DE3437967A1 - METHOD FOR PRODUCING A LAMINATE - Google Patents

Description

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PAT E N TAN WA LT D-4OOO DÜSSELDORF 1 · SCHADOWPLATZ 9

VNR: 109126

Düsseldorf, October 12, 1984 & 442

W.estinghouse Electric Corporation
Pittsburgh, Pa. 15222, USA

Method of making a laminate

The invention relates to a method for producing a laminate. Copper clad laminates for use in Manufacture of printed circuit cards consist of very thin copper foil that is on or on top of both sides of a laminate is applied, which laminate consists of a fabric or a mat that is in an organic resin is embedded. Printed circuit cards are made from the copper-clad laminates made by removing certain portions of the copper to make electrical paths, and that then integrated circuits or other electrical components on the circuit board or board to be assembled.

It has been found that sometimes printed circuit board failures occur by that very much thin cracks ("microcracks") occur which form within the printed circuit board. These jumps the electrical paths made of copper can break or allow moisture to enter,

whereby the copper can peel off or a short circuit occurs. While the size of the components and the width As the copper electrical path is reduced year by year, the printed circuit boards are more and more fragile versus failure due to microcracks. This is particularly a problem for printed circuit boards, which are used in soaring aircraft because they alternate between very hot temperatures on the ground and very cold temperatures occur at high altitudes. These cyclical thermal loads greatly increase the Formation of microcracks and the likelihood that the circuit will fail.

Due to their light weight, the laminates are also used as structural components in aircraft. the Formation of microcracks or microcracks in a structural part can act as a point from which the crack can emerge propagates, resulting in failure of the part under mechanical stress.

For these reasons, reducing the formation of microcracks in laminates is a major problem To look at meaning.

The object of the present invention is to reduce this cracking.

According to the invention, this is achieved by a method in which a laminate is produced in that a fabric or a mat of an amide or a crystalline Polyester impregnated with a liquid organic resin and then the impregnated fabric or the impregnated mat is formed into a laminate, the fabric or mat prior to impregnation active oxygen- or nitrogen-containing gas plasma for exposed for a period of 1 to 40 minutes, at a ratio of radio frequency power (in watts) to

Flow rate (in cm ³ / minute) from 1 to 4, a gas pressure from 0.1 to 5 mm Hg, and a frequency from 100 Hz to 1 GHz.

It has been found that the formation of microcracks in certain types of laminates commonly used for printed Circuit boards are used, as well as in structural components in aircraft greatly reduced can be achieved if the fabric or mat from which the laminate is formed is adhered to a gas plasma is exposed to certain critical parameters before they are incorporated into the laminate. Although the present Invention is not to be limited by any theories, it should be noted that it is believed that by exposing the fabric or mat to a gas plasma at the critical parameters, a chemical bond is created between the fabric and the resin, which leads to a significant improvement in the Shear strength of the laminate leads. As a result, both the size and the frequency of the microcracks become reduced.

In the method according to the invention, a reinforcement layer or substrate, typically a fabric or mat, treated with a gas plasma before using impregnated with a resin and formed into a laminate. The fabric or mat can be any amide or mat crystalline polyester fiber. This includes Polyethylene terephthalate, butylene terephthalate, poly (P-phenylene terephthalamide) and nylon such as nylon 66, nylon 6, and nylon 12. Aramids such as Poly- (P-phenylene-terephthalamide) are preferred because they are most common as substrates for printed circuit boards which are subject to the microcrack problem. The fibers that are typically oriented and consist of high-crystalline fibers, have a diameter of 1 to 20 microns, are spun around

to form a yarn, which is woven to form a fabric or laid to form a mat. That The method according to the invention can only be applied to fabrics or mats, not to the fibers, since more material is treated can be applied to a fabric or mat, and a treated thread does not occur quickly enough after plasma treatment can be used to prevent the effects of the plasma treatment from volatilizing again.

The fabric or mat is treated by placing it in a capacitively coupled gas plasma unit is arranged. The plasma unit is capacitively coupled instead of being inductively coupled there it is believed that capacitive coupling produces a more uniform radio frequency (RF) field. That Plasma can be formed using any inorganic gas containing an active oxygen or Has a nitrogen content, such as SO, NO, NO, N, 0, or NH. Nitrogen, oxygen or ammonia are preferred and oxygen is the cheapest since oxygen has been found to work best.

The ionization of the gas must occur under certain critical parameters if the plasma treatment is to be effective. First, the radio frequency power (in watts) and the flow rate (in cm ³ / minute) must be between about 1 and 4, because if the ratio is less than 1, the gas has a very low reactivity, while if the ratio is greater than 4 the tissue could be destroyed. The gas pressure should be between 0.1 and 5 mm of mercury. Pressures less than 0.1 mm result in a gas with lower activity, while at pressures above 5 mm Hg the tissue begins to degrade. The radio frequency of the gas plasma should be between 10 0 Hz and 1 GHz, as very few ions are produced at frequencies below 100 Hz and

frequencies above 1 GHz destroy the tissue. The mesh should remain in the gas plasma for 1 to 40 minutes. A smaller residence time is ineffective and a larger one Dwell time no longer creates any additional beneficial effects. Finally, the fabric is preferably placed in the Laminate inserted within 1 month after treatment with the gas plasma, as the effectiveness of the treatment tends to decrease after this time.

A layer suitable for a laminate is made by impregnating the treated fabric with a liquid organic resin. Typically, the layer, as well as the laminates made from a plurality of layers, have a resin content of 35 to 60 %. The resin can be liquefied by heating, or it can be a resin that is liquid at room temperature, or it can be a solid dissolved in a solvent. Resins having a fusible B-stage are most commonly used. Resins useful in the present invention include epoxy resins and polyimide resins. Polyimide resins include polymaleimides, amide-imides, and polyamide-imide resins. Epoxy resins are preferred because they are most commonly used for printed circuit boards that are subject to microcracking.

The laminates are usually made by consolidating a plurality of resin impregnated layers using heat and pressure. While the laminates are made in some form can, thinner laminates are more exposed to microcracking and therefore get the larger one Benefit from the method according to the invention. When the laminate is used to form a circuit board, be thin copper layers on one or both Sides of the laminate applied. Printed circuit boards that are very high for integrated circuits

Speed (VHSIC = Very High Speed Integrated Circuits) are of particular benefit from the treatment according to the present invention, since the components of these circuit boards are very close to one another and are therefore very sensitive to microcracking. It should be taken into account that a single layer of resin-impregnated fabric or mat can be used, rather than a plurality of such laminated layers.

The invention will now be explained in more detail using the following examples:

example 1

Pieces of 352-web style fabric supplied by the US company Clark-Schwebel under the designation "Kevlar CS800" which is believed to be made of poly (P-phenylene-terephthalamide) were manufactured according to US Pat American method ASTM D-18 76 tested. Two pieces of fabric were bonded together using a polyamide cured epoxy resin sold by Hughson Chemical under the trade designation "Chemlok 305". At least 8 copy samples were examined for each treatment condition. A capacitively coupled oxygen plasma unit delivered an oxygen plasma of 0.7 mm mercury, 100 watts of radio frequency power at an oxygen flow rate of 30 cm ³ / minute. The tissues were exposed to the oxygen plasma for various times, then bonded together with the aid of the resin, which resin was then cured at 100 ° C. for one hour. The samples were allowed to cool and adjust to ambient conditions for at least 16 hours prior to testing. The two pieces of fabric were then pulled apart and the peel strength measured. The following table gives the results:

sample Duration of Plasma Peel strength ) g / cm) (lbs / in) No. plot (Minutes) (5.55 + 0.93 1 0 6.24 + 0.79 2 10 7.06 + 0.88 3 30th 8.24 + 0.70 4th 60 8.16

The above table shows that the adhesion with the treatment time increases with the oxygen plasma up to about 30 minutes.

Example 2

An epoxy resin was formed from 10% by weight diethylene triamine and 100% by weight of a liquid epoxy resin sold by the Dow Chemical Company under the trade designation DER 332, the latter being believed to be pure diglycidyl ether of bisphenol A having an epoxy equivalent weight of 172 to 176 is. The Kevlar fabric described in Example 1 was exposed to the oxygen plasma described in Example 1 for 30 minutes for each side and then impregnated with the epoxy resin formulation. Fifteen strands of the impregnated Kevlar fabric were then stacked on top of one another and laminated ^{in a press for 10 minutes at 85 ° C. and 0.7 N / mm 2.} The laminate was then allowed to cool to room temperature and adjust to ambient conditions for 16 hours. 4.44 cm by 0.63 cm test samples were then cut from the 0.63 cm thick laminate and examined according to US Standard ASTM D-2,344. A set of control samples that had not been treated with the oxygen plasma were also tested under the same conditions. The test consisted of placing the pieces of laminate between two beams and measuring the force required by a third beam pressing in the middle to break the laminate. The following table shows the results:

- 10 - 3437967 Oxygen plasma treated control (0.0069 N / mm ² ) (0.0069 N / mm ² ) 4872 3690 5050 3400 4940 3580 4810 3555 4810 3000 4850 4110 4700 3570 4890 3850 4724 3290 4630 3780 4828 + 3% By 35 83 + 9% cut + <3

The table above shows that those with oxygen plasma treated samples showed a clear improvement in terms of short beam shear strength.

Example 3

The Kevlar fabric described in Example 1 was treated with the oxygen plasma described in Example 1 using 100 W radio frequency power for 30 minutes at a flow rate of 30 cm ³ / minute. After treatment, the fabric was immersed in a NEMA Grade FR4 epoxy resin used by Westinghouse for commercial laminates. The treated strands of fabric were then B-staged in a hot air oven at 150 ° C for 7.5 minutes and then laminated together to form a composite panel. The same procedure was followed using untreated Kevlar fabric. Prior to resin impregnation, each fabric piece of Kevlar fabric, both treated and untreated, was weighed and the weight recorded. After each one cures

Laminates were weighed and the resin content calculated using the following equation:

η
Laminate weight - Σ (fabric weights) χ 100 laminate weight

The resin content of both cases is given in the following table:

Kevl ar treatment resin content

O ₂ plasma treatment (30 ply) 45.6% untreated (30 ply) 37.7%

The table above shows that there was an 8% increase in resin content for the laminate obtained from the Oxygen treated fabric was compared with the laminates made from untreated Kevlar fabric were manufactured.

One 1.3 2.6 cm section of each Laminate was thermally treated cyclically, with 30 cycles from -8 0 ° C to 150 ° C, in order to reduce the influence of the Oxygen plasma treated tissue reinforcement to identify the microcracking of epoxy / kevlar laminates usually occur with the FR4 resin system. A scanning electron microscope was used when examining used to determine the number and severity of microcracking. At HX magnification there were none Cracks visible within the Kevlar laminate during oxygen plasma treatment, but the breaks were clear visible on the untreated laminates. At 550x, some microcracks became apparent in the The treated laminates were visible as well as the untreated laminates, but the formation of fractures was visible in the Plasma treated laminates are just beginning.

Also, the degree of fracture in terms of size and number was not as severe in those with oxygen plasma treated laminate as with the untreated laminate. Figures 1 and 2 are scanning electron micrograph representations with 55X magnification for the laminate made with untreated or treated fabric became. The lines labeled A and B in Figures 1 and 2, respectively, are micro-breaks.

Example 4

Kevlar laminates are known for their hygroscopic properties Characteristic. For this reason, Kevlar laminates usually suffer severe degradation in humid environments. About the influence of the oxygen plasma treatment on Kevlar with regard to the mechanical properties of Kevlar / epoxy laminates to investigate, laminates were formed, both treated with oxygen plasma and untreated Kevlar was also used, as described in the previous examples, whereupon the Samples were subjected to a 5 day water boil test. After this heavy use, the Laminates were tested for interlaminar shear strength using methods described in US Pat American standard ASTM D-2344. A control sample for each laminate (no water decoction) was set was also examined at that time. The following table gives the results again:

Kettle Shear strength N / mm ² + 6) Kevlar treatment treatment (0.0069 + 7% 0 plasma treatment no 4814 + 6% 0 plasma treatment Yes 5030 + 8% untreated no 3892 + 21% untreated Yes 3240

The above table shows that there is a serious deterioration in the shear strength due to the weakening the Kevlar fiber / resin interfacial adhesion in the untreated Kevlar reinforced laminate becomes visible, but not in the oxygen plasma treated Kevlar / epoxy laminates. There is further evidence of a weakening of the interlaminar adhesion after the water boil treatment the huge increase in the data spread, as measured by the standard deviation, which was found for the laminate without treated Kevlar could be observed, but not the treated laminate.

Example 5

About the oxygen plasma treatment of Kevlar in large-scale applications To be able to take advantage of the beneficial effects of plasma treatment in production operations be long-lasting, so that they can be used in a wide range of applications allow for resin impregnation of the fabric. This lies because treated fibers have to wait hours after plasma treatment to be impregnated with resin will. Kevlar fabric was made with oxygen plasma like treated as described above, but it was then stored in a dryer, the Drie-Rite (calcium carbonate) and atmospheric air for 44 hours before sample preparation took place. the Bond strength of treated as well as untreated Kevlar as well as treated Kevlar that had been aged was measured using the T-Shear Test, U.S. Standard ASTM D-18 76. Chemlok 305 epoxy resin was used as a resin binder. The results of these tests are shown in the table below reproduced:

Peel strength d. Plasma loading

Samples after aging before treatment were peel strength 0 hours 4 hours 44 hours (0.178 kg / cm width) aging aging aging

6.24 + 0.93 8.3 + 0.83 8.57 + 1.0 8.71 + 0.88

The table above shows that there are no differences between the oxygen plasma treated Kevlar samples that were aged in the dryer prior to bonding versus those that were aged immediately after plasma treatment were bound. In both cases, the bond strength was significantly greater than in the untreated Rehearse. Electron spectroscopy for chemical analysis confirmed these results by at times sharp increase in the ratio of oxygen / carbon and oxygen / nitrogen on the Kevlar fiber surface was shown. This indicates that a chemical change has occurred in the surface chemistry of the fibers that shouldn't go away immediately. It is believed that oxygen plasma treatment of Kevlar fibers derivatives of poly (p-phenylene-terephthalamide) molecules modified by oxygen on the fiber surface.

ES / where 4

Claims (4)

drying. Ernst Stratmann 3A37967 PATENTANWALT D-4000 DÜSSELDORF 1 · SCHADOWPLATZ 9 VNR: 109126 Düsseldorf, October 12, 1984 8442 Westinghouse Electric Corporation Pittsburgh, Pa. 15222, USA patent claims: 1. A process for producing a laminate, consisting of impregnating an amide or crystalline polyester fabric or mat with liquid organic resin and forming the impregnated fabric or mat into a laminate, characterized in that the fabric or mat is an active oxygen prior to impregnation - or nitrogen-containing gas plasma for a period of 1 to 40 minutes at a gas pressure of 0.1 to 5 mm Hg, a frequency of 100 Hz to 1 GHz and a ratio of radio frequency power (in watts) to the flow rate (in cm ³ / minute) from about 1 to 4 is exposed. 2. The method according to claim 1, characterized in that the gas plasma consists of oxygen, nitrogen, ammonia or mixtures thereof. 3. The method according to claim 1 or 2, characterized in that the resin is an epoxy resin or a polyimide resin is. 4. The method according to claim 1, 2 or 3, characterized in that the fabric or the mat made of poly (P-phenylene-terephthalamide) is. ES / where 4