JPH0575247A - Method of mounting chip - Google Patents

Abstract

PURPOSE:To provide a method of mounting a chip, in which the quantity of solder can be changed corresponding to the kind of the chip and no solder bridge and solder ball is produced. CONSTITUTION:The method of mounting a chip is composed of a process, in which the upper section of the circuit pattern 2 of a board 1 is coated with cream solder 3 prepared by mixing a high boiling-point solvent, a low- temperature activator and a high-temperature activator by a screen printer 11, a process, in which the board 1 is heated by a reflow device 21 and only the low-temperature activator is activated, a process, in which the chip P is stuck and mounted on heated solder by a chip mounting machine 31, and a process, in which the board 1 is heated at a high temperature by the reflow device 21, the high-temperature activator is activated and the electrode E of the chip P is fixed onto the circuit pattern 2 by solder 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chip mounting method, and more particularly, to change the amount of solder formed on a circuit pattern of a substrate according to the type of the chip while changing the electrodes of the chip to the circuit of the substrate. It relates to means for good adhesion on the pattern.

[0002]

2. Description of the Related Art The process of mounting chips such as ICs, LSIs, resistance chips, and capacitor chips on a substrate is a process of forming solder on the circuit pattern of the substrate, and a process of mounting chips on this solder by a chip mounting machine. , The solder is heat-treated by a reflow device to fix the electrodes of the chip on the circuit pattern.

As means for forming solder on the circuit pattern of the substrate, means for applying cream solder on the circuit pattern by a screen printing machine and means for forming solder on the circuit pattern by solder plating means or solder leveler means It is roughly divided into. The solder formed by the latter means is generally called a solder precoat.

[0004]

However, in the former, that is, the means for applying the cream solder onto the circuit pattern by the screen printing machine, the cream solder is crushed when the chip is mounted by the chip mounting machine, and the solder is reflowed by the reflow device. There is a problem that a solder bridge or a solder ball, which causes a short circuit of the circuit, is likely to be generated by the molten solder when the heat treatment is performed.

The latter, that is, the solder precoat means, has a problem that only a solder having a constant thickness can be formed regardless of the type of chip. That is, it is desirable to change the amount of solder depending on the type of chip, and in order to change the amount of solder, the thickness of solder must be changed. It has been extremely difficult in practice to change the thickness of the solder. In addition, since the solder precoat does not have flux, when mounting the chip, flux must be applied on the solder precoat to improve the wetting property of the solder, which causes a problem that the number of processes is increased and labor is required. It was

Therefore, it is an object of the present invention to provide a novel chip mounting means which can solve the problems of the above-mentioned conventional means.

[0007]

To this end, the present invention provides
(1) A step of applying a cream solder containing a high boiling point solvent, a low temperature activator and a high temperature activator on a circuit pattern of the board by a screen printing machine, and (2) heating the board by a reflow device. A step of activating only the low-temperature activator, and (3) a step of adhering and mounting a chip on the heated solder by a chip mounting machine,
(4) The substrate is heated by a reflow device at a temperature higher than that in the step (2) to activate the high temperature activator,
A chip mounting method is constituted by a step of fixing the electrodes of the chip on the circuit pattern by soldering.

[0008]

According to the above construction, the amount of solder on the circuit pattern can be adjusted by changing the size and shape of the pattern hole of the screen mask of the screen printing machine. Further, by mixing the low temperature activator and the high temperature activator, the wetting property of the solder in the two reflows before and after can be improved, and further by mixing the high boiling point solvent, the electrode of the chip is adhered to the solder, By performing the second reflow, the electrodes of the chip can be reliably fixed on the circuit pattern.

[0009]

Embodiments of the present invention will now be described with reference to the drawings.

1A to 1D show a chip mounting process. FIG. 1A shows a state in which the cream solder 3 is applied on the circuit pattern 2 of the substrate 1 by the screen printer 11. Reference numeral 12 is a squeegee, and 13 is a screen mask. Substrate 1 is screen mask 1
The cream solder 3 is applied onto the circuit pattern 2 through the pattern holes 14 by bringing the squeegee 12 into sliding contact with the lower surface of the circuit pattern 3. The amount of cream solder 3 applied is preferably changed according to the type of chip, but according to this means, the amount of cream solder 3 applied can be easily adjusted by changing the shape and size of the pattern hole 14. it can.

A low temperature activator, a high temperature activator, and a high boiling point solvent are mixed in the flux of the cream solder 3. The low-temperature activator is activated at a relatively low temperature (for example, 200 ° C. or lower) to improve the wetting property of the solder, and for example, aniline hydrochloride having a melting point of 192 ° C. can be used. High-temperature activators have high temperatures (for example, 220 ° C or higher)
Is used to improve the wetting property of the solder, and for example, diethylamine hydrochloride having a melting point of 226 ° C. can be used. Further, the high-boiling point solvent retains the adhesiveness even after the reflow, and has a function of attaching the chip to the solder as described later. As the high boiling point solvent, for example, dioctyl phthalate can be applied. Of course, the cream solder may be mixed with an improving agent other than the above.

FIG. 1B shows how the screen printing machine 11 applies the cream solder 3 and then performs the first reflow process. Reference numeral 21 is a reflow device, 22 is a conveyor for carrying the substrate 1, 23 is a heater,
24 is a fan and 25 is a heating chamber.

The reflow device 21 heats the substrate 1 to a temperature at which only the low temperature activator is activated and the high temperature activator is not activated. In this way, after the cream solder 3 is heat-treated at a temperature higher than the melting point of the solder powder and at a relatively low temperature,
When cooled, the solder 3 is solidified and a thin film of the flux a containing the high boiling point solvent is formed on the surface thereof. Figure 1 (b)
As shown in the partially enlarged view, the solder 3 solidified on the circuit pattern 2 is a solder precoat similar to solder plating or solder leveler. When the flux a or the surface of the solder precoat oxidizes, the wetting property deteriorates, so this reflow is preferably performed in a non-oxygen atmosphere such as nitrogen reflow or vapor phase reflow.

FIG. 1C shows a state in which the chip P is mounted on the solder 3 by the transfer head 32 of the chip mounter 31. Reference numeral 33 is a nozzle that adsorbs the chip P. The electrode E of the chip P lands on the solder 3, but since the flux a containing an adhesive high boiling point solvent adheres in a thin film on the solder 3, the electrode E of the chip P is solder 3 It is firmly adhered so that it will not be displaced on top.

FIG. 1D shows the second reflow process. The reflow device 21 heats the substrate 1 at a high temperature so that the high temperature activator is activated and preferably the high boiling point solvent in the flux a is vaporized. The second reflow is also preferably performed in a non-oxygen atmosphere in order to prevent deterioration of the solder 3.

FIG. 2 shows the substrate 1 on which the chip mounting is completed as described above. As shown in the figure, the solder 3 fixes the electrode E of the chip P on the circuit pattern 2 of the substrate 1 with good wetting due to the activation of the high temperature activator.

[0017]

As described above, according to the present invention, the electrodes of the chip can be reliably fixed on the circuit pattern of the substrate. Moreover, the amount of solder can be adjusted according to the type of chip, and the chip can be satisfactorily mounted on the substrate without the occurrence of solder bridges or solder balls that cause short circuits.

[Brief description of drawings]

FIG. 1 is a process diagram of mounting a chip according to the present invention.

FIG. 2 is a front view of a chip after mounting according to the present invention.

[Explanation of symbols]

 1 substrate 2 circuit pattern 3 cream solder 11 screen printer 21 reflow device 31 chip mounter

Claims (1)

[Claims] 1. A step of applying a cream solder containing a high boiling point solvent, a low temperature activator and a high temperature activator onto a circuit pattern of a substrate by a screen printer, and (2) reflowing the substrate. Heating by a device to activate only the low-temperature activator, (3) a step of mounting a chip on the heated solder by a chip mounting machine, and (4) reflowing the substrate. The device is heated at a higher temperature than the step (2) to activate the high temperature activator,
And a step of fixing the electrodes of the chip on the circuit pattern by soldering.