Electro- and electroless plating of tin, nickel, gold, and solder are common surface treatments for flexible circuits. Solder plating via hot-air leveling could offer a cost-effective solution. However, it involves severe high-temperature processing conditions, and the resulting solder uniformity is often inadequate for many applications.
Several new surface finishing technologies have been developed to meet the demands of emerging termination technologies. Soft nickel/gold plating is primarily used in wire bonding and flip-chip bonding processes. Tin plating is also available for flip-chip bonding. Hard nickel/gold plating is applied to fine-pitch pads for ACF termination (Anisotropic Conductive Film) and insertion parts of FFC connectors. Tin- and lead-free solder plating serves as an alternative to traditional solder plating. OSP (Organic Surface Protection) presents a cost-effective solution for next-generation soldering, eliminating lead components.
Before applying surface treatments to exposed conductors, a suitable cleaning process is crucial to ensure optimal plating performance. This often requires a robust chemical cleaner with mechanical brushing to remove tough residues and oxidation from the copper surface left by previous processes. Strong alkaline solutions should be avoided as cleaning agents, as they can adversely affect several adhesive resins and photo-imageable coverlays, leading to delamination of the coverlay.
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Image 1: Flexible Circuit Manufacturing
Electroplating provides a reliable metallic surface treatment, controlling thickness and surface conditions effectively. Managing the plated metal surface to be shiny or non-shiny is not difficult. However, a critical issue arises with ensuring all metal pads are connected to the electrodes. This is straightforward for simple cable-type flexible circuits with predominantly parallel lines. Yet, it becomes a significant challenge for SMT-type circuits with electrically isolated termination pads. These require additional trace lines solely for electroplating, which are subsequently cut after processing.
Electroless plating offers fewer restrictions in its application. It deposits plated metals uniformly on all exposed terminals, even those that are electrically isolated. However, the electroless plating process faces limitations in controlling metal thickness and quality. Its extended processing time and the high cost of solutions contribute to the expense of thick plating. Essentially, electroless plating involves chemical reactions in an aqueous solution.
Certain plating solutions, particularly high-pH alkaline ones, can cause significant damage to adhesive layers and coverlay materials. Micro bump arrays are constructed using advanced processes. Optimized combinations of plating techniques can create various bump shapes cost-effectively.
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I adjusted the wording to improve clarity and flow while maintaining the technical details of the original text.
Image 2: FPC Flexible Circuit Surface
Flexible circuits incorporate various supplementary structures beyond electrical traces to enhance their functionality. Among these, stiffener boards play a pivotal role. However, automating the production of stiffener boards proves challenging due to their diverse configurations. As a result, most processes still rely on manual labor, contributing significantly to manufacturing costs.
Typically, an adhesive film is initially laminated onto a rigid board with a release sheet. Subsequently, the boards undergo routing either through punching or using an NC router.
For pressure-sensitive adhesive materials (PSAs), the application process is relatively straightforward. Each stiffener piece is manually placed onto the flex circuits with appropriate pressure.
In contrast, thermo-set adhesive materials necessitate a more complex procedure. This involves subjecting the assembly to temperatures exceeding 160°C and pressures above 20 kg/cm² for over 30 minutes. Specialized equipment such as a heat press, akin to those used for multilayer circuit boards or film coverlays, becomes essential. Dummy boards are employed to ensure uniform pressure distribution. Alternatively, a heat press equipped with a vacuum chamber or an autoclave can ensure consistent adhesion, especially for irregularly shaped stiffener boards.
1 Image 3: SUS stiffener for flexible circuit
Several new surface finishing technologies have been developed to meet the demands of emerging termination technologies. Soft nickel/gold plating is primarily used in wire bonding and flip-chip bonding processes. Tin plating is also available for flip-chip bonding. Hard nickel/gold plating is applied to fine-pitch pads for ACF termination (Anisotropic Conductive Film) and insertion parts of FFC connectors. Tin- and lead-free solder plating serves as an alternative to traditional solder plating. OSP (Organic Surface Protection) presents a cost-effective solution for next-generation soldering, eliminating lead components.
Before applying surface treatments to exposed conductors, a suitable cleaning process is crucial to ensure optimal plating performance. This often requires a robust chemical cleaner with mechanical brushing to remove tough residues and oxidation from the copper surface left by previous processes. Strong alkaline solutions should be avoided as cleaning agents, as they can adversely affect several adhesive resins and photo-imageable coverlays, leading to delamination of the coverlay.
—
Image 1: Flexible Circuit Manufacturing
Electroplating provides a reliable metallic surface treatment, controlling thickness and surface conditions effectively. Managing the plated metal surface to be shiny or non-shiny is not difficult. However, a critical issue arises with ensuring all metal pads are connected to the electrodes. This is straightforward for simple cable-type flexible circuits with predominantly parallel lines. Yet, it becomes a significant challenge for SMT-type circuits with electrically isolated termination pads. These require additional trace lines solely for electroplating, which are subsequently cut after processing.
Electroless plating offers fewer restrictions in its application. It deposits plated metals uniformly on all exposed terminals, even those that are electrically isolated. However, the electroless plating process faces limitations in controlling metal thickness and quality. Its extended processing time and the high cost of solutions contribute to the expense of thick plating. Essentially, electroless plating involves chemical reactions in an aqueous solution.
Certain plating solutions, particularly high-pH alkaline ones, can cause significant damage to adhesive layers and coverlay materials. Micro bump arrays are constructed using advanced processes. Optimized combinations of plating techniques can create various bump shapes cost-effectively.
—
I adjusted the wording to improve clarity and flow while maintaining the technical details of the original text.
Image 2: FPC Flexible Circuit Surface
Flexible circuits incorporate various supplementary structures beyond electrical traces to enhance their functionality. Among these, stiffener boards play a pivotal role. However, automating the production of stiffener boards proves challenging due to their diverse configurations. As a result, most processes still rely on manual labor, contributing significantly to manufacturing costs.
Typically, an adhesive film is initially laminated onto a rigid board with a release sheet. Subsequently, the boards undergo routing either through punching or using an NC router.
For pressure-sensitive adhesive materials (PSAs), the application process is relatively straightforward. Each stiffener piece is manually placed onto the flex circuits with appropriate pressure.
In contrast, thermo-set adhesive materials necessitate a more complex procedure. This involves subjecting the assembly to temperatures exceeding 160°C and pressures above 20 kg/cm² for over 30 minutes. Specialized equipment such as a heat press, akin to those used for multilayer circuit boards or film coverlays, becomes essential. Dummy boards are employed to ensure uniform pressure distribution. Alternatively, a heat press equipped with a vacuum chamber or an autoclave can ensure consistent adhesion, especially for irregularly shaped stiffener boards.
1 Image 3: SUS stiffener for flexible circuit
