JP3543094B2 - Pre-solder layer forming method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
This invention relates to pre-solder layer forming method for the printed wiring board pads, in particular, the height from the substrate to be mixed in the printed circuit board to have different types of pads on the surface, the print wiring substrate surface The present invention relates to a preliminary solder layer forming method for forming a preliminary solder layer having a constant height.
[0002]
[Prior art]
As a method of mounting an electronic component on a printed wiring board, soldering is generally used. In the case of such soldering, a solder layer is formed in advance on lead terminals of electronic components to be mounted and pads of a printed wiring board.
In order to form this preliminary solder layer, generally, there are a plating method, a dipping method (solder dipping method), a solder paste printing method, and the like.
The most common solder paste printing method for forming a preliminary solder layer on a pad is to print a solder paste on a pad provided for wiring on a printed wiring board using a mask screen and apply a preliminary solder on the pad. This is a method of forming a layer.
[0003]
However, with the increase in mounting density and the application of build-up boards, pads on printed wiring boards have been placed at narrow pitches and fine vias have been attached to the pads, and pads with complicated shapes have been added. If they are mixed irregularly, it is difficult to cope with the above-mentioned solder paste printing method.
An electroless plating method can be considered as a suitable method for forming a solder layer when the arrangement of pads on a printed wiring board is high-density and complicated. However, in the electroless plating method, the thickness of the formed solder layer is small and a preliminary solder layer is used. It is difficult to secure the thickness required for the process, and the cost required for processing is high.
[0004]
FIG. 3 shows a conventional method obtained by improving the above method. FIG. 3 is a cross-sectional view for explaining steps of a conventional example of a method of forming a preliminary solder layer on a small pitch interval pad. First, as shown in the lower part of the FIG. 3 (a), a multi-stage number of the BGA 0.2mm pitch (Ball Grid Array) pads (conductor thickness 20 [mu] m, the pad diameter 110 [mu] m) known build a printed wiring board 50 having a Created by the up method.
[0005]
As apparent from FIG. 3 (a), the printed circuit board 50 has two pad or to form the preliminary solder layer on its upper surface, a flat pad 60, a pad 70 having a microvia . Then, at positions corresponding to the pads 60, 70 of the printed wiring board 50 is prepared a glass mask 80 having an opening 8 6.
[0006]
Each opening 8 6, filling solder powder balls 90 (spherical diameter 0.1 mm) one by one. As shown in the upper part of FIG. 3A, a glass mask 80 filled with solder powder balls 90 is arranged on the printed wiring board 50, and the positions of the solder powder balls 90 match the positions of the pads 60 and 70. Set to
[0007]
The printed wiring board 50, when the alignment of the glass mask 80 filled with solder powder balls 90 is complete, the solder powder balls 90 filled in the opening 8 6 of the glass mask 80 open, the printed wiring board 50 pads Transfer to 60 and 70. After the transfer of the solder powder balls 90 to the pads 60 and 70, the printed wiring board 50 is heated at 240 ° C. to melt the solder powder balls 90, and as shown in FIG. Preliminary solder layers 96 and 97 (the thickness of the solder layer is about 40 μm) are formed thereon.
[0008]
When the preliminary solder layers 96 and 97 are formed by such a method, the solder powder balls 90 are transferred to the pads 60 and 70 of the printed wiring board 50 when filling the solder powder balls 90 into the glass mask 80 or from the glass mask 80. At this time, extra solder powder may adhere due to static electricity or the like, causing a short circuit between pads.
[0009]
When the flat pad 60 and the pad 70 having the fine via with the concave cross section are mixed as in the above-described printed wiring board, when the thickness of the solder layer is adjusted according to the flat pad 60, the fine via Since the solder layer is also filled in the fine vias in the pad 70 having the following, the amount of solder is insufficient to maintain the same height as the height of the pad 60.
[0010]
That is, the height of the solder layer 97 in the pad 70 having the fine via is lower than the height of the solder layer 96 in the flat pad 60. Conversely, when the thickness of the solder layer is adjusted in accordance with the pad 70 having the fine via, the flat pad 60 may have an excessive amount of solder and cause a short circuit or the like.
[0011]
[Problems to be solved by the invention]
As shown in FIG. 3, the conventional method for forming a preliminary solder layer described above is sufficient to cause a short circuit when transferring solder particles from a glass mask to a pad of a printed wiring board, and the height from the board is small. In a printed wiring board in which a plurality of different types of pad groups are mixed, it is difficult to form a preliminary solder layer having the same height on all the pads.
[0012]
The present invention has been made to solve the above problems, and a plurality of types of pad groups having different heights from the substrate are mixed. Particularly, in a printed wiring board having a small pitch between the pads, a short circuit may occur. An object of the present invention is to provide a method for forming a preliminary solder layer that can form a preliminary solder layer having a similar height on all pads without performing the method.
[0013]
[Means for Solving the Problems]
That is, in the method for forming a preliminary solder layer according to the present invention, in the method for forming a preliminary solder layer on a surface of a plurality of types of pad groups having different heights from a substrate mixed on a printed wiring board, By masking a plurality of different types of pad groups with a resin layer of a certain height from the substrate surface, and removing the resin layer from the surface of the lowest type of pad group from the substrate by removing the resin layer A temporary preliminary solder layer is formed such that the pad surface is exposed and the height from the substrate is substantially the same as the pad surface of the second lowest kind of pad group with respect to the pad surface. a method in which, successively performs the height ascending order from the substrate, up to a height that second highest type of pads from the substrate, to repeat the process, the high from the substrate of all kinds of pads Almost the same A step to be to expose the pad surface by removing the resin layer from the surface of the height highest types of pads from the substrate, for the pads of all kinds, of the resin layer Forming a preliminary solder layer having a fixed height regulated by the height ”(claim 1), whereby the above object can be achieved.
[0014]
Further, the method for forming a preliminary solder layer according to the present invention includes the method for forming a preliminary solder layer on a surface of a plurality of types of pad groups having different heights from a substrate mixed on a printed wiring board; and lowest type of process the pad group other than pad group masked with a resin layer of a predetermined height from the substrate surface, with respect to the front surface of the height lowest types of pads from the substrate, from the substrate The method of forming a temporary preliminary solder layer so that the height of the pad is almost the same as the pad surface of the pad group of the second lowest kind is sequentially performed in the order of height from the substrate. , the height from the substrate to second highest type of pad groups, to repeat the method comprising the steps of substantially the same height the height of the substrate for all kinds of pads, the high from the substrate From the surface of the pad group of the highest kind Serial to expose the pad surface by removing the resin layer, for the pads of all kinds, and a step of forming a preliminary solder layer having a predetermined height is restricted by the height of the resin layer (Claim 2).
[0015]
further,
"The method for forming a preliminary solder layer according to claim 1 or 2, wherein in the step of exposing the pad, a corresponding portion of the resin layer is irradiated with a laser beam."
It is characterized by the following.
[0016]
(Action)
According to the above-described preliminary solder layer forming method, the solder paste for forming the preliminary solder layer is filled in order from the pad group of the lowest height from the substrate (the pad having a large filling capacity). Even when multiple types of pads with different heights are mixed, all the pads are applied under the same conditions when applying the solder paste, so when the application is completed, Is formed with a preliminary solder layer having a certain height regulated by the thickness of the resin layer.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a sectional view for explaining steps (a) to (d) of the embodiment of the preliminary solder layer forming method of the present invention.
FIG. 2 is a cross-sectional view for explaining steps (e) to (g) of the embodiment of the preliminary solder layer forming method according to the present invention.
[0018]
In this embodiment, a high-density printed wiring board is formed by a build-up method. In the process to be described, two types of pad groups having different heights from the printed wiring board 10 are mixed. It is assumed that a preliminary solder layer having a uniform height is formed on the pads 20 and 30 belonging to two types of pad groups having different heights from the substrate.
[0019]
First, the pad 20 and the pad 30 having the fine via 31 are formed on the printed wiring board 10 (FIG. 1A).
In this case, the pad 20 is formed with a small pitch of 0.2 mm, a diameter of 110 μm, and a pad interval of 90 μm, and the fine via 31 of the pad 30 is formed with a via diameter of 70 μm and a via depth of 60 μm.
[0020]
Next, a resin layer 40 for a solder mask is formed on the printed wiring board 10 (FIG. 1B). In this case, an epoxy thermosetting resin is applied by screen printing so that the thickness (height from the substrate surface) is about 30 to 40 μm on the pad 20, and then dried at 90 ° C. for 15 minutes. Since the thickness of the resin layer 40 applied by screen printing is about 30 to 40 μm, a sufficient thickness of the preliminary solder layer can be obtained as described later, and the partition wall between adjacent pads can be obtained. Thus, the preliminary solder layer can be prevented from bridging. The above-mentioned setting of the temperature and the time for the drying is performed so that the resin layer 40 is not completely cured and can be removed by a chemical treatment after forming the preliminary solder layer.
[0021]
As described above, since the regions where the pads 20 and 30 where the preliminary solder layers are to be formed are covered with the resin layer 40, first, the pads having the fine vias 31 (the filling volume of the solder paste is large) By irradiating the resin layer 40 at the position corresponding to 30 with a laser beam, an opening 41 having the same diameter as the via diameter is formed (FIG. 1C).
[0022]
The reason why the opening 41 is formed only at the position corresponding to the pad 30 having the fine via 31 is that an appropriate amount of solder supply differs depending on the specification of the pad (for example, the pad 20 and the pad 30 have different amounts of solder). This is for setting an appropriate amount of solder supply for each pad.
[0023]
In the case of FIG. 1, since there are two types of pad groups having different heights from the substrate, the process may be divided into pads 20 and pads 30, but three types of pad groups having different heights from the substrate may be used. In the above case (substantially, when the filling volume of the solder paste is different), the process is divided for each pad group having a different height from the substrate, and the via diameter is sequentially reduced from the one having the lower height from the substrate. It is necessary to form a combined opening and proceed with subsequent processing.
[0024]
After the opening 41 is formed in the resin layer 40 on the printed wiring board 10 as shown in FIG. 1C, a solder paste (the contained solder is Sn / Pb eutectic solder) is applied thereon. Apply. In this case, the amount of solder to be applied is equal to or more than the amount that satisfies the filling of the volume of the fine via 31 in order to uniformly fill the inside of the fine via 31, and the portion of the fine via 31 is supplied with a heat source. And a temporary preliminary solder layer 32 is formed on the pad 30 (FIG. 1 (d)). At this time, the heights of the pads 20 and the pads 30 from the substrate are substantially the same.
[0025]
In addition, since the solder paste is supplied to the pad 30 also in the subsequent process, the amount of solder in FIG. 1 (d) is the amount of solder paste required as a preliminary solder layer for the pad 30 having the fine via 31. It does not need to be supplied.
[0026]
When the formation of the temporary preliminary solder layer 32 on the pad 30 through the opening 41 is completed, the resin layer 40 at a position corresponding to the pad 20 is irradiated with a laser beam to have the same shape as the pad 20. An opening 42 is formed (FIG. 2E).
[0027]
After the opening 42 corresponding to the pad 20 is formed in the resin layer 40, a solder paste (the contained solder is Sn / Pb eutectic solder) is applied thereon. In this case, the solder is applied so that the amount of solder to be applied is substantially equal to or greater than the thickness of the mask resin layer 40 (the height from the substrate surface).
[0028]
After this application, heating is performed to form a preliminary solder layer 21 on the pad 20 and a preliminary solder layer 33 on the pad 30 (FIG. 2 (f)).
In this step, the solder paste has already been supplied to the fine via 31 of the pad 30 in the step shown in FIG. 1D, and the concave portion of the fine via 31 has been buried flat, so that the high via The heights of the pads 20 and 30 are almost the same, so that almost the same conditions are set for the application of the solder paste on the pads 20 and 30. In the step of FIG. The supply of the solder paste to 30 is performed in the same manner.
[0029]
In the step of FIG. 2F, the solder mask resin layer 40 which is not removed and partially remains is formed by partition walls between the preliminary solder layers formed on the pads arranged at minute pitch intervals. Is formed to prevent the preliminary solder layers from being short-circuited to each other.
[0030]
Further, the thickness of the resin layer 40 regulates the amount of solder so that the height of the formed preliminary solder layer is uniform. Since the supply of the solder paste to the pad 30 is performed in two separate applications, the sinking of the preliminary solder layer 33 of the pad 30 that tends to occur when the supply is performed only once does not occur.
[0031]
After the step of FIG. 2 (f), the mask resin layer 40 is removed by a chemical solution treatment, and a printed wiring board having the preliminary solder layers 21, 32 formed on the pads 20, 30 is completed (FIG. 2). (G)).
[0032]
In the above-described steps, the use of laser light for the resin layer 40 to form the opening facilitates the execution even when the opening pitch is fine. In addition, since the solder mask is formed of a resin layer, the thickness of the mask can be freely set, and it is easy to adjust the height of the preliminary solder layer that determines the amount of solder to an optimum height. Further, the mask resin layer left between the pads at minute pitch intervals serves as a partition wall between the preliminary solder layers, and prevents a mutual short circuit of the preliminary solder layers on the pads.
[0033]
In this embodiment, the pads 20 and 30 are all masked with the resin layer 40 at first, but since the solder paste is applied to the pad 30 first, the mask with the resin layer 40 is not shown in FIG. As described above, the masking may be performed such that only the pad 20 is masked. It is formed as shown in FIG. 1C and dried at 90 ° C. for 15 minutes, and thereafter, the process may be performed in the same manner as in the previously described embodiment. In that case, the step of exposing the pad 30 is reduced. Alternatively, parallel light may be used instead of laser light to form the opening 42.
[0034]
【The invention's effect】
As described in detail above, the present invention provides a method for forming a preliminary solder layer on the surface of a plurality of types of pad groups having different heights from a substrate mixed on a printed wiring board, wherein the heights from the substrate are different. A step of masking a plurality of types of pad groups with a resin layer having a certain height from the substrate surface, and removing the resin layer from the surface of the type of pad group whose height from the substrate is the lowest. And forming a temporary preliminary solder layer on the pad surface such that the height from the substrate is substantially the same as the pad surface of the pad group of the second lowest kind. the sequentially carried out at a height ascending order from the substrate, the height from the substrate to second highest type of pad groups, to repeat the process, the height from the substrate for all kinds of pads a step of substantially the same height Exposing the pad surface by removing the resin layer from the height of the highest kind of pads on the surface of the substrate, for the pads of all types, it is restricted by the height of the resin layer Forming a preliminary solder layer of a certain height, the pad is filled with the solder paste in order from the pad having the largest filling capacity, so that a plurality of types of pad groups having different heights are mixed. However, when applying the solder paste, all pad groups are applied under the same conditions, so when the application is completed, a certain height regulated by the thickness of the resin layer is placed on each pad group. A preliminary solder layer is formed. The use of the resin layer makes it easy to adjust the height of the preliminary solder layer (claim 1).
[0035]
Also, the present invention provides a method for forming a preliminary solder layer on a surface of a plurality of types of pads having different heights from a substrate mixed on a printed wiring board, wherein of a step of masking the pads from the substrate surface with a resin layer of uniform height, with respect to the front surface of the height lowest types of pads from the substrate, is the second lowest height from the substrate A method of forming a temporary preliminary solder layer so that the height is substantially the same as the pad surface of the type of pad group is sequentially performed in ascending order of height from the substrate, and the height from the substrate is two times. by high types of pads th, to repeat the process, all types comprising the steps of substantially the same height level from the pads of the substrate, height highest types from board pads By removing the resin layer from the surface of the group To expose the pad surface, against the pads of all types, forming a pre-solder layer of constant height regulated by the height of the resin layer, by having a pad filling capacity is large Since the solder paste is filled in order from the beginning, even if multiple types of pad groups with different heights are mixed, when applying the solder paste, all the pad groups are applied under the same conditions, When the application is completed, a preliminary solder layer having a certain height regulated by the thickness of the resin layer is formed on each pad group. The use of the resin layer makes it easy to adjust the height of the preliminary solder layer. Furthermore, the pad group with the largest filling volume is first exposed from the beginning, so that the number of steps for exposing can be reduced by that amount. The number is small (claim 2).
[0036]
In addition, the resin layer other than the resin layer removed for pad exposure serves as a partition wall that does not short-circuit the preliminary solder layer on the adjacent pad, and enables the arrangement of pads at a small pitch.
[0037]
In addition, by irradiating a laser beam, the resin layer is removed (an aperture is provided in the resin layer using a laser beam to expose a pad), thereby facilitating execution even when the opening pitch is fine. (Claim 3).
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating steps (a) to (d) of an embodiment of a method for forming a preliminary solder layer according to the present invention.
FIG. 2 is a cross-sectional view for explaining steps (e) to (g) of the embodiment of the preliminary solder layer forming method of the present invention.
FIG. 3 is a cross-sectional view illustrating a process of a conventional example of a method for forming a preliminary solder layer.
[Explanation of symbols]
Reference Signs List 10 printed wiring board 20, 30 pad 21, 32, 33 preliminary solder layer 31 fine via 40 resin layer 41, 42 for solder mask opening

Claims (3)

In the method of forming a preliminary solder layer on the surface of a plurality of types of pad groups having different heights from a board mixed on a printed wiring board,
A step of masking a plurality of types of pad groups having different heights from the substrate with a resin layer having a certain height from the substrate surface ,
The pad surface is exposed by removing the resin layer from the surface of the pad group having the lowest height from the substrate, and the height of the pad from the substrate is the second lowest for the pad surface. A method of forming a temporary preliminary solder layer so that the height is almost the same as the pad surface of the pad group is sequentially performed in order from the lowest height from the substrate, and the height from the substrate is the second highest. to a higher type of pad groups, to repeat the method comprising the steps of substantially the same height the height of the substrate for all kinds of pads,
Exposing the pad surface by removing the resin layer from the height of the highest kind of pads on the surface of the substrate, for the pads of all types, it is restricted by the height of the resin layer Forming a preliminary solder layer having a certain height. In the method of forming a preliminary solder layer on the surface of a plurality of types of pad groups having different heights from a board mixed on a printed wiring board,
A step of masking a pad group other than the pad group of the lowest type from the substrate with a resin layer having a certain height from the substrate surface ,
Against the front surface of the height lowest types of pads from the substrate, so that the height from the substrate is substantially the same height as the second low type of pad group of the pad surface, a temporary spare a method in which to form a solder layer sequentially performed in the order low height from the substrate, the height from the substrate to second highest type of pad groups, to repeat the process, of all kinds A step of making the height of the pad group from the substrate substantially the same ,
Exposing the pad surface by removing the resin layer from the height of the highest kind of pads on the surface of the substrate, for the pads of all types, it is restricted by the height of the resin layer Forming a preliminary solder layer having a certain height. The method according to claim 1, wherein the resin layer is removed by irradiating a laser beam.