Abstract: This article explores the use of peelable adhesives as an alternative to special tapes for protecting gold plating and hot air leveling, and investigates the application of the peelable adhesive process in PCB production.
I. Introduction
Pin gold plating and hot air leveling are crucial processes in printed circuit board manufacturing, necessitating protection for areas that do not require processing. Traditionally, special adhesive tapes have been employed as protective layers during plating and hot air leveling. However, this approach has drawbacks, including high costs, lengthy production cycles (especially for mass production), and adhesive residue that detracts from the board’s appearance.
Currently, some coastal PCB companies have adopted peelable adhesives instead of tapes, achieving similar protective benefits during gold plating and hot air leveling. Additionally, peelable adhesives offer several advantages: significantly reduced costs, straightforward application, no residual marks or stains, and ease of use in mass production. In the printed circuit board industry, cost efficiency is a priority, making the potential for peelable adhesives highly promising.
2. Characteristics of Peelable Glue
Peelable glue is a one-component screen printing protective ink, consisting of 100% solid content and appearing as a blue, viscous liquid. It serves as a protective layer during electroplating, safeguarding non-plated circuit sections and solder leads. The primary function of peelable glue is to act as a temporary protective layer, replacing traditional tape, and it must be completely removed after use.
3. Operational Points
To facilitate easier peeling, the printed circuit board should be thoroughly cleaned before application to eliminate grease and contaminants, using a specialized cleaning agent. Due to its viscosity, peelable glue is typically applied via screen printing, utilizing a mesh size below 18T and a 60-degree rounded polyurethane squeegee. This ensures the glue achieves an appropriate thickness for effective peeling. Generally, no thinner is added during application. To achieve the desired thickness, the doctor blade angle should be maintained between 45-55 degrees. For optimal masking, the cutting speed must be slower than usual; otherwise, adequate protection may not be attained.
The coating process should ensure that the peelable glue is evenly distributed on the board’s surface, with a specific thickness. The glue should flow into the holes to a depth of two-thirds to one-third; care must be taken to prevent it from flowing into the opposite side, which could create “rivets” that complicate peeling.
The drying and curing process significantly impacts peeling performance. Typically, curing occurs in a hot air circulating oven at 140°C for 20-30 minutes. After curing, the peelable adhesive should exhibit high internal stress and elasticity. Achieving the ideal peeling effect requires avoiding both over-curing and under-curing.
4. Conclusion
Extensive experimentation has demonstrated that the performance of peelable adhesive is highly stable, with strong adhesion to solder masks. To address peeling difficulties, we modified the PCB screen printing technique, utilized various mesh screens, employed different hardness squeegees, and adjusted curing times, leading to notable improvements in peeling effectiveness.
During the gold-plating of pins, the peelable glue effectively protects holes and areas that do not require electroplating, preventing the gold plating solution from penetrating. Additionally, it safeguards gold-plated pins during the hot air leveling process of PCBs, showing no signs of adhesive failure at high temperatures. There was also no tin or lead adherence to the gold pins, indicating that the peelable glue withstands elevated temperatures. Compared to specialized protective tape, the peelable adhesive significantly reduces costs while maintaining excellent performance, resulting in widespread application.
I. Introduction
Pin gold plating and hot air leveling are crucial processes in printed circuit board manufacturing, necessitating protection for areas that do not require processing. Traditionally, special adhesive tapes have been employed as protective layers during plating and hot air leveling. However, this approach has drawbacks, including high costs, lengthy production cycles (especially for mass production), and adhesive residue that detracts from the board’s appearance.
Currently, some coastal PCB companies have adopted peelable adhesives instead of tapes, achieving similar protective benefits during gold plating and hot air leveling. Additionally, peelable adhesives offer several advantages: significantly reduced costs, straightforward application, no residual marks or stains, and ease of use in mass production. In the printed circuit board industry, cost efficiency is a priority, making the potential for peelable adhesives highly promising.
2. Characteristics of Peelable Glue
Peelable glue is a one-component screen printing protective ink, consisting of 100% solid content and appearing as a blue, viscous liquid. It serves as a protective layer during electroplating, safeguarding non-plated circuit sections and solder leads. The primary function of peelable glue is to act as a temporary protective layer, replacing traditional tape, and it must be completely removed after use.
3. Operational Points
To facilitate easier peeling, the printed circuit board should be thoroughly cleaned before application to eliminate grease and contaminants, using a specialized cleaning agent. Due to its viscosity, peelable glue is typically applied via screen printing, utilizing a mesh size below 18T and a 60-degree rounded polyurethane squeegee. This ensures the glue achieves an appropriate thickness for effective peeling. Generally, no thinner is added during application. To achieve the desired thickness, the doctor blade angle should be maintained between 45-55 degrees. For optimal masking, the cutting speed must be slower than usual; otherwise, adequate protection may not be attained.
The coating process should ensure that the peelable glue is evenly distributed on the board’s surface, with a specific thickness. The glue should flow into the holes to a depth of two-thirds to one-third; care must be taken to prevent it from flowing into the opposite side, which could create “rivets” that complicate peeling.
The drying and curing process significantly impacts peeling performance. Typically, curing occurs in a hot air circulating oven at 140°C for 20-30 minutes. After curing, the peelable adhesive should exhibit high internal stress and elasticity. Achieving the ideal peeling effect requires avoiding both over-curing and under-curing.
4. Conclusion
Extensive experimentation has demonstrated that the performance of peelable adhesive is highly stable, with strong adhesion to solder masks. To address peeling difficulties, we modified the PCB screen printing technique, utilized various mesh screens, employed different hardness squeegees, and adjusted curing times, leading to notable improvements in peeling effectiveness.
During the gold-plating of pins, the peelable glue effectively protects holes and areas that do not require electroplating, preventing the gold plating solution from penetrating. Additionally, it safeguards gold-plated pins during the hot air leveling process of PCBs, showing no signs of adhesive failure at high temperatures. There was also no tin or lead adherence to the gold pins, indicating that the peelable glue withstands elevated temperatures. Compared to specialized protective tape, the peelable adhesive significantly reduces costs while maintaining excellent performance, resulting in widespread application.
