JP2019186259A - Manufacturing method of printed wiring board - Google Patents

Abstract

To improve solder ball mounting accuracy on a printed wiring board with a cavity.SOLUTION: A manufacturing method of a printed wiring board comprises: a step of preparing a printed wiring board 10 in which a cavity 12 is formed on a first main surface 10A and a connection pad 28 is exposed on the bottom surface of the cavity 12; a step of forming a flux layer 30 on the connection pad 28; a step of arranging a ball mounting mask 32 having an opening 32a at a position corresponding to the connection pad 28 and having a flat bottom surface 32d facing the first main surface 10A above the first main surface 10A; and a step of placing a solder ball B on the connection pad 28 through the opening 32a of the ball mounting mask 32 with the flux layer 30 interposed therebetween.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a method for manufacturing a printed wiring board, and more particularly to a method for manufacturing a printed wiring board on which solder balls are mounted by a ball mounting method.

  Patent Document 1 discloses a solder ball mounting method. As shown in FIG. 6, a plurality of connection pads 22 ′ on which solder balls B are mounted are formed on the upper surface of the printed wiring board 10 ′. The mounting of the solder ball B is performed using a ball mounting mask 32 'in which a plurality of openings 32a' corresponding to the connection pads 22 'are formed. In order to form a gap between the connection pad 22 ′ of the printed wiring board 10 ′ and the mask 32 ′, a recess 32 r ′ is formed on the lower surface of the mask 32 ′.

JP2015-12056A

  FIG. 7 shows a printed wiring board 10 ″ with a cavity in which a cavity 12 ″ is formed on the first main surface 10A ″ and the connection pad 28 ″ is exposed on the bottom surface of the cavity 12 ″. When the solder ball B is dropped and mounted on the connection pad 28 '' exposed in the cavity 12 '' using the conventional mask 32 'as described above, the connection pad in the cavity 12' 'from the mask 32'. Since the distance up to 28 ″ is large, the position of the solder ball B is shifted during dropping, and the mounting accuracy of the solder ball B is lowered.

The method for producing a printed wiring board according to the present invention includes:
Preparing a printed wiring board in which a cavity is formed in the first main surface and the connection pads are exposed on the bottom surface of the cavity;
Forming a flux layer on the connection pads;
Disposing a ball mounting mask having an opening at a position corresponding to the connection pad above the first main surface and having a flat bottom surface facing the first main surface;
Mounting solder balls on the flux layer through the openings of the ball mounting mask.

Sectional drawing which shows the manufacturing method of the printed wiring board of one Embodiment of this invention. Sectional drawing which shows the manufacturing method of the printed wiring board of one Embodiment of this invention. Sectional drawing which shows the manufacturing method of the printed wiring board of one Embodiment of this invention. Sectional drawing which shows the manufacturing method of the printed wiring board of one Embodiment of this invention. Sectional drawing which expanded a part of printed wiring board of FIG. Sectional drawing explaining the method to mount a solder ball on the printed wiring board which does not have a cavity using the conventional mask. Sectional drawing explaining the method to mount a solder ball on the printed wiring board which has a cavity using the conventional mask.

  An embodiment of a method for producing a printed wiring board of the present invention will be described with reference to the drawings. The method for manufacturing a printed wiring board according to the present embodiment includes steps described with reference to FIGS. 1 to 5, but may include other steps or processes before and after the steps or between each step.

  In the step shown in FIG. 1, a printed wiring board 10 having a cavity 12 formed in the first main surface 10A is prepared. The printed wiring board 10 in the illustrated example is a coreless substrate obtained by alternately laminating the conductor layers 14 and the resin insulating layers 16 on a support plate (not shown) and then removing the support plate. However, the printed wiring board 10 may be a substrate with a core formed by alternately laminating a conductor layer having a predetermined circuit pattern and a resin insulating layer on one side or both sides of the core substrate. Solder resist layers 18 and 20 are formed on the first main surface 10A and the second main surface 10B of the printed wiring board 10, and connection pads 22 are formed from openings 18a and 20a formed in the solder resist layers 18 and 20, respectively. 24 is exposed. A solder resist layer 26 is also formed on the bottom surface of the cavity 12, and the connection pads 28 are exposed from the openings 26 a formed in the solder resist layer 26.

  In the step shown in FIG. 2, the flux layer 30 is formed by applying flux on at least the connection pads 28 in the cavity 12, and in the illustrated example, on the entire bottom surface of the cavity 12. The flux layer 30 can be formed by printing or inkjet.

  In the step shown in FIG. 3, the ball mounting mask 32 is disposed adjacent to the upper side of the first main surface 10 </ b> A of the printed wiring board 10. The ball mounting mask 32 has an opening 32a at least at a position corresponding to the connection pad 28 in the cavity 12, and a lower surface 32d facing the first main surface 10A is formed flat. The shape of the upper surface 32u of the ball mounting mask 32 is not particularly limited, and may have a recess or a protrusion. In the illustrated example, the ball mounting mask 32 also has a flat upper surface 32u, that is, the thickness of the ball mounting mask 32 is constant. The thickness of the ball mounting mask 32 can be set to 7 μm to 20 μm, for example.

  In the step shown in FIG. 4, the solder balls B are mounted on the connection pads 28 with the flux layer 30 interposed by dropping the solder balls B through the openings 32 a of the ball mounting mask 32. In this way, a printed wiring board in which the solder balls B are mounted on the connection pads 28 in the cavity 12 can be manufactured. Thereafter, by reflowing the solder balls B, a printed wiring board having solder bumps formed on the connection pads 28 can be manufactured (not shown).

  According to the printed wiring board manufacturing method of the present embodiment, the solder ball B is mounted using the ball mounting mask 32 having a flat lower surface 32d, so that the flux in the cavity 12 is transferred from the lower surface 32d of the ball mounting mask 32. The distance to the layer 30, that is, the falling distance under the non-guide from the time when the solder ball B leaves the ball mounting mask 32 until it reaches the flux layer 30 can be reduced, so that the mounting accuracy of the solder ball B can be improved. it can.

  A suitable thickness of the flux layer 30 will be described with reference to FIG. FIG. 5 is an enlarged cross-sectional view showing a part of the printed wiring board shown in FIG. As described above, by using the ball mounting mask 32 having a flat lower surface 32d, the falling distance under the non-guide until the solder ball B leaves the ball mounting mask 32 and reaches the flux layer 30 in the cavity 12 is as follows. And the mounting accuracy of the solder ball B is improved. However, the depth of the cavity 12 differs depending on the product. The deeper the cavity 12 is, the longer the falling distance of the solder ball B under the non-guide and the lower the mounting accuracy of the solder ball B. Therefore, in the step of forming the flux layer 30, the top of the solder ball B landed on the flux layer 30 in the later step is within the range of −15 μm to +15 μm with respect to the position of the upper surface 32 u of the ball mounting mask 32. It is preferable to adjust (set) the thickness t of the flux layer 30 so that Here, the “top portion of the solder ball B” means the highest part of the solder ball surface. The “thickness t of the flux layer 30” means the thickness of the flex layer 30 on the connection pad 28 in the cavity 12. The “−” (minus) side is the side from the upper surface 32 u to the lower surface 32 d of the ball mounting mask 32, and “+” (plus) is the opposite side.

  Further, in the step of forming the flux layer 30, the flux layer 30 is formed such that the top of the solder ball B landed on the flux layer 30 in the later step is positioned above the lower surface 32 d of the ball mounting mask 32. It is preferable to adjust (set) the thickness t. Thereby, the position shift of the solder ball B during the fall of the solder ball B and after landing can be prevented, and the mounting accuracy of the solder ball B can be further improved.

DESCRIPTION OF SYMBOLS 10 Printed wiring board 12 Cavity 14 Conductor layer 16 Resin insulation layer 18, 20, 26 Solder resist layer 22, 24, 28 Connection pad 30 Flux layer 32 Ball mounting mask 32a Opening 32d Lower surface 32u Upper surface

Claims (3)

A method of manufacturing a printed wiring board,
Preparing a printed wiring board in which a cavity is formed in the first main surface and the connection pads are exposed on the bottom surface of the cavity;
Forming a flux layer on the connection pads;
Disposing a ball mounting mask having an opening at a position corresponding to the connection pad above the first main surface and having a flat bottom surface facing the first main surface;
Mounting a solder ball on the connection pad through the opening of the ball mounting mask with the flux layer interposed therebetween. In the manufacturing method of the printed wiring board of Claim 1,
The flux layer is formed so that the top of the solder ball mounted on the flux layer is within a range of −15 μm to +15 μm with respect to the position of the upper surface of the ball mounting mask. Adjusting the thickness of the. In the manufacturing method of the printed wiring board of Claim 2,
Forming the flux layer includes adjusting the thickness of the flux layer so that the top of the solder ball is located above the lower surface of the ball mounting mask.

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