How to improve the appearance quality of solder resist
Preface
When people talk about the development trend of printed boards, they often think that printed boards are developing towards high-precision, high-density, and reliability, which is the trend of development. On the other hand, users have increasingly strict requirements for the appearance of printed boards. Solder resist is like the "coat" of printed boards. In addition to having a certain thickness and hardness, solvent resistance tests, and adhesion tests that meet standards, it also requires a uniform surface color, a glossy finish (currently, the brighter the better in domestic guest rooms), no garbage, and no excess marks on the surface. It can be said that the appearance quality of solder resist is not only a reflection of a company's technical and management level, but also directly affects the company's "orders". Therefore, how to improve the appearance quality of solder resist for printed boards has become a problem that every printed board factory needs to solve. Based on my practical experience, I will discuss how to improve the appearance quality of solder mask from four aspects: screen printing, exposure, development, and post curing.
II. Factors affecting the appearance quality of solder resist
1. Silk screen printing:
During the screen printing process of photosensitive solder mask, the flatness of the scraper, the cleanliness of the screen printing environment, the use of screen sealing tape and ink preparation during screen printing, screen printing pressure, and the brush plate before screen printing can all affect the appearance quality. According to the actual production situation, the top three factors have the greatest impact. The uneven scraper can easily create scraper marks on the surface of the solder mask; Insufficient cleanliness in the screen printing room can easily generate garbage on the surface of the solder mask; Improper use of sealing tape can easily cause surface adhesive to dissolve in the solvent of the ink.
2. Exposure:
During the exposure process of solder mask ink, due to the incomplete solidification of the solder mask, it is easy to produce imprints when the solder mask film adheres to the solder mask, which is the main reason for affecting the appearance quality of the solder mask.
3. Development:
At present, the development of solder resist ink is generally carried out using a horizontal conveyor type. Due to the incomplete solidification of solder resist, the driving and pressing wheels of the development machine can easily cause damage to their surface, resulting in roller marks and affecting the appearance quality of solder resist. In addition, incorrect exposure energy can also affect the glossiness of the solder resist, but this can be controlled through a light wedge table.
4. Post curing
Uneven temperature during post curing of solder mask can easily cause uneven color of solder mask. When the temperature is too high, it can even cause local yellowing and blackening, affecting the appearance of solder mask.
Improve the appearance quality of solder resist from four aspects
1. Silk screen printing:
When using silk screen solder resist ink, due to the uneven surface of the silk screen, after a period of silk screen printing, the surface of the scraper will become uneven, leaving a scraper mark on the solder resist surface. Therefore, the operator must pay attention to the surface condition at all times. Once any scratches are found, the scraper should be immediately reground to ensure its flatness.
We conducted parallel experiments to address the issue of surface adhesive particles on solder resist. Select two different types of tape for screen sealing, use two types of solder resist ink for screen printing, and observe the condition of surface adhesive particles, as shown in Table 1.
From the above experimental results, it can be seen that tape A has a good combination effect with ink B, while tape B has a good combination effect with both ink A and ink B
When people talk about the development trend of printed boards, they often think that printed boards are developing towards high-precision, high-density, and reliability, which is the trend of development. On the other hand, users have increasingly strict requirements for the appearance of printed boards. Solder resist is like the "coat" of printed boards. In addition to having a certain thickness and hardness, solvent resistance tests, and adhesion tests that meet standards, it also requires a uniform surface color, a glossy finish (currently, the brighter the better in domestic guest rooms), no garbage, and no excess marks on the surface. It can be said that the appearance quality of solder resist is not only a reflection of a company's technical and management level, but also directly affects the company's "orders". Therefore, how to improve the appearance quality of solder resist for printed boards has become a problem that every printed board factory needs to solve. Based on my practical experience, I will discuss how to improve the appearance quality of solder mask from four aspects: screen printing, exposure, development, and post curing.
II. Factors affecting the appearance quality of solder resist
1. Silk screen printing:
During the screen printing process of photosensitive solder mask, the flatness of the scraper, the cleanliness of the screen printing environment, the use of screen sealing tape and ink preparation during screen printing, screen printing pressure, and the brush plate before screen printing can all affect the appearance quality. According to the actual production situation, the top three factors have the greatest impact. The uneven scraper can easily create scraper marks on the surface of the solder mask; Insufficient cleanliness in the screen printing room can easily generate garbage on the surface of the solder mask; Improper use of sealing tape can easily cause surface adhesive to dissolve in the solvent of the ink.
2. Exposure:
During the exposure process of solder mask ink, due to the incomplete solidification of the solder mask, it is easy to produce imprints when the solder mask film adheres to the solder mask, which is the main reason for affecting the appearance quality of the solder mask.
3. Development:
At present, the development of solder resist ink is generally carried out using a horizontal conveyor type. Due to the incomplete solidification of solder resist, the driving and pressing wheels of the development machine can easily cause damage to their surface, resulting in roller marks and affecting the appearance quality of solder resist. In addition, incorrect exposure energy can also affect the glossiness of the solder resist, but this can be controlled through a light wedge table.
4. Post curing
Uneven temperature during post curing of solder mask can easily cause uneven color of solder mask. When the temperature is too high, it can even cause local yellowing and blackening, affecting the appearance of solder mask.
Improve the appearance quality of solder resist from four aspects
1. Silk screen printing:
When using silk screen solder resist ink, due to the uneven surface of the silk screen, after a period of silk screen printing, the surface of the scraper will become uneven, leaving a scraper mark on the solder resist surface. Therefore, the operator must pay attention to the surface condition at all times. Once any scratches are found, the scraper should be immediately reground to ensure its flatness.
We conducted parallel experiments to address the issue of surface adhesive particles on solder resist. Select two different types of tape for screen sealing, use two types of solder resist ink for screen printing, and observe the condition of surface adhesive particles, as shown in Table 1.
From the above experimental results, it can be seen that tape A has a good combination effect with ink B, while tape B has a good combination effect with both ink A and ink B
