JPH11111904A - Manufacture of solder printed board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the manufacture of a solder printed board, by which solder adheres onto the board accurately by planned quantity and which can surely prevent the problems of various printing troubles, such as paste sagging or oozing of solder paste remaining on the conventional board, or short circuit caused by the so-called bridge phenomena, or the like. SOLUTION: A screen 28 for printing is fixed on a board 22, with a through- hole of the screen 28 for printing registered in the specified position on the board 22, and a through-hole of the screen 28 for printing is charged by screen printing method with solder paste 29 which can be transformed from paste condition into fused condition by reflow heating, and the solder paste 29 is reflow-heated, with the screen 28 for printing kept fixed onto the board 22, whereby it is transformed from a paste condition into a fused condition, and the fused solder is cooled and transformed into a solid condition, and the screen 28 for printing is made to be peeled off from above the board 22.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a BGA (B
Like a relay board used for mounting electronic components that are not directly mounted on a mother board, such as chip electronic components such as LSIs, and mounting them on the mother board, such as a board of an all grid array (package). More particularly, the present invention relates to a method of manufacturing a solder printed board, which is manufactured by attaching a solder paste on the board by a screen printing method.

[0002]

2. Description of the Related Art As a conventional method for manufacturing a solder printed board, for example, there is a method shown in FIGS. That is, as shown in FIG. 7, a BGA package B shown in FIG. 7 has a relay board 52 on which a semiconductor element 50 covered with a mold resin 51 on one surface is mounted, and a relay board 52 shown in FIG. 9 is completed by providing a plurality of solder balls 55 electrically and vertically connected to the semiconductor element 50 through bonding wires 53 and conductor leads 54, as shown in FIG. Is what you do.

In order to provide a plurality of solder balls 55 on such a relay board 52 of the BGA package B, a method as shown in FIG. 10 is conventionally used. That is, as shown in FIG. 10A, the semiconductor element 50 in which one surface of the relay substrate 52 is coated with the mold resin 51 in advance,
The bonding wire 53, the conductor lead 54 and the like are mounted.

[0004] On the other surface of the relay board 52, FIG.
0 (b), a printing screen 5 having a plurality of through holes 57 formed at positions where a plurality of solder balls 55 are to be formed.
8 is positioned and fixed, and toothpaste-like solder paste 59 is pressed into the through-holes 57 by a screen printing method while applying rolling pressure by a rolling roller, and the solder paste 59 is relayed by its adhesive force. It is temporarily fixed on the substrate 52.

Then, the printing screen 58 is connected to the relay board 5.
By removing the solder paste mass 2 from the solder paste mass 60 before reflow as shown in FIG.
Are fixedly formed on the surface of the relay board 52.

[0006] Thereafter, as shown in FIG. 10 (d), the solder paste mass 60
Is heated to reflow, that is, the solder paste mass 60 is changed from a paste state to a molten state by heating to form a substantially hemispherical shape, and the shaped solder ball 55 is welded to the surface of the relay board 52. Thus, the BGA package B can be completed.

[0007]

However, in the above-described conventional method for manufacturing a solder printed board, when the printing screen 58 is peeled off from the relay board 52 after the solder paste 59 is printed, the solder printed board is not covered with the relay board 52. Although the amount of the solder paste mass 60 remaining on the printing screen 58 must be uniform at each position, a part of the solder paste 59 is attached to the side wall surface of the through-hole 57 of the printing screen 58 and is taken. 1
As shown in FIG. 1 (a), the amounts of the solder paste chunks 60 are different and non-uniform at each position. In other words, the amount of the solder paste mass 60 remaining at each position is different from the predetermined amount. There was a problem that it would change.

Further, as shown in FIG. 11B, the solder paste mass 60 remaining on the relay board 52 is dripped and becomes irregular, or as shown in FIG. 11D, or a small amount of solder paste clumps 60 adhere to the relay board 52 due to clogging of the through holes 57 of the printing screen 58 as shown in FIG. There is a problem that printing failure occurs.

Further, as described above, the amount of the solder paste mass 60 remaining on the relay board 52 differs at each position and becomes uneven, so that the solder paste mass 60 is melted by heating for reflow. In this case, as shown in FIG. 12, a bridging phenomenon may occur in which the adjacent solder paste masses 60 stick together. Then, there is a problem that a short-circuit (short-circuit) occurs between terminals that should not be energized during power supply.

Accordingly, the present invention has been made in view of the above problems, and has been described in view of the fact that the solder is accurately attached to a substrate by a predetermined amount,
It is an object of the present invention to provide a method of manufacturing a solder printed board that can reliably prevent various printing defects such as the dripping, bleeding, and insufficient amount of solder paste remaining on the board, or a short circuit due to a so-called bridge phenomenon. It is assumed that.

[0011]

In order to solve the above-mentioned problems, a method of manufacturing a solder printed board according to the present invention comprises aligning a through hole of a printed screen with a predetermined position on the board, and mounting the printed screen. It was fixed on the substrate, and solder paste capable of changing its state from a paste state to a molten state by reflow heating was filled into the through-hole of the printing screen by a screen printing method, and the printing screen was fixed on the substrate. Reflow heating the solder paste as it is to change the state from the paste state to the molten state, cooling the molten solder to change the state to a solid state, and peeling the printing screen from the substrate. It is what it was.

According to such a method of manufacturing a solder printed board, the solder paste is reflow-heated while the printing screen is fixed on the board to change the state from the paste state to the molten state. Is cooled to change the state to a solid state, and then the printing screen is peeled off from the substrate, so that the solder paste in the through-hole of the printing screen solidifies integrally, so that the solder is transferred to the female mold in the through-hole. It can be formed in a male shape almost identical to the shape.

[0013]

Embodiments of the present invention will be specifically described below with reference to the drawings. 1 to 6
Is a BGA (Ball Grid Array) according to the first embodiment of the method for manufacturing a solder printed board according to the present invention.
y) A diagram referred to for explaining the manufacturing method of the package A.

In FIG. 1, a BGA package A has a relay board 22 (substrate) in which a semiconductor element 20, bonding wires 23 and conductor leads 24 are mounted on one (lower side in the figure) surface and these are covered with a mold resin 21. have. Such a BGA package A is provided with the relay board 2
This is completed by providing a plurality of solder balls electrically connected to the semiconductor element 20 via the bonding wires 23 and the conductor leads 24 on the other (upper side in the figure) surface of the second.

In such a BGA package A, the solder balls are melted by reflow heating, and
2 can be mounted on a mother board by connecting it to a printed pattern on a mother board (PWB, printed wire board). The mounting can be performed by a chip component automatic mounting machine. What is a chip component?
For example, electronic components such as resistors and capacitors.

Hereinafter, a method for providing a plurality of solder balls on the relay board 22 of the BGA package A will be described. First, as shown in FIG. 2, a plurality of solders are provided on the other surface of the relay substrate 22 on which the semiconductor element 20, the bonding wires 23, the conductor leads 24, etc. A printing screen 28 having a plurality of through holes 27 is positioned at a position where a ball is to be formed, and the printing screen 28 is fixed to the relay board 22 by means (not shown).

The printing screen 28 used at this time is made of stainless steel. The method of forming the through-holes 27 is not to use an etching method in which the through-holes 27 are opened by corrosion with an etching solution, but by plating. 2
An additive method of forming an opening 7 is used.

Next, as shown in FIG. 3, a toothpaste-like solder paste 29 is pressed into each through hole 27 of the printing screen 28 by a screen printing method while applying rolling pressure by a rolling roller 32. Fill.

Next, the rolling roller 32 and the remaining solder paste 29 are removed from above the printing screen 28. As shown in FIG. 4, the printing screen 28 is fixed on the relay board 22 as it is. In this state, the solder paste 29 is applied to the printing screen 28 and the BGA
Reflow heating is performed together with the package A. Then, the state of the solder paste 29 changes from the toothpaste state to the molten state of the solder.

Since the printing screen 28 is made of stainless steel, the reflow heating temperature is set to 150.
The shape and size of the through-holes 27 do not change even when the temperature reaches about 220 ° C. to 220 ° C., and thus there is no problem in terms of heat resistance. In addition, since a heat-resistant adhesive is also used for a connection between the printing frame 28 and a support frame that supports the printing screen 28, there is no problem in terms of heat resistance at this connection.

Next, the printing screen 28 is connected to the relay board 2.
If the molten solder is cooled without being peeled off from above, the solder changes from a molten state to a solid state. Then, when the printing screen 28 is peeled off from the relay board 22, the solder balls 25 remain on the relay board 22 as shown in FIG.

Since the through-holes 27 of the printing screen 28 are formed by the additive method as described above, there is no burr unlike the through-holes by the etching method, and the opening of the through-hole 27 is smooth. Therefore, the through-hole 27 of the printing screen 28 can be easily separated from the solder ball 25 (plate separation).

Also, by using the stainless steel printing screen 28 as described above, the upper and lower surfaces of the printing screen 28 and the opening thereof are provided with the solder in the surface layer of the base material to be soldered. Since a so-called alloy layer formed by diffusion of tin (Sn) therein cannot be formed, the printing screen 28 can easily be detached from the solder ball 25 after reflow heating from this point.

Further, the conventional solder paste mass 60 in a raw paste state cannot withstand long-term storage, whereas the solder ball 25 of the BGA package A according to the embodiment of the present invention is in a solid state, so that long-term storage is possible. Can withstand. For this reason, it is possible to eliminate waste of waiting for the next process in so-called multi-production.

That is, for example, a first step of performing screen printing, a second step of using a high-speed automatic mounting machine for automatically mounting chip components, a QFP (Quad Flat)
package) or SOP (Small Outlin)
e package), a third step performed by using a low-speed automatic mounting machine that automatically mounts lead components, a fourth step of performing reflow heating by a reflow furnace, and the like. It takes 45 seconds,
Assuming that the time required for the second step is 60 seconds and the time required for the third step is 120 seconds, the time required for the third step is twice as long as the time required for the second step. There is a waste of waiting time.

Therefore, the above-described first to fourth steps are not performed in order, and the respective steps are performed individually and in an appropriate order, thereby preventing the wasteful time waiting for the next step. Although a multi-production method is conceivable, according to the method for manufacturing a solder printed board of the present invention, the solder balls 25 can withstand long-term storage as in the BGA package A of the above embodiment. It can greatly contribute to realization.

When the BGA package A is mounted on the mother board, reflow heating is performed again. At this time, a flux is applied to the solder balls 25 to remove impurities and connect the mother balls to the solder balls 25. The connectivity with the printed pattern of the substrate can be improved.

The flux includes activated flux, non-activated flux, water-soluble flux, organic acid flux, inorganic flux, etc., and is mixed with a solder paste or soldered by reflow heating as described above. Sometimes, it is used by applying flux to solder balls.

The solder balls 25 adhered to the relay board 22 as described above are connected to the through holes 27 of the printing screen 28.
Since it is completely solidified in the inside, as shown in FIG.
The solder balls 25 can be formed in a male shape almost completely the same as the female shape in the through-hole 27 of the printing screen 28, with the corners and the peripheral portion remaining almost intact.

For this reason, the solder adheres accurately to the substrate by a predetermined amount, and various printing defects such as dripping, bleeding, and insufficient amount of solder paste remaining on the substrate as in the related art, or a so-called bridge phenomenon. The problem such as a short circuit due to the above can be surely prevented.

As described above, since the solder can be accurately adhered on the substrate by a predetermined amount, it is possible to perform screen printing of a fine pitch (ultra fine pitch) and fine size print pattern.

In the above embodiment, the solder balls 25
Although the BGA package having the same shape and size has been described, the present invention can also be applied to substrates other than the BGA package in which the shape and size of the solder balls 25 are not the same.

In the above-described embodiment, the case where stainless steel is used for the printing screen 28 has been described. However, any other heat-resistant material, such as a polyimide material, whose dimensions and shapes do not change by reflow heating, can be used. Any material may be used.

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various other modifications may be made based on the technical concept of the present invention. Can be changed.

[0035]

As described above, according to the present invention,
Since the solder paste in the through-hole of the printing screen solidifies in one piece, the solder is formed in a male shape that is almost completely the same as the female shape in the through-hole. In addition to accurately adhering to the substrate, it is possible to reliably prevent various printing defects such as dripping of solder paste remaining on the substrate, bleeding and insufficient amount, or shorts due to a so-called bridge phenomenon. it can.

[Brief description of the drawings]

FIG. 1 is a view showing a BGA package A according to a first embodiment of a method for manufacturing a solder printed board according to the present invention;
FIG. 1A is a partial cross-sectional side view, and FIG. 1B is a perspective view.

FIG. 2 is a partial cross-sectional side view showing one step of a method for manufacturing a BGA package A.

FIG. 3 is a partial cross-sectional side view showing one step of a method of manufacturing the BGA package A.

FIG. 4 is a partial cross-sectional side view illustrating one step of a method of manufacturing the BGA package A.

FIG. 5 is a diagram showing a completed BGA package A;
FIG. 5A is a partial cross-sectional side view, and FIG.
FIG. 4 is a top view of the BGA package A shown in FIG.

FIG. 6 is a view showing individual solder balls 25;
6A is a side view thereof, and FIG. 6B is a top view thereof.

FIG. 7 is a perspective view of a conventional BGA package B viewed from a semiconductor element 50 side.

FIG. 8 is a perspective view of a conventional BGA package B viewed from a solder ball 55 side.

FIG. 9 is a partial cross-sectional side view showing a conventional BGA package B.

10A to 10C show a method of forming a solder ball 55 on a relay board 52 of a conventional BGA package B.
It is a partial section side view shown in order of (d).

FIG. 11 is a view showing a solder paste mass 60 formed on a relay board 52 of a conventional BGA package B;
11A is a side view of the solder paste mass 60 whose size is not uniform due to printing failure, and FIGS. 11B to 11D are top views of the solder paste mass 60 related to various printing defects.

FIG. 12 is a top view of a plurality of solder paste chunks 60 partially having a bridge phenomenon due to printing failure.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 20 ... Semiconductor element, 21 ... Mold resin, 22 ... Relay board, 23 ... Bonding wire, 24 ... Conductor lead, 2
5 solder balls, 27 through holes, 28 printing screens, 29 solder paste, 32 rolling rollers, 50
Semiconductor element, 51: molding resin, 52: relay board, 5
3: bonding wire, 54: conductor lead, 55: solder ball, 57: through hole, 58: printing screen, 59
... solder paste, 60 ... solder paste mass

Claims (3)

[Claims] A printing screen is fixed on the substrate by aligning a through hole of the printing screen with a predetermined position on the substrate, and a solder paste capable of changing its state from a paste state to a molten state by reflow heating. Filling the through holes of the printing screen by a screen printing method, reflow heating the solder paste while fixing the printing screen on the substrate to change the state from the paste state to the molten state, Cooling the solder in the molten state while being fixed on the substrate to change the state to a solid state, and peeling the printing screen from the substrate when the state of the solder changes to the solid state. Manufacturing method of printed circuit board. 2. The method according to claim 1, wherein the printing screen is formed of stainless steel. 3. The method according to claim 1, wherein the through holes of the printing screen are formed smoothly by an additive method by plating.