JPH0197643A - Correction of warp of printed circuit board - Google Patents

Abstract

PURPOSE:To prevent the disconnection of circuits due to uncontrolled force, by heating a printed circuit board whose substrate is a resin laminated plate to a temperature above the glass transition point of resin, and by cooling the board as corrected in warp on a flat face down to a temperature below the glass transition point. CONSTITUTION:A printed circuit board whose substrate is formed out of a resin laminated plate are heated to a temperature above the glass transition point of resin. In the case of epoxy resin, the temperature is set at over 120-150 deg.C. It is almost the same in the case of phenol resin. The printed circuit board is pressed by the flat face of a metal plate of aluminium or stainless with high flatness for correction of warp into a flat condition, and cooling is started at the same time with pressing to allow the printed circuit board to cool down to below the glass transition point. As the above process, warp correction does not require bending of the wiring board and permits no break of circuits.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field 1] The present invention relates to a method for correcting warpage of a printed wiring board using a resin laminate as a substrate.

[Background technology] Printed wiring boards undergo heating, humidification,
Due to various external influences such as pressurization, warpage occurs to a greater or lesser extent. However, in the past, mounting on printed wiring boards was done using leads, so warping of printed wiring boards did not pose much of a problem, but as surface mounting increases, warping of printed wiring boards has become a major problem. I'm dead.

For this reason, various studies have been made to correct the warpage of printed wiring boards, but the current practice is to correct the warpage by applying force to manually bend the printed wiring board in the direction opposite to the warpage. However, with this method, the warp tends to return to its original state and cannot reliably correct the warp.
Furthermore, since a bending force is applied to the printed wiring board, excessive force is applied to the circuits of the printed wiring board, which may lead to breakage or other damage.

``Object of the Invention 1 The present invention has been made in view of the above points, and provides a method for correcting warpage of a printed wiring board that can reliably correct the warpage (which may cause damage to the circuit). The purpose is to provide the following.

[Disclosure of the Invention] According to the present invention, in order to correct the warpage of a printed wiring board having a resin laminate as a substrate, the printed wiring board is heated to a temperature higher than the positive transition point of the resin of the board, and then the printed wiring board is heated on a flat surface. This method is characterized by pressing the printed wiring board to straighten the warp and then cooling it to a temperature below the positive transition point, and by heating it above the positive transition point of the resin of the board to straighten the warp to a 7-rat surface. By doing so, it is possible to correct the warp without applying excessive force and without fear of the warp returning,
The present invention will be explained in detail below.

The printed wiring board to be corrected in the present invention has a substrate formed of a resin laminate.

In other words, epoxy resin or 7
A prepreg is created by impregnating and drying a varnish of a thermosetting resin such as an enol resin, and this multiple prepreg and t! A metal foil-clad laminate can be created by stacking metal foils such as 4M and forming them under heat and pressure.Furthermore, the metal foil of this metal foil-clad laminate can be etched or made with holes. By doing so, a printed wiring board having a resin laminate as a substrate can be obtained.

To correct the warpage of the printed wiring board, the printed wiring board is first heated to a temperature equal to or higher than the glass transition point of the resin of the board. When the resin constituting the resin laminate is an epoxy resin, the positive transition point is 120 to 15
Since the temperature is 0°C, the printed wiring board is heated to a temperature higher than this temperature. The same applies to the case of the 7-el resin.

Although the upper limit of the heating temperature is not particularly set, it is necessary to adjust the heating temperature within a temperature range in which the resin does not undergo decomposition or other changes in quality. Further, the heating time when heating to a temperature equal to or higher than the positive transition point is preferably about 10 to 300 seconds, for example, in the case of a printed wiring board having a thickness of 1.61 mm. After the printed wiring board is heated to a temperature above the positive transition point in this manner, the printed wiring board is pressed with a seven-rat surface to make it into a flat state with no warpage. By heating the printed wiring board to a temperature below the glass transition point of the resin, it is possible to correct the warpage while removing residual stress in the printed wiring board. As the flat surface that corrects the warpage of the printed wiring board into a flat state, metal plates such as aluminum and stainless steel having excellent flat surfaces, resin plates such as Teflon-coated engineering plastics, etc. can be used. By sandwiching the printed wiring board between these plates and applying pressure, it is possible to correct the warpage of the printed wiring board along the 7 rat surfaces of the plates.

For example, it is sufficient to apply a pressure of 5 to 100 kg to a printed wiring board with a size of 30 em x 50 cm.

In this way, when pressing the printed wiring board with the 7 rat surface, cooling is started at the same time, the temperature of the printed wiring board is lowered to below the glass transition point, and the next process can be carried out.
Lower the temperature to about ℃. At this time, an appropriate temperature lowering time is about 8 to 180 seconds. In this way, the printed wiring board is fixed in the unwarped state by cooling it to a temperature below the glass transition point after the warpage has been corrected, and the warpage is corrected without causing the warp to return. This is possible. In this way, for example 25
0ma+X 300mm size printed wiring board 1
．． It is possible to correct a warpage of 0 nua to 0.1 mm or less. Further, the printed wiring board can be cooled by using a plate that holds the printed wiring board in place to correct warpage and also functions as a cooling plate. If this board is a metal plate, the printed wiring board can be cooled by absorbing the heat of the printed wiring board and dissipating the heat, and a coolant can be forced to flow inside the board to perform a forced cooling effect. You can also

Of course, cooling can also be performed by immersing the device in cooling water. In addition, through the above heating and cooling,
Ideally, there should be no temperature difference between each part of the printed wiring board or between the front and back sides, but in reality, the temperature difference between each part is 5°C.
The temperature difference between the front and back surfaces is preferably within 3°C.

Next, an example of the apparatus used in the present invention will be explained based on the drawings. The device has a loading section 10 at the front, an unloading section 11 at the rear, and a heating section 12 at the center. A furnace 13 is provided. There are entrances and exits at the front and rear of the heating furnace 13, as shown in Figure gi (a) and Figure 1 (b).
As shown in the figure, the front shutter 14 and the rear shutter 15
Each one can be opened and closed. Also, a conveyor 16 formed by a par chain conveyor runs from the loading section 10 through the heating furnace 13 to the unloading section 11.
is the provision. As shown in FIG. 2, along the upper side of this conveyor 16, several (for example, 11) pieces of itopers 17 are disposed parallel to the conveyor 16 and fixed to a conveyor frame 18 or the like.

Each ID par 17 is divided into an ID bar 17a on the carry-in side provided in the carry-in section 10, an ID bar 17b on the inside of the heating furnace provided in the heating furnace 13, and an ID bar 17c on the carry-out side provided in the carry-out section 11. In addition, the loading side is the ID bar 17a.
The interior of the heating furnace and the inner bar 17b may be integrally continuous.

In addition, inside the heating furnace is the idle bar 17b and the unloading guide bar 17.
A pressurizing device (i!1
9 is the setting. The pressurizing device 19 is formed by several (for example, 11) pressurizing cooling plates 20 such as aluminum plates whose front and back sides are polished to smooth planes, and one end of each pressurizing cooling plate 20 is Fixed pressurized cooling plate 2
0a, and the other is a movable pressurized cooling plate 20b.

The fixed pressurized cooling plate 20a of each pressurized cooling plate 20 is fixed on the carrying-out section 11, and as shown in FIG. Each movable pressurized cooling plate 20b is slidably passed through the protruding rod 21 and suspended, and a connecting device 22 such as a chain or wire is connected between each pressurized cooling plate 20.
For example, each pressurized cooling plate 20 is connected to 20a.
The length of the connector 22 is set so that the thickness of the connector 22 is 111 mm, and the distance between each pressurized cooling plate 20 is 7 mm at the maximum. As shown in FIG. 2, the tip of the rod 24 of the air cylinder 23 is connected to the movable pressurized cooling plate 20b located at the end opposite to the fixed pressurized cooling plate 20a.
By operating the sill 23 and protruding the rod 24, each movable pressurized cooling plate 20b is pressed down in turn,
Conversely, by drawing the rod 24 into the sill 23, each movable pressurized cooling plate 20b can be sequentially separated by the action of the connector 22.

Therefore, the printed wiring board A is transported to the conveyor 1 of the GIO.
Each guide bar 17a is supplied on top of the conveyor 16, and is fed into the heating furnace 13 as the conveyor 16 is driven in a standing state supported by each guide bar 17a. - The conveyor 16 is driven to run with the printed wiring boards A held upright by the guide bar 17a so that a large number of printed wiring boards A (for example, 10 sheets) can be fed into the heating furnace 13 and heated at a time. Inside the furnace 13, each printed wiring board A is supported by a guide bar 17b and maintained in an upright state, and is heated in this state.

Since there is a guide bar 17b between each printed wiring board A, a gap is created between each printed wiring board A, and heat is distributed uniformly over the entire surface of each printed wiring board A, and the printed wiring board A is uniformly distributed. It can be heated to. The conveyor 16 is operated intermittently at predetermined time intervals, and when several sets of printed wiring boards A are sequentially introduced into the heating furnace 13, the first printed wiring board A undergoes a positive transition of the resin of the board. It is heated to a higher temperature than the point, and as the conveyor 16 is driven, it comes out from the heating furnace 12 to the discharge ff511.

Each printed wiring board A that has come out to the unloading section 11 in this way is inserted and set between each pressurized cooling plate 20 arranged corresponding to the rear end of each guide bar 17b. Then, the cylinder 23 is actuated, the rod 24 protrudes, and the movable pressurized cooling plates 20a are sequentially slid and pressed toward the fixed pressurized cooling plate 20b, and the printed wiring board A is moved between the pressurized cooling plates 20. Pressure is applied to the printed surface of the pressurized cooling plate 20 to correct the warpage. In addition, by bringing the pressurized cooling plate 20 into contact with the printed wiring board A in this way, the heat of the printed wiring board A is absorbed and radiated, and each printed wiring board A is kept from a temperature below the glass transition point. Further, it is possible to cool the printed wiring board A to a temperature of 50 to 60°C at which it can be handled. Thereafter, the cylinder 23 is operated again to draw the rod 24 into the cylinder 23, and each movable pressurized cooling plate 20b is sequentially separated by the action of the coupling member 22 to return to its original state. and conveyor 16
Each printed wiring board A between the pressurized cooling plates 20
is moved from between the pressurized cooling plates 20 to between the ID pars 17c and carried out, and the next set of printed wiring boards A coming out of the heating furnace 13 is inserted between the pressurized cooling plates 20 and set. . Thereafter, in the same manner, the printed wiring boards A sequentially carried into the carrying-in section 10 are heated in the heating furnace 13 and cooled under pressure by the pressurizing device 19, and can be carried out from the carrying-out section 11 in a state in which the warpage is corrected. .

The invention will now be illustrated by examples.

As a K1 Takumi printed wiring board, an epoxy resin laminate with a lath cloth base and a copper-clad double-sided board with a size of 350 mm x 300 m+a and a thickness of 1.6 ITll11 was used. The epoxy resin of this printed wiring board had a positive transition point of 140' (:), and the warpage dimension was 1.0 m+a.
The temperature was raised to 0° C., and the sample was immediately sandwiched between two stainless steel plates with a smooth surface, and a force of 50 kg was applied to pressurize the sample. After one minute had passed while the pressure was being maintained, the temperature of the printed wiring board had dropped to 50°C, so the printed wiring board was taken out from between the stainless steel plates. When the warp of the printed wiring board was measured immediately after being taken out, the warp dimension was 0.1 ms+. Further, after this printed wiring board was left at room temperature for 24 hours, the warp was measured again, and the warp dimension was 0.1 mm, with no change.

Rusanko I A warpage correction test was conducted in the same manner as in the example except that the temperature at which the printed wiring board was heated was set at 120°C. In this case, the warp dimension of the printed wiring board immediately after being taken out from the stainless steel plate was 0°31. Further, when this printed wiring board was left at room temperature for 24 hours and the warpage was measured again, the warpage was 0.5 mm and showed a tendency to warp back.

[Effect of the invention 1 As described above, in the present invention, after heating the printed wiring board to a temperature higher than the positive transition point of the resin of the board, the printed wiring board is pressed against the printed surface to straighten the warp. By cooling the board to a temperature below the glass transition point, it is possible to unwarp the board by heating it above the plus transition point and removing residual stress, and by cooling the printed wiring board to a temperature below the glass transition point. Fix it in the unwarped state,
This allows the warp to be reliably corrected without causing the warp to return. Moreover, the warping can be done by pressing the printed wiring board against the printed surface, so there is no need to bend the printed wiring board, and there is no risk of damaging the circuits installed on the printed wiring board. There is no such thing.

[Brief explanation of the drawing]

FIGS. 1(a) and (b) are front and rear perspective views of an example of the device used in the present invention, FIG. 2 is an exploded perspective view of a portion of the same device, and FIG. FIG. 2 is a perspective view of a part of the above device. 13 is a heating furnace, 16 is a conveyor, 17 is an idle bar, 1
9 is a pressurizing device.

Claims (1)

[Claims] (1) To correct the warpage of a printed wiring board using a resin laminate as a substrate, heat the printed wiring board to a temperature higher than the glass transition point of the resin on the board, and then press the printed wiring board with a flat surface to correct the warpage. A method for straightening warpage of a printed wiring board, characterized by cooling the straightened state to a temperature below the glass transition point.