JP2001196730A - Method for forming bump of area array package - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming bumps of an area array package by a ball-mounting method corresponding to the trend of finer pitch of area array package, in order to solve the problem of bump forming method of area array package employing a conventional ball mounting method that the yield is low, because of small ball diameter due to the trend of finer pitch of area array package. SOLUTION: All mask openings of a masked tray are filled with solder balls, and a thermally stripping sheet is attached onto the arranged solder balls, thus transferring the solder balls to the thermally stripping sheet by adhesion. Subsequently, the masked tray is separated and the solder balls adhering fixedly to the thermally stripping sheet are mounted on the electrodes of an area array package, while being aligned therewith and then the solder balls are melted by heating through reflow thus forming bumps.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an area array package, and more particularly to a method of forming a bump on a substrate electrode of an area array package.

[0002]

2. Description of the Related Art A ball mounting method is known for forming bumps on electrodes of an area array package. A conventional bump forming method using a ball mounting method will be described with reference to FIG. In FIG. 2, 7 is an area array package, 8 is an electrode of the area array package, 10 is a mounter head, 11 is an array plate, 12 is a solder ball, and 13 is an inspection machine. First, the solder balls 12 are arranged on the mounting plate 1 of the mounter head 10.
Adsorb to 1. Next, the presence or absence of suction of the solder balls 12 is inspected by the inspection machine 13 to confirm that the solder balls 12 are adsorbed on all of the array plates 11, and then the electrodes 8 of the area array package 7 are aligned with the mounter head 10. Then, the solder balls 12 are transferred to the electrodes 8 of the area array package 7. Thereafter, the solder balls 12 are melted on the electrodes 8 of the area array package 7 by reflow heating to form bumps.

[0003]

However, as the pitch of the area array package becomes narrower, the diameter of the solder ball also becomes smaller, and a problem has arisen that the solder ball suction rate of the array plate is reduced. In addition, there has been a problem in that the solder balls float during preheating during reflow, and the solder balls overlap between adjacent ones to induce bridges and unsolder. The present invention has been made to solve the above problems, and has as its object to provide a method of forming a bump of an area array package corresponding to a narrow pitch.

[0004]

The bump forming method for an area array package according to the present invention comprises the following steps. a. A mask having an opening having the same arrangement as the electrode arrangement of the area array package is prepared in advance, and solder balls are filled in all mask openings of a masked tray provided with a bottom plate for receiving solder balls on the lower surface of the mask. Process. b. Attaching a heat-releasable sheet to the solder balls arranged in the mask opening. c. After the solder balls on the tray with the mask are adhesively transferred to the thermal release sheet with the adhesive of the thermal release sheet and the tray with the mask is separated, it is confirmed that all the solder balls are adhered to the thermal release sheet. The process of applying to the inspection machine. d. A step of positioning the solder balls adhered to the heat-releasable sheet on the electrodes of the area array package, placing the solder balls on the electrodes, and performing preheating by reflow to reduce the adhesive force of the pressure-sensitive adhesive of the heat-releasable sheet. e. A step of melting the solder balls by main heating in reflow and peeling the thermally peelable sheet from the solder balls to form bumps.

According to the bump forming method of the area array package of the present invention, even when the solder ball diameter is small in the narrow pitch area array package, the adhesive of the heat release sheet reliably captures and temporarily fixes the solder balls. There is no trouble in re-arranging the solder balls, and there is no bridge or unsolder due to the overlapping of the solder balls between adjacent ones due to the floating of the solder balls.

In the bump forming method for an area array package, a mask having an opening larger than the diameter of the solder ball and having a thickness smaller than the diameter of the solder ball, the opening being provided in the same array as the electrode array of the area array package; It is characterized in that a tray with a mask comprising a bottom plate provided in parallel with the mask on the lower surface of the mask is used so that the largest diameter portion comes into contact with the mask and the upper part of the solder ball comes out above the surface of the mask.

When the tray with the mask is used, the maximum diameter of the solder ball is held by the opening wall surface of the tray with the mask, so that the positional accuracy of the solder ball arrangement is high, and the upper part of the solder ball is placed on the mask surface. Since it comes out, the accuracy of capturing the solder ball by the heat release sheet is high.

[0008] In the bump forming method of the area array package, the solder balls are captured by using a heat release sheet whose adhesive strength is reduced by heating.

The heat-peelable sheet is an adhesive sheet that adheres to an adherend at room temperature in the same manner as a normal pressure-sensitive adhesive sheet, and when it is desired to peel it, the adhesive force is lost only by heating, and is suitable for temporarily fixing solder balls. As a product of the heat-peelable sheet, for example, there is “Riba Alpha” of Nitto Denko Corporation. When the heat-peelable sheet is used, the adhesive strength of the pressure-sensitive adhesive is reduced before the solder ball is melted, so that the peeling is easy without hindering the formation of the bump.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a flow of an embodiment of forming a bump by the ball mounting method of the present invention. In FIG. 1, 1 is a solder ball, 2 is a tray with a mask, 3 is a heat release sheet, 4 is an adhesive of the heat release sheet 3, 5 is a target mark, 6 is an inspection machine, 7 is an area array package, and 8 is an area. The electrodes 9 of the array package 7 represent bumps formed on the electrodes 8.

A mask having the same arrangement as the arrangement of the electrodes 8 of the area array package 7 is prepared in advance. The mask has good workability and can maintain flatness even if it is thin. For example, a mask can be machined with a drill or the like using a stainless steel plate. The opening diameter of the mask is larger than the solder ball diameter, and the thickness of the mask is smaller than the solder ball diameter.
A bottom plate for receiving a solder ball is attached to the lower surface of the mask to complete the tray 2 with the mask. If the gap between the mask and the bottom plate of the tray 2 with mask is set to the remaining half of the solder ball diameter minus the mask thickness, the solder ball maximum diameter is held at the center of the mask opening wall surface, and the solder ball is removed from the mask surface. As the upper part comes out, it is convenient.

First, the solder balls 1 are filled in all the openings of the masked tray 2. (FIG. 1A) Next, the heat release sheet 3 is attached on the solder balls 1 arranged in the mask opening. (FIG. 1 (b)) The heat release sheet 3 is previously processed to the same size as the area array package 7, and the adhesive 4 of the heat release sheet 3 has the same arrangement as the arrangement of the electrodes 8 of the area array package 7 and the solder ball diameter. It is preferable to apply it to the same size area as that described above. The target marks 5 are put on both the masked tray 2 and the heat-releasable sheet 3 so as to be convenient for the positioning at the time of the sticking.

The solder balls 1 on the mask-attached tray 2 are temporarily adhered to the heat-releasing sheet 3 by the adhesive 4 of the heat-releasing sheet 3, and the mask-attached tray 2 is separated.
Inspection machine 6 is used to confirm that all the solder balls 1 are adhered to the heat release sheet 3. (Figure 1
(C))

The solder balls 1 temporarily adhered and fixed to the heat-releasing sheet 3 are placed on the electrodes 8 of the area array package 7 in alignment. (FIG. 1 (d)) The target mark 5 is also attached to the area array package 7 so as to be convenient for alignment. By performing preheating by reflow in this state, the adhesive force of the adhesive 4 of the heat release sheet 3 is reduced.

The adhesive 4 loses its adhesive force by the main heating of the reflow, so that the solder balls 1 are easily separated and the bumps 9 are formed. (FIG. 1 (e)) Note that the temperature at which the pressure-sensitive adhesive 4 is peeled off is approximately 150 degrees Celsius, which is slightly lower than 200 degrees Celsius, which is the melting temperature of the solder.

[0016]

According to the present invention, since the pressure-sensitive adhesive surely captures and temporarily fixes the solder balls, there is no need for re-arranging the solder balls. Also, since the solder ball position is held until the solder starts melting by reflow,
There is no problem that the solder balls float and the solder balls overlap between adjacent ones to induce a bridge or unsolder, and the bump arrangement position accuracy after bump formation is extremely high.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a flow of an embodiment of forming a bump by a ball mounting method of the present invention.

FIG. 2 is a schematic view showing a flow of a conventional bump forming method using a ball mounting method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solder ball 2 Tray with mask 3 Thermal peeling sheet 4 Adhesive 5 Target mark 6 Inspection machine 7 Area array package 8 Electrode 9 Bump 10 Mounter head 11 Array plate 12 Solder ball 13 Inspection machine 14 Reflow heating

Claims (3)

[Claims] 1. A method for forming a bump of an area array package, comprising the following steps. a. A mask having an opening having the same arrangement as the electrode arrangement of the area array package is prepared in advance, and solder balls are filled in all mask openings of a masked tray provided with a bottom plate for receiving solder balls on the lower surface of the mask. Process. b. Attaching a heat-releasable sheet to the solder balls arranged in the mask opening. c. After the solder balls on the tray with the mask are adhesively transferred to the thermal release sheet with the adhesive of the thermal release sheet and the tray with the mask is separated, it is confirmed that all the solder balls are adhered to the thermal release sheet. The process of applying to the inspection machine. d. A step of positioning the solder balls adhered to the heat-releasable sheet on the electrodes of the area array package, placing the solder balls on the electrodes, and performing preheating by reflow to reduce the adhesive force of the pressure-sensitive adhesive of the heat-releasable sheet. e. A step of melting the solder balls by main heating in reflow and peeling the thermally peelable sheet from the solder balls to form bumps. 2. A mask having an opening larger than the diameter of the solder ball and having a thickness smaller than the diameter of the solder ball, the opening being provided in the same arrangement as the electrode array of the area array package, and the largest diameter portion of the solder ball contacting the mask. 2. The area array package according to claim 1, wherein a mask-equipped tray including a bottom plate provided in parallel with the mask is used on a lower surface of the mask so that an upper portion of the solder ball is above the mask surface. Bump forming method. 3. The method for forming a bump of an area array package according to claim 1, wherein the solder balls are captured using a thermal release sheet whose adhesive strength is reduced by heating.