JPS6319895A - Printed wiring board - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is directed to 7. A method for preventing bridging and short circuits between printed circuit patterns during the soldering process for printed wiring boards used in slave devices, especially for component mounting. It is related to.

[Conventional technology]

As is well known, conventional printed wiring boards of this type are made of a combination of a thermosetting resin such as epoxy or phenol and a reinforcing material such as low-temperature glass cloth. After coating a photosensitive resist on the conductor foil surface of a conductor can (h1 layer plate) covered with a conductor foil such as steel, a circuit pattern is recorded by photography or screen printing, and a predetermined pattern is etched by an etching method. It is manufactured by a process in which a solder resist or mark is printed on it, holes are drilled/outlined, etc., and flux is applied to complete the process.

FIG. 2 shows an enlarged cross-section of a main part of an example of a conventional printed wiring board in which components are mounted on the board, pins of the components are inserted into holes in the printed pattern, and soldered. The figure shows the most basic single-sided printed wiring board, with the side on which components are mounted being the bottom side and the soldering side being the -F side, with the front and back sides reversed. For clarity, each part 1 method is shown in i0 dilation, and the proportional relationship in the middle method is not strict. S is a substrate (thickness a) covered with a copper foil F (FJ Sab) forming a circuit pattern. R is a solder resist, which is applied to the entire surface of the pattern and the entire exposed portion of the etched back surface of the substrate, except for the predetermined soldering portions of the printed pattern. C indicates the film thickness of the solder resist. In addition, shi indicates the mounted parts, and P indicates the two bins (partially only two bins are shown. Usually, there are many consecutive bins, and there are also cases of flat bins.)
It is. The bottle P is inserted into a predetermined hole on the printed pattern, and the solder H is applied to electrically connect the bottle P and a predetermined portion of the pattern.

[Problem that the invention seeks to solve]

However, in recent years, with the general trend toward smaller size/higher performance of communication equipment and electronic equipment, mounting on printed wiring boards has become significantly smaller/higher density, and soldering by dipping etc. is no longer required between both pins in the process. Short cross-linking 171 (so-called bridging) has become a major problem.

-4- E) In the figure, when the distance between both pins d is small, the pattern distance e also becomes extremely small, and the shards H around the bottle P easily flow into the recess formed between the two bottles due to wettability. , when it flows here, the dotted line Ha due to surface tension
As shown in the figure, the soldering of both pin parts causes bridging at part H.

For example, the interval d between a large number of consecutive bins in an integrated circuit (IC) etc. is now 1.18m, compared to the initial 2.54+nm!
11. Furthermore, the size has been significantly reduced to (1.75 mm, etc.), and as a result, the dense pattern spacing e is now required to be on the order of 0.3 mm, etc.

On the other hand, if the length b of the copper foil is assumed to be 35 μm, the solder/resist skin Mu is Cζ5 μI, so the recess depth is approximately (35-5) = 30 μm, and the figure also shows that the bridging capacity is 1iJ. It can be seen that the gender is large.

When a single printed wiring board has an extremely large number of micro-bin intervals, this bridging is actually responsible for approximately half of the causes of defects that reduce the direct pass rate (unconditional pass rate) of products. Since bridging occurs at unspecified locations during PF purchase, it takes an extremely large amount of man-hours/time to find the defective location for correction, which significantly reduces productivity/economic efficiency. was.

For example, a "double mask method" has been proposed for the purpose of reducing the possibility of occurrence of the bridging phenomenon as described above. FIG. 3 shows a diagram corresponding to FIG. 2. IJ components that are the same or similar to those in FIG. 2 are designated by the same reference numerals.

This proposal is to apply a secondary solder resist film Ra similar to the original film R only to the necessary parts of the solder resist film 11Q R of the conventional example shown in Fig. It is something.

However, in such conventional proposals, even if double coating of solder resist is applied to the recess between the bins, which is the cause of the bridging phenomenon, the thickness of the second solder resist film is The original primary skin I+! 2 thickness d
The depth of the recess is (b-2d), and if the values of b and d are the same as in the example in Fig. 2, the depth of the recess is (
35-10) = 25 μm, which is shallower by 5 μm and has an apparent effect due to the decrease in absolute value compared to 30 μm in the conventional example, but in reality, it does not fundamentally solve the problem. It is obvious that it is not something that can be obtained.

The present invention is applicable to the above-mentioned conventional example <including the proposed example described in nH)
This was done in consideration of the problem, and it is intended to fundamentally eliminate the occurrence of the 00 bridging phenomenon, and also to provide a convenient position for mounting components [4].
It has been the target.

(Step F to solve the problem) Therefore, in the present invention, after applying an ink film containing a foaming agent to the locations where the bridging prevention IF is required close to each other in the conductor foil circuit pattern, the film is heated to a predetermined temperature. The purpose is to achieve the above object by heating the ink portion to expand the volume of the ink portion beyond the thickness of the conductor foil.

[Effect]

Therefore, the recess between both pins is not only completely filled, but also rises up between them to form a barrier, eliminating the fear of solder flowing in, so the bridging of the solder part between both pins is completely completed. In addition, the raised barrier between the parts helps in positioning the mounted parts when setting them.

〔Example〕

Hereinafter, the invention will be explained based on examples.

Figure 1 does not show the main parts of a single-sided printed wiring board embodying the present invention, but is a diagram corresponding to Figure 2.31A, and the same or equivalent components as in Figure 2.3 are denoted by the same reference numerals, and redundant explanations are given. is omitted. In addition, each dimension a, b, c in Figure 2
, d, etc. are assumed to have substantially similar values.

(Structure) R1 indicated by the dotted line is the solder resist film R that is completely covered on the etched printed circuit board except for the areas scheduled for soldering, and there are four small gaps between patterns that require bridging prevention. The present invention is characterized by a heat-resistant solder/resist ink such as a phenol or epoxy-based solder resist ink that is selectively overlaid and printed on.
This ink contains a suitable blowing agent in a predetermined ratio.

(Operation/Function) After completing the secondary printing using the ink as described above, when this printed wiring board is heated at a temperature specified for the ink/foaming agent, the secondary printing ink portion will be heated as shown in the figure. , the included blowing agent causes volumetric expansion, which not only fills the four parts, but also 1. It builds up and protrudes in both directions, forms a barrier R2 between the two bottles and solidifies, completely blocking the space between the solder 8 on both the bottles and eliminating the possibility of bridging.

Furthermore, these parts also serve as visual marks when setting loaded items, and the conventional printing of additional marks for this purpose can be omitted.

(Other Examples) In Example F, the secondary film of solder resist ink containing a foaming agent was explained, but the present invention
Without being limited to this, an ink containing a foaming agent can be used in place of the primary coating, with the coating order reversed, or applied entirely alone to the substrate. The same effect can be obtained.

Moreover, although the printed wiring board has been described as a single-sided type, it goes without saying that it can also be applied to a double-sided type or a multilayer type.

〔Effect of the invention〕

As explained above, according to the present invention, a barrier of foamed ink is formed in the gap between the circuit patterns of the conductor in close proximity to the circuit pattern, so that cross-linking and short-circuiting of the solder between them can be completely prevented. As a result, the productivity and straight-through rate of printed wiring board mounting work have been significantly improved.

[Brief explanation of the drawing]

FIG. 1 is an enlarged sectional view of a main part of a printed wiring board embodying the present invention, and FIGS. 2 and 3 are views corresponding to FIG. 1 of a conventional example and a conventional proposed example, respectively. S...Substrate F...Copper (conductor) foil (circuit pattern)
H-...Solder R...Solder resist R1...
・Foaming ink R2---------Barrier P・Shaft...Bottling......Implemented parts

Claims (1)

[Claims] An ink film containing a foaming agent is applied between adjacent conductor foil circuit patterns on a substrate of a printed wiring board, and the volume of the ink is expanded by heating the printed wiring board. Printed wiring board.