Technical Field The present invention relates to an improved heat conducting system employing a separator and a side heat-conducting unit closely contacted to a side of the heat conductive separators to additionally guide heat transfer to platens positioned above and below the stack of laminates, in which a heat conducting layer made of material having high thermal conductivity is embedded in a conventional separator widely used in lamination processes to produce metal clad laminates, multilayer printed circuit boards and unclad laminates. The heat conducting system enables the heat transfer to the platens through the sides of the stack of laminates, including heat flow to upper and lower directions, thereby minimizing temperature difference among the laminates in the stack.

More particularly, the lamination process takes the conventional process of disposing a stack of materials to be laminated and separators between the upper and lower platens, and followed by heating and pressurizing processes. The difference is that the separator used in the present invention has an embedded heat conducting layer in a conventional metal separator which enables additional heat flow through a side heat-conducting unit closely contacted to the sides of the heat conducting separators, thereby rapidly cooling the laminates and minimizing maximum temperature difference among the laminates.

Instead of employing the above separator with the embedded heat conducting layer, the present invention may employ a direct heating separator, which has an electrical heating means, and a side heat-conducting unit. In the case of employing the direct heating separator, electrical energy is transferred to the laminates through an electrical connector. Simultaneously, heat of the laminates is quickly conducted to the upper and lower platens through electrical connectors

placed in each one side of a separator, thereby reducing the temperature differences among the laminates during the cooling process, which allows improved uniformity in physical properties (for example, dimensional stability) of the fabricated laminates. In that case, the side heat- conducting unit is closely contacted to the sides other than where there is an electrical connector. heating, thereby additionally guiding the heat flow through the sides. As a result, the temperature difference among the laminates is reduced.

The separator used in the lamination industry is generally interposed between the laminates so as to separate the consolidated laminates from one another and to smooth the surfaces of the laminates. To this end, a stainless steel plate or aluminum plate having 1.0 mm to 2.5 mm thickness is commonly used. In the industry, the term"laminate"commonly refers to a book of raw materials to be laminated or to a laminate consolidated under heated and pressurized conditions. In reality, a plurality of books of raw materials to be laminated and separators is interposed between the platens, and heated and pressurized to consolidate the books to laminates in one lamination cycle.

The present invention also relates to an improved heat conducting system to minimize the maximum temperature difference among laminates during a lamination cycle.

Background Art Recently, there has been a trend towards thinning and miniaturizing electronic circuit boards. Therefore, a demand for precision in processing the circuit boards is continuing to grow.

In view of the precision needed in an electronic circuit, dimensional stability due to contraction/expansion of a printed circuit board along with circuit fabricating processes is considered one of the most important parameters. The term"dimensional stability"refers herein to a precisely predictable range of movement on a coordinate system of the laminate which comes from thermal and mechanical stresses inevitably embedded in during lamination processes.

If the dimensional stability of a printed circuit board is not secured, the interconnection among

the circuits cannot be made properly as a result of the inaccuracy in the prediction of the movement of coordinates system of the printed circuit board. The stress embedded in a printed circuit board makes the coordinate of the board move continuously along with the fabrication processes. But it is well known in the industry that the amount of stress level in a board is different from board to board. The reason why the amount of stress embedment is different from one board to another comes from the heating and cooling speed of the laminates. In particular, the difference in the cooling speed of each laminate makes laminates with different level of stress embedment in the laminates. If the pressure acting on the laminate and the separator is decreased to reduce the stress applied to the laminate, the time demanded to perform the cooling process is delayed, thereby reducing the productivity. In order to secure a laminate of high dimensional stability, it is necessary to reduce the differences in cooling speeds of the laminates. Specifically, the less the difference in the cooling speeds is among the laminates during cooling process, the higher the dimensional stability of the manufactured laminate becomes. Due to the above reasons, it is inevitable to improve the heat conducting processes in the conventional method of manufacturing the laminate.

Most of modern fine line circuits used electronic industry consist of a multilayer circuit, and have dozens of drilled holes of around 0.2 mm in diameter per one square centimeter to interconnect the layers. In addition, dimensions of an interlayer connecting land having drilled holes are reduced to maximize the area utilization of a circuit board. In consideration of the above trend, it is believed that the diameter will further be reduced to as small as 0.001 inch in diameter or less. Taking this trend into consideration, it is very important to precisely predict the position of the respective circuits. If the accuracy in the prediction of the circuit coordinate is lowered, there is a greater possibility that the interconnection among the interconnection holes in a circuit board may be improperly made, thereby causing a higher defective rate and resulting in increased manufacturing cost of the circuit board.

The conventional system uses platens located at the top and bottom of the stack of books

of laminate and separator to heat and pressurize the stack. Once the laminates are fully cured, cooling water or cooling medium is supplied to the upper and lower platens to cool the laminates.

In order to reduce the manufacturing cost in the laminating process employing the above method, several laminates are deposed in between the platens as shown in FIG. 7. At that time, a metal separator is interposed between the laminates to achieve smoothness in the formed product.

(Although FIG. 7 shows that the laminate and separator are separated from each other, the laminate and separator are in close contact due to the pressure applied from the platens) The respective laminates are consolidated into one laminate by heat and pressure. If the consolidation process is completed under heated and pressurized conditions, cooling water or cooling medium is supplied to the platens to cool the formed laminates.

To describe the cooling process in more detail in a conventional cooling process, heat from the laminates is transferred to the platens, which are positioned above and under the laminates and are cooled by the flow of the cooling water, in the direction of the arrow shown in FIG. 7, thereby cooling the consolidated laminates. At that time, in addition to the heat flow to the platens during the cooling process, some of the heat is outwardly radiated from the sides of the laminate, although in small quantity, However, in a conventional cooling process where the heat flows from the cured laminates to the platens, the cooling speed varies depending upon the distance of the laminate from the platens. As a result, the closer the laminate is from the platen, the faster the cooling speed of the laminate is, and vice versa. Maximum temperature difference among the laminates, which are produced by the difference in cooling speed of each laminate, are shown in FIGs. 5 and 6. Detailed description thereof will be hereinafter described in the following embodiments 2-C and 5-C.

The coefficient of the metal separator interposed between the laminates is 4 to 7 ppm/°C, and that of the consolidated laminate of glass fiber reinforced epoxy is 10 to 30 ppm/°C. Stress is embedded in the laminates due to the difference between the thermal expansion coefficients of

the metal separator and the laminate, and the embedded amount of the stress is determined mainly by the cooling speed of the respective laminates, the pressure applied to the laminate and temperature. Therefore, the conventional method of cooling the laminates using platens has a drawback in that the cooling speed of the laminates varies depending upon the position of the laminates in the stack, and the embedded stress varies accordingly, thereby causing dimensional instability of the laminate.

Disclosure of the Invention The inventor has studied the problems involved in the prior art, and discovered that a metallic layer of high heat conductivity is embedded in a conventional metal separator, and a separate side heat-conducting unit having high thermal conductivity is closely contacted to a side of the heat conducting separator, so that heat is not only directly transferred to upper and lower platens as in a conventional cooling process but also to the platens through the heat conducting separator and the side heat-conducting unit, thereby minimizing the temperature difference among the laminates.

Accordingly, it is the object of the present invention to minimize temperature variation among the laminates during a cooling process when laminates interposed between upper and lower platens are cured under a heated and pressurized environment. In order to accomplish the above mentioned object, the present invention employs a separator which has heat conducting layers therein and a separate side heat-conducting unit closely contacted to a side of the separator for additional heat conduction to platens, thereby eliminating the drawbacks contained in a conventional cooling process, as well as maintaining advantages of a conventional cooling process.

Instead of employing the separator with heat conducting layer (s), the present invention may employ a direct heating separator. In the case of employing the direct heating separator, a plurality of separators are interconnected to each other through connecting points. The sides of

the separators which are not provided with the electrical connecting points are closely contacted to the side heat-conducting units, so that it eliminates the drawbacks contained in a conventional cooling process, as well as maintaining advantages of a conventional cooling process.

It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the present invention as claimed.

Brief Description of the Drawings The above objects, other features and advantages of the present invention will become more apparent by describing the preferred embodiment thereof with reference to the accompanying drawings, in which: FIG. 1 is a schematic view illustrating a side heat-conducting unit according to the present invention.

FIG. 2 is a cross-sectional view of a heat conductive separator having a heat conducting layer of high heat conductivity, in which FIG. 2A shows an external heat conducting layer and FIG. 2B shows an internal heat conducting layer.

FIG. 3 is a schematic view illustrating a portion of an improved direct heating separator with a heat conductor coated thereon.

FIG. 4 is a schematic view illustrating a contact-point connecting unit having one side performing electrical connection and the other side performing thermal connection and interposed between direct heating separators.

FIGs. 5 and 6 are graphs showing temperature differences between the most cooled laminate and the least cooled laminate when cooling the cured laminates using the improved heat conducting system according to the present invention.

FIG. 7 is a schematic view illustrating heat flow generated during the cooling cycle in a conventional press work.

FIG. 8 is a schematic view illustrating an arrangement of laminates, a side heat- conducting unit, and a heat conducting separator.

Best Mode for Carrying Out the Invention Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

FIG. 1 is a perspective view of a side heat-conducting unit according to one preferred embodiment of the present invention, in which FIG. 1A shows a front of the side heat-conducting unit and FIG. 1B shows a rear of the side heat-conducting unit. The side heat-conducting unit in Figures 1A and 1B is made of material having good heat conductivity, examples of which may be the same or similar to the heat conducting material embodied in a separator described thereinafter.

The side heat-conducting unit includes a pair of female and male bodies, a resilient member, and a fixing member. The body of the side heat-conducting unit shown in FIG. 1A consists of a female body corresponding to an upper plate 1, and a male body corresponding to a lower plate 2.

Heights of the female and male bodies are varied by the resilient member 3, such as a spring, depending upon the applied pressure, so that when the height of laminates is varied when performing the press work, the height of the side heat-conducting unit is also varied. In the case of the embodiment shown in FIG. 1B, the fixing member 4 is secured to a rear of the male body 2 to closely contact the side heat-conducting unit with a carrier plate (not shown). To this end, the fixing member 4 is provided with a locking member 5 having a spring therein. In the case of additionally cooling the side heat conducting unit of present invention using cooling water and cooling medium, the side heat-conducting unit of the present invention may include a nozzle connected to an external cooling system.

Although the side heat-conducting unit constructed as described above is shown herein, it is not limited to that construction. Any construction thereof may be utilized to achieve the objects of the present invention. In other words, if any construction improves the variations in

the cooling speeds of the laminates through close contact of the side heat-conducting unit and the separator through the locking member 5, those kinds of construction may be contained within the scope of the present invention.

FIG. 2 shows the heat conducting separator with layers of high heat conductivity material of 5 microns to 2 mm embodied either externally or internally in a conventional separator. The thickness of the heat conducting layer is not limited to this range. In FIG. 2, a member indicated by a reference numeral 1 is the material generally used in a conventional separator and serves as a carrier. In the case of the below Example 2-A, a stainless steel plate, an aluminum plate, a copper plate or a steel plate of 0.5 mm to 4 mm in thickness is used, while in the case of the below Example 2-B, a stainless steel plate, an aluminum plate, a copper plate or an iron plate of 0.2 mm to 2 mm in thickness is used, material and thickness of which are not limited thereto.

A member indicated by reference numeral 2 is a heat conducting layer made of material having high conductivity, such as aluminum, iron, bronze, copper, platinum, titanium, zirconium, gold, silver, chromium, rubidium, strontium, molybdenum, ruthenium, palladium, cadmium, tin, antimony, cesium, barium, tungsten, lead, bismuth, alloys thereof, coatings thereof and so forth.

The present invention is not limited to the above components. Considering that the heat conductivity of the stainless steel plate widely used in the art is 140 to 180 btu-in/f-time-°F, the heat conductivity of the heat conducting layer embodied in the separator must be higher than the above level. The case of the Example 2-A uses the heat conducting layer of 0.005 to 2.0 mm in thickness, while the case of the Example 2-B uses the heat conducting layer of 0.05 to 3.0 mm in thickness. The present invention is not limited to this range.

FIG. 3 shows a direct heating separator with a material of high conductivity embodied therein. Examples of the direct heating separators are disclosed in Korean Patent No. 0282861 (Patent Application No. 98-15470), Korean Patent No. 0332086 (Patent Application No. 99- 49535), U. S. Patent No. 6,174, 591 and Japanese Patent Application No. H11-323179. The direct heating separator has an electrically heating member for applying electric energy to the

conventional separator. If the laminates are directly heated by the heating member, variations in thermal properties applied to the laminates is lowered, thereby minimizing variations in prepreg chemorheological properties and the temperature rising speeds of the respective laminates in the stack. The direct heating separator may be commercially available from CSS Technologies Ltd.

Co. of Kuro-dong, Seoul, Korea. The direct heating separator is preferably constructed to be connected electrically and thermally using a contact-point connecting unit shown in FIG. 4, having openings at front and rear of the separator for the connections. In FIG. 3, reference numeral 1 denotes the layer of heat conductor; reference numeral 2 denotes a layer of electric insulator; and reference numeral 3 denotes a layer of a heating circuit of the separator.

FIG. 4 shows the contact-point connecting unit for electrically and thermally connecting the separator, in which the contact-point connecting unit is made of resilient material so that a height thereof may be varied depending upon a thickness variation of the laminates. A copper- beryllium elastic solid or the like is the preferable material for the contact-point connecting unit.

However, the present invention is not limited thereto. The contact-point connecting unit includes an electrically connecting layer 1 made of a thin film for electrical conduction, an insulating layer 2 and a thermally connecting layer 3 made of a metallic film for heat conduction.

Specifically, the contact-point connecting unit includes, at one side thereof, an electrically connecting layer 1, an insulating layer 2 and an thermally connecting layer 3, in which the electrically connecting layer and the thermally connecting layer are made of resilient material, while the contact-point connecting unit includes, at another side thereof, the electrically connecting layer 1 and the thermally connecting layer 3, in which the electrically connecting layer and the thermally connecting layer are alternatively arranged to form a"V"shape.

FIGs. 5 and 6 are graphs showing the maximum temperature differences among the laminates in the cases of using the heat conducting separator and the side heat-conducting unit shown in FIG. 2, the side heat-conducting unit and the direct heating separator shown in FIG. 3, and the conventional separator.

FIG. 7 is a schematic view illustrating heat flow during cooling process according to the present invention.

FIG. 8 is a schematic view illustrating an arrangement of laminates to be consolidated by using the apparatus shown in FIGs. 1 and 2. In FIG. 8A, reference numeral 1 denotes the side heat-conducting unit shown in FIG. 1, and reference numeral 2 denotes a carrier plate used for easily moving the stacked laminates to the press to heat and pressurize the stacked laminates.

The carrier plate has a channel 4 for fixing the side heat-conducting unit shown in FIG. 1.

Reference numeral 3 denotes books of the separators and laminates which are alternatively arranged on the carrier plate, and reference numeral 5 denotes the locking member for closely contacting the separators and laminates with the side heat-conducting unit 1. FIG. 8B shows a stack of books which are fixed on the carrier plate prior to moving to the press.

The process of cooling the consolidated laminates using the improved heat conducting system of the present invention will now be described.

After consolidating the laminates interposed between platens, cooling water is supplied to the platens above and below the laminates to cool the platens, thereby producing heat flow as shown in FIG. 6. According to the heat flow, the cooling speed between the laminates is varied depending upon positions of the laminates in the stack. As a result, the extent of stress generated due to different levels of the contracting/expanding rates between the metal separator and the consolidated laminate varies from laminate to laminate. Therefore, the dimensional instability of a laminate produced by a conventional method can be as high as 0.02% to 0.04%.

Upon using the heat conducting system of the present invention, the heat is transferred to the side heat-conducting unit through the separator, as well as the common heat transfer as shown in FIG.

7. The heat transferred through the side heat-conducting unit is rapidly transferred by the upper and lower platens and natural heat radiation. Since there is additional heat transfer from the consolidated laminates to the platens, the temperature variation among the laminates is improved, thereby decreasing the dimensional instability of the laminate to as low as 0. 003% to 0. 015%.

The high dimensional stability of the laminate which is obtained by the reduced temperature variation may improve yields of the interconnection.

The present embodiment is to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims.

Embodiment 1 : Manufacture of the conductive separator shown in FIG. 2 which has heat conducting layers Example 1-A : After obtaining a desired surface roughness on a surface of a common metal separator, a heat conducting layer having a thickness of 5 am to 2 mm was formed on the separator by electrolytic plating in a copper sulfate solution. Since copper is an easily oxidizable metal, the surface of the metal was plated with a noble metal, such as nickel, gold, chrome or the like, in a thickness of 1 to 50 microns, and pressurized in a press under a pressure of 100 to 10,000 PSI, thereby hardening the crystal structure of the plated metal.

Example 1-B: A separator was made of two stainless steel plates in a thickness of 0.5 mm to 3 mm First, a heat conducting layer is deposited on one stainless steel plate, and a heat conduction pattern is formed. Another stainless steel plate is bonded to the plate so that a heat conduction pattern is formed in order for the manufactured heat conducting plate to provide the pattern of the heat conduction therein.

Embodiment 2 Example 2-A: Lamination using the side heat-conducting unit shown in FIG. 1 and the conductive separator shown in FIG. 2 The example is to illustrate a detailed method of manufacturing a circuit board using side heat-conducting units shown in FIG. 1 and the conductive separators shown in FIG. 2. The side heat-conducting unit was made of bronze. Specifically, a pair of female and male bodies (1.0 cm x 1.8 cm x 2.0 cm) were prepared to have a proper shape in such a manner that a minimum height of the combined body is 1.2 cm and a maximum height thereof is 1.8 cm, in the case of

mounting the spring and applying pressure to the body (the dimensions are varied depending upon the capability of a press). The side heat-conducting unit was provided with the spring and a locking member, and was mounted to a carrier plate so that it can move along a plurality of chamlels.

In order to implement a lamination cooling experiment, a multilayer printed circuit board was manufactured by use of a side heat-conducting unit, a conductive separator and a vacuum press having the following processes: 1. Four side heat-conducting units disposed on the carrier plate were sufficiently spaced, and a cushion pad was placed between the side heat-conducting units on the carrier plate, wherein the conductive separator shown in FIG. 2 was disposed on the cushion pad.

2. A copper foil, bonding prepreg, a set or sets of an innerlayer circuit board were disposed on the conductive separator shown in FIG. 2, and then another conductive separator shown in FIG. 2 was disposed on the conductive separator.

3. Repeated step 2 multiple times.

4. After disposing the cushion pad on the conductive plate shown in FIG. 2, a top plate was laid on the cushion pad, and the side heat-conducting unit of FIG. 1 attached to the channel of the carrier plate was pressed to make close contact to the sides of conductive separators to achieve close contact with the heat conducting layers of the conductive separators.

5. The carrier plate was moved to the press, and was interposed between the platens.

The interior of the press was maintained in a vacuum state by closing a door.

6. After 5 minutes, the lower platen was moved upwardly to the upper platen to slowly increase the pressure to 5 to 1000 psi.

7. The temperature of the laminates was increased to 180°C in a ratio of 1.0 to 5°C per minute.

8. After the laminates were cured at a temperature of 170°C to 180°C for 100 minutes, a heating medium was turned off, and the cooling water was supplied to the upper and lower

platens.

9. When the temperature of the innermost laminates reached 80°C, the vacuum state was released by opening the door, and the carrier plate was drawn from the press through the door.

The locking member of the side heat-conducting units was released, and the conductive separators and the formed laminates were detached from each other, thereby manufacturing the printed circuit boards.

Example 2-B (Comparative Embodiment): Lamination using a conventional method A printed circuit board was prepared using the conventional method, without use of the cooling system of the present invention.

Example 2-C: Comparative Experiment 1) Test of temperature variation in the laminates Maximum temperature variations among the laminates during the cooling cycles of the present invention and the convention method were compared. The comparison was performed by use of a thermocouple. The results of the test are shown in the graph of FIG. 5.

As shown in the graph, the conventional cooling method shows the temperature variation of about 20°C at a temperature of 128°C, while the present invention shows the temperature variation of about 12°C. The conventional method shows the temperature variation of about 25°C at a temperature of 108°C, while the present invention shows the temperature variation of about 15°C. It can be understood that the cooling method of the present invention shows an improvement of 8°C in the temperature variation at the temperature of around 130°C and an improvement of about 10°C at around 118°C.

2) Test of dimensional stability Test of dimensional stability of the laminate was performed according to IPC TM450.

In the case of the laminate formed by the conventional method, the dimensional stability is 0.035%, while the dimensional stability of the present invention is 0.008%, so that the present invention shows improvement of about four times when compared to conventional dimensional

stability.

Embodiment 3 Manufacture of a direct heating separator shown in FIG. 3 The direct heating separator manufactured by the assignee was employed. A surface of an outmost insulator of the separator was dipped into a solution of sodium naphthalene for 5 minutes and then was cleaned. The area to form electrically contacting points of the separator was coated with a photoimagable dielectric resin. The remaining area of the electrically contacting points was plated with tin in a thickness of 0.1 to 5 p. m. Then, the separator was plated with electroless copper in a thickness of 0.1 to 5 jj, m. The tin was stripped with fluoroboric acid solution, and the portion from which the tin was removed was applied with a plating resist. The separator was formed with a heat conducting layer in a thickness of 10 to 100 Am. An anti-oxidizing layer was formed on the copper surface in a thickness of 1 to 25 um using a nickel sulfamate solution. After the plating resist was stripped off in a sodium hydroxide solution, cleaned, and dried, it was then pressed by a press to manufacture the direct heating separator.

Embodiment 4 Manufacture of the contact-point connecting unit shown in FIG. 4 Two sheets of beryllium-copper alloy were bonded with each other by a high heat- resistant silicon adhesive, except at the area portions to be used as a contact point. The unbonded portion was cut by use of a wire cutter, and the cut portions were alternatively bent in such as a manner that one side was connected to the heat conducting layer and the other side was connected to a circuit of the heating layer.

Embodiment 5 Example 5-A: Lamination using the side heat-conducting unit of FIG. 1, the direct heating separator of FIG. 3 and the contact-point connecting unit of FIG. 4 Manufacture of the multilayer printed circuit board of glass fiber reinforced epoxy

employing the present invention will now be described. A rectifier of 2, OOOA and 15V was used as a electrical source. The circuit board was manufactured by the following steps.

1. After disposing a cushion pad on a carrier plate, as described in Embodiment 1, a copper plate was disposed on the cushion pad, and the direct heating separator of FIG. 3 was disposed on the copper plate.

2. On the direct heating separator, copper foil, set (s) of bonding prepreg, and innerlayer circuit board, bonding prepreg, and copper foil were disposed in such a manner that the laminate was placed apart from a contacting portion by more than 3 cm.

3. After disposing the contact-point connecting unit of FIG. 4 on the contacting portion of the direct heating separator, the direct heating separator of FIG. 3 was disposed on the connecting unit.

4. Repeated steps 2 and 3 multiple times.

5. After disposing the contact-point connecting unit of FIG. 4 on the contact point of the separator, a copper plate having a thickness of 1.0 mm was disposed on the connecting unit, and the cushion pad was disposed on the copper plate leaving the electrical connecting area uncovered.

6. The side heat conducting unit of FIG. 1 was closely mounted to three sides of the laminate of FIG. 3 on which the connecting unit of FIG. 4 was not disposed.

7. The carrier plate was moved to the press, and was interposed between the platens to achieve electrical connection to the copper plates disposed on the laminate. The interior of the press was maintained in a vacuum state.

8. After 5 minutes, the lower platen was moved upwardly to slowly increase the pressure to 5 to 1000 psi.

9. After turning on the power, the temperature of the laminates was increased to 180°C in a ratio of 1.0 to 5°C per minute.

10. After the laminates were cured at 170°C to 180°C for 100 minutes, the electrical

power was turned off, and the cooling water was supplied to the upper and lower platens.

11. When the temperature of the innermost laminates reached 80°C, the vacuum state was released by opening the door, and the carrier plate was drawn from the press through the opened door. The conductive separator and the formed laminates were detached from each other, thereby manufacturing the printed circuit board.

Example 5-B (Comparative Embodiment): Lamination using a conventional method A printed circuit board was prepared through the conventional method of employing a stainless steel separator. Neither the side heat conducting unit nor the conductive separator of the present invention was used.

Example 5-C: Comparative Experiment 1) Test of temperature difference among the laminates A maximum temperature difference among the laminates in the case of the present invention and the conventional method were employed. The comparison was made by use of a thermocouple. The results of the tests are shown in the graph of FIG. 6.

As can be seen from the graph, the conventional method shows the maximum temperature difference of about 20°C at 128°C, while the method of the present invention shows the maximum temperature difference of about 15°C. The conventional method shows the maximum temperature difference of about 25°C at 108°C, while the method of the present invention shows the maximum temperature difference of about 20°C. The test results are to be understood that the present invention improves in the maximum temperature difference by about 5°C at 130°C and about 5°C at about 118°C.

2) Test of dimensional stability Test of dimensional stability of the laminate was performed according to IPC TM450.

In the case of the laminate formed by the conventional method, the dimensional stability is 0.035%, while the dimensional stability of the present invention is 0.015%. As a result, the present invention shows improvement in dimensional stability as much as four times over the

conventional method.

While the present invention has been described and illustrated herein with reference to the preferred embodiments thereof, it will be apparent to those skilled in the art that various modifications and variations can be made therein without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers all modifications and variations of this invention that come within the scope of the appended claims and their equivalents.

Industrial Applicability With the above description, in the manufacture of the printed circuit board of polymer composite, it is impossible in theory to produce articles without generating stresses due to the difference between the contracting/expanding rate of the separator and contracting/expanding rate of the polymer composite when cooling a consolidated board from a high temperature at cure cycle to'a low temperature for unload. However, with the improved thermal conducting system of the present invention, the temperature difference among the laminates is reduced. It is possible to minimize variation in the total amount of stress embedded in the cured and cooled laminates to create laminates with improved dimensional stability. In particular, in the case of using both the direct heating separator and the side heat conducting unit, the temperature variation may be controlled to the lowermost level during heating and cooling cycles, thereby producing a laminate having high dimensional stability.

In addition, the present invention has another advantage of performing the overall lamination processes, while maintaining the advantages of the conventional method.