A processing method for silk screen solder mask of ultra-thick copper printed circuit board

Abstract

The invention provides a processing method for silk-screen solder resist of an ultra-thick copper printed circuit board, comprising the following steps: step 1, chemically treating the surface of a printed circuit board by using a chemical treatment solution; step 2, medium-temperature treatment: putting the printed circuit board into an oven for pre-baking for a certain time; step 3, pre-filling: filling the solder resist printing material into the gap of a circuit pattern under a vacuum state; step 4, putting the pre-filled printed circuit board into an oven for high-temperature curing, and setting the parameters of the high-temperature curing according to the material of the solder resist printing material; step 5, chemically treating the surface of the printed circuit board by using a chemical treatment solution; step 6, silk-screen printing: using a screen and a scraper to silk-screen the solder resist printing material onto the surface of the printed circuit board; step 7, pattern transfer: completing the pattern transfer by exposure and development, exposing the copper skin and circuit to be soldered, and protecting the unexposed area with the solder resist printing material; step 8, putting the printed circuit board after the pattern transfer into an oven for high-temperature curing.

Description

Technical Field

[0001] The invention belongs to the preparation process technology of a printed circuit board, and specifically relates to a processing method of silk-screen solder mask for an ultra-thick copper printed circuit board. Background Art

[0002] Solder mask is a material printed on the finished printed circuit board. Its function is to prevent circuit corrosion, prevent the degradation of circuit insulation performance caused by moisture, prevent solder from adhering to unnecessary parts, and prevent copper from contaminating the solder tank.

[0003] When printing solder mask on ultra-thick copper printed circuit boards, because the copper thickness is too thick, usually the copper thickness is more than 0.21mm, the use of conventional screen printing technology will result in abnormal conditions such as no oiling and ink bubbles.

[0004] This is mainly because when the circuit and copper foil are too thick, there will be a thickness difference in the gap between the copper foils during printing. When the printing material is squeezed and printed by the scraper and the printing material leaked from the screen is filled into the gap, the amount of oil applied is far less than the printing material required for filling, and there is a large amount of air in the gap that cannot be discharged, resulting in defects such as no oil application and ink bubbles in the finished product.

[0005] Therefore, it is necessary to design a new processing method for silk screen solder mask of ultra-thick copper printed circuit boards. Summary of the invention

[0006] The purpose of the present invention is to provide a processing method for silk-screen solder mask of an ultra-thick copper printed circuit board, so as to solve the problem proposed in the background technology that when the thickness of the circuit and the copper sheet is too thick, there will be a thickness difference in the gap between the copper sheets during printing, and the printing material is squeezed and printed by a scraper, and when the printing material leaked from the screen is filled into the gap, the amount of oil applied is far less than the printing material required for filling, and there is a large amount of air in the gap that cannot be discharged, resulting in problems such as no oil application, ink bubbles, etc. in the finished product.

[0007] The technical solution of the present invention is a method for processing a super-thick copper printed circuit board by silk screen printing solder mask, comprising the following steps:

[0008] Step 1: First chemical treatment: Use chemical treatment solution to carry out the first chemical treatment on the printed circuit board surface;

[0009] Step 2: Medium temperature treatment: put the printed board into the oven for pre-baking for a certain period of time;

[0010] Step 3, pre-filling: fill the gaps between the circuit patterns with solder resist in a vacuum state;

[0011] Step 4: First high temperature curing: Place the pre-filled printed board into the oven for high temperature curing, and set the high temperature curing parameters according to the solder mask printing material;

[0012] Step 5, second chemical treatment: use chemical treatment solution to carry out second chemical treatment on the surface of the printed circuit board;

[0013] Step 6, screen printing: Use a screen and a scraper to screen print the solder mask onto the surface of the printed board;

[0014] Step 7, pattern transfer: complete the pattern transfer through exposure and development, expose the copper foil and circuits that need to be soldered, and protect the unexposed areas with solder mask printing material;

[0015] Step 8: Second high temperature curing: Place the printed board after pattern transfer into an oven for high temperature curing.

[0016] In a specific implementation, in step 3, the pre-filling process includes:

[0017] A. First, design the filling film according to the gaps that need to be filled with printing materials on the exposed board surface;

[0018] B. Transfer the designed film to the screen;

[0019] C. Modulate solder resist printing material;

[0020] D. Use the screen with transferred film to pre-fill the solder mask.

[0021] In a specific embodiment, the chemical treatment solution is a mixed solution of dilute sulfuric acid and hydrogen peroxide.

[0022] In a specific embodiment, in the chemical treatment water, the concentration of sulfuric acid is 3% to 7%, and the concentration of hydrogen peroxide is 3% to 4.2%.

[0023] In a specific embodiment, the temperature of the chemical treatment solution during use is 32-38°C.

[0024] In a specific embodiment, the speed at which the chemical treatment solution performs chemical treatment on the surface of the printed circuit board is 2-2.5 m / min.

[0025] In a specific embodiment, during the medium temperature treatment in step 2, the temperature of the printed board to be pre-baked in the oven is 72-78° C., and the pre-baking time is 8-12 minutes.

[0026] In a specific embodiment, the high temperature curing is divided into four stages for curing. The temperature of the first stage of high temperature curing is 70-80°C, the temperature of the second stage of high temperature curing is 85-95°C, the temperature of the third stage of high temperature curing is 105-115°C, and the temperature of the fourth stage of high temperature curing is 145-155°C. The time of each stage of high temperature curing is 55-65 minutes.

[0027] In a specific implementation manner, the vacuum state in step 3 is a gas pressure ≤ 150Pa.

[0028] The beneficial effects of the present invention include:

[0029] The invention solves the problem that air exists in gaps during solder mask printing of ultra-thick copper printed circuit boards, resulting in no oil being applied to the gaps in finished products and ink bubbles existing in the gaps.

[0030] The present invention improves the bonding force between the solder resist printing material and the surface of the printed board by chemical treatment solution, forms an oxidized bonding layer on the copper surface of the printed board, and improves the bonding force between the copper surface and the solder resist printing material.

[0031] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0033] Figure 1 It is a cross-sectional schematic diagram of a printed circuit board after silk screen solder resist treatment in the present invention.

[0034] Among them, 1. Copper skin and circuit; 2. Solder mask printed material filled with vacuum plug holes; 3. Solder mask printed material for screen printing; 4. Substrate of printed circuit board. DETAILED DESCRIPTION

[0035] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] Example 1

[0037] A method for processing a super-thick copper printed circuit board with silk screen solder resist comprises the following steps:

[0038] Step 1: First chemical treatment: Use chemical treatment solution to carry out the first chemical treatment on the printed circuit board surface;

[0039] Step 2: Medium temperature treatment: put the printed board into the oven for pre-baking for a certain period of time;

[0040] Step 3, pre-filling: fill the gaps between the circuit patterns with solder resist in a vacuum state;

[0041] Step 4: First high temperature curing: Place the pre-filled printed board into the oven for high temperature curing, and set the high temperature curing parameters according to the solder mask printing material;

[0042] Step 5, second chemical treatment: use chemical treatment solution to carry out second chemical treatment on the surface of the printed circuit board;

[0043] Step 6, screen printing: Use a screen and a scraper to screen print the solder mask onto the surface of the printed board;

[0044] Step 7, pattern transfer: complete the pattern transfer through exposure and development, expose the copper foil and circuits that need to be soldered, and protect the unexposed areas with solder mask printing material;

[0045] Step 8: Second high temperature curing: Place the printed board after pattern transfer into an oven for high temperature curing.

[0046] In step 3, the pre-filling process includes:

[0047] A. First, design the filling film according to the gaps that need to be filled with printing materials on the exposed board surface;

[0048] B. Transfer the designed film to the screen;

[0049] C. Modulate solder resist printing material;

[0050] D. Use the screen with transferred film to pre-fill the solder mask.

[0051] The chemical treatment solution is a mixed solution of dilute sulfuric acid and hydrogen peroxide. After the surface of the printed board is treated with the chemical treatment solution, an oxidized bonding layer is formed on the copper surface of the printed board, thereby improving the bonding strength between the copper surface and the solder resist printing material.

[0052] In the chemical treatment solution, the concentration of sulfuric acid is 5%, and the concentration of hydrogen peroxide is 3.6%. When the chemical treatment solution with this ratio is used for treatment, the combined conditions of the bonding force between the printed board surface and the solder resist printing material and the cost are optimal.

[0053] The temperature of the chemical treatment solution during use is 35° C. When the chemical treatment solution at this temperature is used for treatment, the bonding force between the printed board surface and the solder resist is optimal.

[0054] The speed of the chemical treatment solution for chemically treating the surface of the printed circuit board is 2-2.5 m / min. This speed can ensure that the micro-visual volume is about 1 μm, will not cause serious damage to the circuit, and can meet the requirements of bonding strength.

[0055] During the medium temperature treatment in step 2, the temperature of the printed board to be pre-baked in the oven is 72-78° C., and the pre-baking time is 8-12 minutes. Pre-baking can improve the bonding strength of the printed board to the solder resist printing material.

[0056] The high temperature curing is divided into four stages for curing, the temperature of the first stage of high temperature curing is 70-80°C, the temperature of the second stage of high temperature curing is 85-95°C, the temperature of the third stage of high temperature curing is 105-115°C, the temperature of the fourth stage of high temperature curing is 145-155°C, and the time of each stage of high temperature curing is 55-65 minutes. The curing with four stages of gradually increasing temperature is not only conducive to improving the bonding strength between the board surface to be printed and the solder resist printing material, but also can prevent the solder resist printing material from expanding and overflowing due to too fast temperature increase.

[0057] The vacuum state in step 3 is a gas pressure ≤ 150Pa.

[0058] The solder resist printing material includes solder resist ink.

[0059] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions and substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for processing ultra-thick copper printed circuit board silk screen solder mask, characterized in that: The following steps are involved: Step 1: First chemical treatment: Use chemical treatment solution to carry out the first chemical treatment on the printed circuit board surface; Step 2: Medium temperature treatment: put the printed board into the oven for pre-baking for a certain period of time; Step 3, pre-filling: fill the gaps between the circuit patterns with solder resist in a vacuum state; Step 4: First high temperature curing: Place the pre-filled printed board into the oven for high temperature curing, and set the high temperature curing parameters according to the solder mask printing material; Step 5, second chemical treatment: use chemical treatment solution to carry out second chemical treatment on the surface of the printed circuit board; Step 6, screen printing: Use a screen and a scraper to screen print the solder mask onto the surface of the printed board; Step 7, pattern transfer: complete the pattern transfer through exposure and development, expose the copper foil and circuits that need to be soldered, and protect the unexposed areas with solder mask printing material; Step 8: Second high temperature curing: put the printed board after pattern transfer into the oven for high temperature curing; The chemical treatment solution is a mixed solution of dilute sulfuric acid and hydrogen peroxide; in the chemical treatment solution, the concentration of sulfuric acid is 3% to 7%, and the concentration of hydrogen peroxide is 3% to 4.2%; the temperature of the chemical treatment solution during use is 32 to 38°C; the speed of the chemical treatment solution for chemically treating the surface of the printed circuit board is 2-2.5m / min.

2. The method for processing the silk screen solder mask of the ultra-thick copper printed circuit board according to claim 1, characterized in that: In step 3, the pre-filling process includes: A. First, design the filling film according to the gaps that need to be filled with printing materials on the exposed board surface; B. Transfer the designed film to the screen; C. Modulate solder resist printing material; D. Use the screen with transferred film to pre-fill the solder mask.

3. The method for processing the silk screen solder mask of the ultra-thick copper printed circuit board according to claim 1, characterized in that: During the medium temperature treatment in step 2, the temperature of the printed board to be put into the oven for pre-baking is 72-78° C., and the pre-baking time is 8-12 minutes.

4. The method for processing the silk screen solder mask of the ultra-thick copper printed circuit board according to claim 1, characterized in that: The high temperature curing is divided into four stages. The temperature of the first stage is 70-80°C, the temperature of the second stage is 85-95°C, the temperature of the third stage is 105-115°C, and the temperature of the fourth stage is 145-155°C. The time of each stage is 55-65 minutes.

5. The method for processing the silk screen solder mask of the ultra-thick copper printed circuit board according to claim 1, characterized in that: The vacuum state in step 3 is a gas pressure ≤ 150Pa.

Images