JP3339736B2 - Defect detection method for inner layer circuit of multilayer printed wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a defect in an inner layer circuit of a multilayer printed wiring board.

[0002]

2. Description of the Related Art In recent years, printed wiring boards have become more complicated and denser as semiconductor devices such as ICs and LSIs have become more highly integrated and sophisticated. On the other hand, the use of printed wiring boards is expanding, and they are widely used in large public systems. For this reason, higher reliability is required for printed wiring boards.

[0003] The layers in a multilayer printed wiring board are usually electrically connected by drilling a hole in an epoxy resin base material or a polyimide resin base material and performing through-hole plating. Resin may be melt-fixed to the cut surface of the inner copper foil by heat generated when drilling holes in the base material, and smear may occur. If the ductility of the copper foil mainly used for the inner layer is poor, cracks may be formed and the wire may be broken.

[0004] Since such cracks and smears cannot be seen from the outside, a test coupon is provided on a printed wiring board, the test coupon is cut out and poured into an epoxy resin, and through-hole plating and inner layer copper foil are applied. Are sequentially polished from rough abrasive paper to fine abrasive paper, finish polished using fine aluminum powder or the like, and observed using a microscope.

Prior to the observation, the sample after the final polishing was adjusted so that the concentration of ammonia and hydrogen peroxide was 25% by volume.
Observation was made after immersion in a soft etching solution comprising ammonia water 30, 30% hydrogen peroxide solution 1 and pure water 60.

[0006]

However, it is difficult to control the time of immersion in the soft etching solution, and the etching proceeds excessively, so that the boundary between the through-hole copper plating and the inner layer copper foil may appear. And the plating boundary line could not be determined, and the defect was sometimes overlooked.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a soft etching method for detecting a defect in an inner layer circuit of a multilayer printed wiring board without forming a boundary between the through-hole copper plating and the inner layer copper foil.

[0008]

According to the present invention, the concentration of ammonia and hydrogen peroxide is determined by mixing 25% aqueous ammonia 25 to 35%, 30% aqueous hydrogen peroxide 4 to 8 and pure water 60 by mixing volume ratio. The method is characterized in that a soft etching solution is applied to the surface of a sample and then washed with water. The amount of application may be such that it can be applied with a cotton swab.
It may be about 0 seconds.

[0009]

The etching solution containing ammonia and hydrogen peroxide oxidizes copper to form an ammine complex and dissolves copper. The dissolution rate becomes smaller in the order of a portion having a defect such as a crack or smear, a plating boundary line, and a normal portion. Etching is finished with the defect enlarged by etching by applying an etching solution with a large amount of hydrogen peroxide to the surface, preventing excessive dissolution and washing before the plating boundary line appears Then, only the defective portion is easily detected. An etching solution containing a small amount of hydrogen peroxide has a mild effect and dissolves copper on average, so that such a difference cannot be made.

[0010]

EXAMPLE A test piece was cut out of a glass epoxy resin substrate and a four-layer printed wiring board so as to include a through hole. The test piece was set on a casting ring, cast with an epoxy resin, and cured at room temperature. Then, the sample piece was taken out of the ring, polished with abrasive paper, and precision polished with alumina powder.

Next, 25% ammonia water 3
A soft etching solution of 0, pure water 60, and 30% hydrogen peroxide solution 5 was prepared, and this solution was applied with a cotton swab.
It was dried, set on a microscope, and observed. as a result,
No plating boundary line appeared, and only the cracks were magnified and observed.

Comparative Example 25% ammonia water 30 by volume ratio, pure water 60, 30%
A soft etching solution of a hydrogen peroxide solution 1 was prepared, and the same test piece as in the example was immersed in the solution for 20 seconds, washed with water, dried, set on a microscope, and observed. As a result, the boundary between the through-hole plating and the inner layer copper foil appears,
It was impossible to find smears.

[0013]

As described above, according to the method for detecting a defect of an inner layer circuit of a multilayer printed wiring board according to the present invention, since no plating boundary line appears, the inner layer copper foil and the through-hole plating and the inner layer copper foil are removed. Defects occurring in between can be reliably detected.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-55-122874 (JP, A) JP-A-63-274881 (JP, A) JP-A-64-52089 (JP, A) JP-A-4- 56391 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 1/32 H05K 3/00 H05K 3/46 JICST file (JOIS)

Claims (1)

(57) [Claims] 1. A soft etching solution comprising 25% aqueous ammonia 25 to 35%, 30% aqueous hydrogen peroxide 4 to 8 and pure water 60 at a mixed volume ratio of ammonia and hydrogen peroxide is applied to the sample surface. A method for detecting defects in an inner layer circuit of a multilayer printed wiring board, wherein the method is carried out after the coating is performed.