A circuit board manufacturing method for avoiding ion migration

Abstract

The present invention discloses a circuit board manufacturing method for avoiding ion migration, comprising the following steps: selecting a 1080 type glass fiber cloth material adapted for high multi-layer and high-density through-hole connection, pressing, cooling, and curing after being fully impregnated in epoxy resin, and obtaining a circuit board substrate; the spindle speed of the drill rig is ≥200kprm during drilling, the spindle swing is ≤20um, the air pressure is controlled at 0.6-0.7Mpa, the drill bit is selected to grind within two, and the control hole is thicker than ≤20um; during drilling design, according to the substrate glass fiber warp and weft, the row of holes is designed to be 45 ° angle so that it is not on a glass fiber bundle; after drilling, the hole wall is desmeared; hole metallization is carried out using black hole or conductive film process, and then copper plating is carried out to thicken. The circuit board manufacturing method for avoiding ion migration provided by the present invention controls the process from multiple aspects to avoid the formation of ion migration channels, thereby improving the quality of the product.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit board manufacturing, and in particular to a circuit board manufacturing method that avoids ion migration. Background Art

[0002] Conductive Anodic Filament (CAF) occurs when metals on a circuit board, such as copper, silver, and tin, ionize under certain temperature and humidity conditions and migrate through the insulation layer to the other side under the action of an electric field, resulting in a degradation of insulation performance. This failure mode typically occurs after copper plating adjacent through-holes. Improper control during the production process, such as the type of fiberglass cloth used, drilling method, drilling parameters, design, and environmental factors, can lead to the slow migration of copper ions along the fiberglass cloth, resulting in leakage.

[0003] During the circuit board manufacturing process, the main situations in which ion migration occurs are as follows: between holes, between holes and lines, between lines and lines, and between layers. Figure 1 In all four cases, ions migrate between the positive and negative electrodes, causing conduction between the insulation of the circuit board and leading to quality abnormalities such as leakage.

[0004] In view of this, it is necessary to provide a circuit board manufacturing method that can avoid ion migration to solve the above technical problems. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a circuit board manufacturing method that avoids ion migration, and to control the process from multiple aspects to avoid the formation of ion migration channels, thereby improving product quality.

[0006] The technical solutions of the present invention are as follows:

[0007] A method for manufacturing a circuit board to avoid ion migration comprises the following steps:

[0008] Select 1080 type glass fiber cloth material suitable for high-layer and high-density through-hole connection, fully impregnate it in epoxy resin, and then press, cool and solidify it to obtain the circuit board substrate;

[0009] When drilling, the spindle speed of the drilling rig should be ≥200kprm, the spindle swing should be ≤20um, the air pressure should be controlled at 0.6-0.7Mpa, the drill bit should be within the second grinding range, and the hole diameter should be controlled at ≤20um. When designing the drilling holes, the holes should be arranged at a 45° angle according to the warp and weft directions of the glass fibers on the substrate so that they are not on the same glass fiber bundle.

[0010] After drilling, the hole wall is desmeared. For double-sided circuit board desmearing, the bath temperature is controlled at 75±3℃. The desmearing solution used includes potassium permanganate / sodium permanganate with a concentration of 40-60g / L and sodium hydroxide with a concentration of 35-45g / L. The desmearing amount is 0.05-0.25mg / cm 2 For desmearing of multi-layer circuit boards, the bath temperature is controlled at 85±3°C. The desmearing solution used includes potassium permanganate / sodium permanganate with a concentration of 75-85g / L and sodium hydroxide with a concentration of 48-58g / L. The desmearing amount is 0.15-0.4mg / cm 2 In the desmear process, the hexavalent manganese in the by-product is controlled to be less than 25g / L;

[0011] Specifically, when desmearing double-sided circuit boards, the concentration of potassium permanganate / sodium permanganate is 40g / L, 50g / L or 60g / L, or other values ​​within the range; the concentration of sodium hydroxide is 35g / L, 40g / L or 45g / L, or other values ​​within the range; the desmearing amount is 0.05mg / cm 2 , 0.1mg / cm 2 , 0.15mg / cm 2 , 0.2mg / cm 2 or 0.25 mg / cm 2 , or other values ​​within this range;

[0012] When desmearing a multilayer circuit board, the concentration of potassium permanganate / sodium permanganate is 75g / L, 80g / L or 85g / L, and the concentration of sodium hydroxide can be 48g / L, 50g / L, 52g / L, 55g / L or 58g / L, or other values ​​within this range; the desmearing amount is 0.15mg / cm 2 , 0.2mg / cm 2 , 0.3mg / cm 2 or 0.4 mg / cm 2 , or other values ​​within this range;

[0013] The black hole or conductive film process is used for hole metallization, and then copper plating is performed to thicken the hole. The black hole or conductive film process forms an insulating layer between the electroplated copper and the hole wall to prevent metal ion migration.

[0014] Furthermore, the vacuum pressure of the drilling rig during drilling is controlled at -10 to -16 KPa, such as -10 KPa, -12 KPa, -14 KPa or -16 KPa, or other values ​​within the range.

[0015] Furthermore, when the circuit boards are stored, the ambient temperature is controlled at 16-26°C and the humidity is controlled at 40-70%; wherein, the storage ambient temperature can be 16°C, 20°C, 25°C or 16°C, or other values ​​within this range; the humidity can be 40%, 50%, 60% or 70%, or other values ​​within this range.

[0016] Furthermore, when the circuit board is a multi-layer board, an annular ring design is added to the inner layer.

[0017] Furthermore, when designing the hole layout, the minimum hole spacing is determined by testing the ion migration failure time of different hole spacings.

[0018] Furthermore, the test conditions are: under the conditions of temperature 85° C., humidity 85%, and DC voltage 50V, the ion migration resistance is achieved for 1000 hours.

[0019] Compared with the prior art, the circuit board manufacturing method for avoiding ion migration provided by the present invention has the following beneficial effects:

[0020] 1. The circuit board manufacturing method for avoiding ion migration provided by the present invention can effectively avoid ion migration by controlling the type of substrate material used, drilling parameters, desmear parameters, hole metallization method, hole layout design, minimum hole spacing design and other processes during the production process, thereby improving product quality.

[0021] 2. The circuit board manufacturing method for avoiding ion migration provided by the present invention establishes a mechanism to prevent ion migration from the storage conditions, preventing the material from absorbing moisture and providing a channel for metal ion migration. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0023] Figure 1 Schematic diagram of several forms of ion migration in the prior art;

[0024] Figure 2 This is a schematic diagram of the pulling effect after drilling holes in glass fiber cloth of different thicknesses;

[0025] Figure 3 It is a schematic diagram of drilling holes;

[0026] Figure 4 This is a schematic diagram of the effect of the pore wall erosion degree on the formation of ion migration channels;

[0027] Figure 5 This is a schematic diagram of the ion migration isolation wall formed on the hole wall after drilling. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention and to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the specific implementation methods of the present invention are further described below.

[0029] It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] A method for manufacturing a circuit board to avoid ion migration comprises the following steps:

[0031] (1) Selecting 1080 type glass fiber cloth material suitable for high-layer and high-density through-hole connection, fully impregnating it with epoxy resin, and then pressing, cooling, and curing it to obtain a circuit board substrate;

[0032] Experiments have shown that if the density of the glass cloth is poor, metal ions will migrate through the loose gauze channels; in terms of CAF resistance, the looseness of the glass fiber needs to be considered, so the present invention selects a glass fiber cloth with better density.

[0033] Since drilling will cause a pulling force on the sheet material, which will damage the solidified dielectric layer, the pulled glass fiber filaments after electroplating will form ion migration channels after copper plating. Through experiments, it was found that the pulling effect of thin 1080 glass cloth is significantly smaller than that of thick 7628 glass cloth. Figure 2 Therefore, in the present invention, the substrate is selected to be 1080 type glass fiber cloth suitable for high multi-layer and high-density through-hole connection.

[0034] (2) When drilling, the spindle speed of the drill rig is ≥200kprm, the spindle swing is ≤20um, the air pressure is controlled at 0.6-0.7Mpa, the vacuum pressure is controlled at -10~-16Kpa, the drill bit is selected within the second grinding, and the hole coarseness is controlled to be ≤20um. By limiting the drilling rig and drilling parameters, it is possible to prevent the drilling process from pulling the glass fiber and forming an ion migration channel after the hole is metallized; when designing the drilling, according to the longitude and latitude of the substrate glass fiber, the hole arrangement is designed to be 45° angle, so that it is not on a glass fiber bundle, thereby preventing the metal ions from migrating along the glass fiber bundle. The drilling arrangement is as follows Figure 3 As shown;

[0035] At the same time, during hole layout design, the minimum hole spacing was determined by testing the ion migration failure time of different hole spacings. The test conditions were: temperature 85°C, humidity 85%, and DC voltage 50V, achieving 1000 hours of ion migration resistance.

[0036] Preferably, when the circuit board is a multi-layer board, a hole ring design is added to the inner layer to prevent mechanical force from pulling the hole wall during the drilling process, thereby preventing the formation of ion migration channels after metallization.

[0037] (3) After drilling, the hole wall is desmeared. For double-sided circuit board desmearing, the bath temperature is controlled at 75°C. The desmearing solution used includes potassium permanganate / sodium permanganate with a concentration of 50g / L and sodium hydroxide with a concentration of 40g / L. The desmearing amount is 0.1mg / cm 2 For desmearing of multi-layer circuit boards, the bath temperature is controlled at 85°C, the desmearing solution used includes 80g / L potassium permanganate / sodium permanganate and 55g / L sodium hydroxide, and the desmearing amount is 0.3mg / cm 2 In the desmear process, the hexavalent manganese in the by-product is controlled to be less than 25g / L;

[0038] Because the drill bit rotates at high speed, the hole wall after drilling is covered with a layer of drill smear, which needs to be cleaned before metallization. The present invention can effectively avoid the problem of ion migration channel formed by chemical erosion of the hole wall by controlling the composition and concentration of the desmear solution and the amount of desmear. Figure 4 As shown in the figure, the more times the adhesive is removed, the greater the erosion of the hole wall, the greater the probability of ion migration channels forming between holes, and thus the greater the probability of ion migration causing circuit board failure. Therefore, it is necessary to prevent the formation of ion migration channels by controlling the amount of adhesive removed.

[0039] (4) Use black hole or conductive film process to metallize the hole, and then perform copper plating to thicken it. The black hole or conductive film process forms an insulating layer between the electroplated copper and the hole wall, forming an ion migration isolation wall on the hole wall to prevent metal ion migration, such as Figure 5 As shown;

[0040] (5) When storing the circuit board after production, the ambient temperature should be controlled at 25°C and the humidity should be controlled at 40-70% to prevent the material from absorbing moisture and providing a channel for metal ion migration.

[0041] Therefore, the present invention establishes a mechanism to prevent ion migration by considering the type of substrate material used, drilling parameters, desmear parameters, hole metallization method, hole layout design, minimum hole spacing, storage conditions, etc., and makes special control over the mode in which ion migration causes circuit board failure, so that the prepared circuit board effectively avoids the problems caused by ion migration and improves product quality.

[0042] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. It is apparent to those skilled in the art that various changes, modifications, substitutions, and variations made to these embodiments without departing from the principles and spirit of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for manufacturing a circuit board to avoid ion migration, characterized in that: The steps include: Select 1080 type glass fiber cloth material suitable for high-layer and high-density through-hole connection, fully impregnate it in epoxy resin, and then press, cool and solidify it to obtain the circuit board substrate; When drilling, the spindle speed of the drilling rig should be ≥200kprm, the spindle swing should be ≤20um, the air pressure should be controlled at 0.6-0.7Mpa, the drill bit should be within the second grinding range, and the hole diameter should be controlled at ≤20um. When designing the drilling holes, the holes should be arranged at a 45° angle according to the warp and weft directions of the glass fibers on the substrate so that they are not on the same glass fiber bundle. After drilling, the hole wall is desmeared. For double-sided circuit board desmearing, the bath temperature is controlled at 75±3℃. The desmearing solution used includes potassium permanganate / sodium permanganate with a concentration of 40-60g / L and sodium hydroxide with a concentration of 35-45g / L. The desmearing amount is 0.05-0.25mg / cm 2 For desmearing of multi-layer circuit boards, the bath temperature is controlled at 85±3°C. The desmearing solution used includes potassium permanganate / sodium permanganate with a concentration of 75-85g / L and sodium hydroxide with a concentration of 48-58g / L. The desmearing amount is 0.15-0.4mg / cm 2 In the desmear process, the hexavalent manganese in the by-product is controlled to be less than 25g / L; The hole metallization is carried out by using black hole or conductive film process, and then the copper is electroplated to thicken the hole. The black hole or conductive film process forms an insulating layer between the electroplated copper and the hole wall.

2. The method for manufacturing a circuit board for avoiding ion migration according to claim 1, characterized in that: When drilling, the vacuum pressure of the drilling rig is controlled at -10 to -16Kpa.

3. The method for manufacturing a circuit board for avoiding ion migration according to claim 1, characterized in that: When storing circuit boards, the ambient temperature should be controlled at 16-26°C and the humidity should be controlled at 40-70%.

4. The method for manufacturing a circuit board for avoiding ion migration according to claim 1, characterized in that: When the circuit board is a multi-layer board, an annular ring design is added to the inner layer.

5. The method for manufacturing a circuit board for avoiding ion migration according to claim 1, characterized in that: When designing the hole layout, the minimum hole spacing is determined by testing the ion migration failure time of different hole spacings.

6. The method for manufacturing a circuit board for avoiding ion migration according to claim 5, characterized in that: The test conditions are: temperature 85°C, humidity 85%, DC voltage 50V, and 1000 hours of ion migration resistance.

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