

method of investigation j surface resistivity setpoint Beginning (A) attempt 2 3 (C96 / 40/93) (ohms) (x10 ¹⁰ ) Middle (M) 21 / VO 18 / VO End (E) 1 35 / VO 23 / VO UL94-Tost Dielectric loss factor <50 / VO A 17 / VO 23 / VO 20 / VO (Burn time, s / level) (C 96/40/93) M 22 / VO 31 31 e 28 / VO 30 30 Oxygen Index (%) - A 31 30 31 M 31 1.3 / 1.1 1.5 / 1.1 e 31 1.2 / 1.1 1.4 / 1.2 Elemental composition (%) A 1.4 / 1.2 1.2 / 1.2 1.4 / 1.1 Br / P M 1.4 / 1.2 0.7 0.5 e 1.4 / 1.1 0.7 0.6 Vaulting (60 min at 398 K) <1 A 0.4 0.6 0.6 (Mm) M 0.6 5.9 6.9 e 0.4 10.7 6.8 Shrinkage (60 min at ± 5 3/9 ± 4 A 5.10 10.7 6.10 398K) (%) M 5/11 2.0 1.5 longitudinal / transverse (x 10 ~ ² ) e 5.8 1.8 1.6 Punching behavior (DIN 40802) ^ 2,0 A 1.8 2.0 1.4 M 1.6 70 75 e 1.5 65 70 Shear strength (MPa) <: 80 A 70 70 70 M 75 34 34 e 75 32 37 water absorption S 40 A 30 31 32 (1d / 296K) (mg) M 27 8th 7 e 28 5 6 £ 5 A 7 8th 6 M 9 0.046 0,040 e 5 0.043 0.043 <0.05 A 0,036 0,045 0,045 M 0.031 e 0,042

Example 2 Production of the impregnating solution for cover and core layers:

26.5 kg of covering resin solution (from Example 1 -halogen-free) 10.0 kg of pre-impregnating resin (from Example 1)

2.2 kg melamine resin 2.1 kg Totrabromdian

1.3 kg antimony trioxide

are stirred so that the resin solution is homogeneous and the antimony trioxide is finely dispersed therein. Subsequently, cotton interleaf paper is impregnated as in Example 1, then 6 prepregs are stacked and pressed into laminates with adhesive-coated copper foil for 25 minutes at 8 MPa and 423K. Laminates produced in this way meet the specifications specified in standard sheets.

Claims (2)

1. A process for the preparation of high-quality circuit board base materials with multi-modified PF resins, then pre-pressing the impregnated materials under pressure and heat, characterized in that the cellulose-containing carrier material, preferably cotton interleaf paper, with a basis weight between 75 to 150g / m ² in one Impregnation step with a homogeneous PF impregnation mixture, consisting of a low molecular weight PF resole with a share of at least 60% Einkernverbindungen, a high molecular weight, modified with drying oils, possibly plasticizer and / or flame retardant containing PF resole and water, wherein the mass ratio of both Resins 0.1: 1 to 1.5: 1 and the mass fraction of water 4-12% and the solids content of the mixture is 50-70%, impregnated with a! Impregnation between 5 to 25m / min and then in the drying channel at 423 to 458 K is dried, wherein the resin content after drying 100 to 135% Mas seanteile, based on the starting material of the carrier material, should be. 2. The method according to claim 1, characterized in that the impregnation mixture up to 15% by weight of amino resins, such as melamine, dicyandiamide, urea-formaldehyde resins, but also cocondensates of these compounds with phenol and / or inorganic Anger substances such as Sb ₂ O ₃ , TiO ₂ , Al (OH) ₃ and / or red phosphorus, but also organic flame retardants such as Tetrabromdian or Tetrabromdian-EP resins can be added.