Method for improving surface treatment skip plating of precision bonding pad

Abstract

The invention belongs to the technical field of printed circuit board manufacturing, and particularly relates to a method for improving surface treatment skip plating of a precision bonding pad, which comprises the following steps of: constructing a nano catalytic anchor point layer on the surface of the precision bonding pad to be electroplated; and at the initial stage of electroplating, applying a non-constant electric field pulse sequence to the bonding pad constructed with the nano-catalysis anchor point layer so as to guide metal ions to realize directional deposition on the nano-catalysis anchor point layer. According to the invention, the high-activity nano-catalysis anchor point layer is constructed, and the strong electric field pulse is combined to actively guide the metal deposition, so that the complete coverage of the bonding pad can be realized even in the presence of a trace amount of insulating material.

Description

Technical Field

[0001] This invention belongs to the field of printed circuit board manufacturing technology, and specifically relates to a method for improving the surface treatment of precision solder pads by skip plating. Background Technology

[0002] As electronic devices become smaller and denser, the size and spacing of solder pads on printed circuit boards are constantly shrinking. When performing electroplating surface treatment on such precision solder pads, the phenomenon of "skip plating" is very likely to occur, meaning that the target metal layer is not deposited on the solder pad in parts or all of them.

[0003] The root cause of plating skips lies in the presence of a microscopic insulating layer on the solder pad surface, which hinders the initiation of the electrochemical reaction. These insulating layers include:

[0004] 1. Organic contaminants: such as solder resist ink residue, operator grease, etc.

[0005] 2. Inorganic oxide layer: Copper oxide formed on the copper surface during processing or storage.

[0006] 3. Inherent defects in the substrate: such as "resin depressions" generated during the lamination process, which cause insulating resin to cover the copper foil.

[0007] Current technologies primarily address this issue by enhancing cleaning, optimizing solder resist processes, and adjusting electroplating parameters. However, these methods are all "passive defenses" and cannot completely resolve nanoscale contamination and inherent defects.

[0008] In view of this, the present invention provides a method for improving the surface treatment of precision solder pads to solve the above problems. Summary of the Invention

[0009] To achieve the above objectives, the present invention provides the following technical solution: a method for improving the surface treatment of precision solder pads by skipping plating, comprising the following steps:

[0010] A nano-catalytic anchor layer is constructed on the surface of the precision solder pad to be electroplated;

[0011] In the initial stage of electroplating, a non-constant electric field pulse sequence is applied to the pads on which the nanocatalytic anchor layer is constructed to guide the directional deposition of metal ions on the nanocatalytic anchor layer.

[0012] As a preferred embodiment of the method for improving the surface treatment of precision solder pads in electroplating according to the present invention, the steps of the nano-catalytic anchor layer include: performing plasma activation treatment on the solder pad surface to clean the surface and increase surface activity; constructing a molecular bridging layer on the activated surface; fixing noble metal ions through the molecular bridging layer and reducing them to noble metal nanoparticles in the electroplating environment, thereby forming the nano-catalytic anchor layer.

[0013] As a preferred embodiment of the method for improving the surface treatment of precision solder pads by skip plating according to the present invention, the gas used in the plasma activation treatment is a mixed gas containing inert gas and oxygen, with a volume ratio of 3-5:1.

[0014] As a preferred embodiment of the method for improving the surface treatment of precision solder pads in this invention, the molecular bridging layer is composed of an aminosilane coupling agent; the aminosilane coupling agent forms a covalent bond with the solder pad surface through its siloxane end, and chelates noble metal ions through its amino end.

[0015] In a preferred embodiment of the method for improving the surface treatment of precision solder pads using skip plating according to the present invention, the noble metal ion is palladium ion, and the noble metal nanoparticle is palladium nanoparticle.

[0016] As a preferred embodiment of the method for improving the surface treatment of precision pads by skip plating according to the present invention, the electric field pulse sequence includes at least one positive pulse with high current density and at least one reverse pulse with low current density.

[0017] In a preferred embodiment of the method for improving the surface treatment of precision solder pads by skip plating according to the present invention, the current density of the positive pulse is 2-5 times the electroplating current density, and the pulse width is 20-100 milliseconds.

[0018] In a preferred embodiment of the method for improving the surface treatment of precision solder pads by skip plating according to the present invention, the current density of the reverse pulse is 10%-50% of the current density of the forward pulse, and the pulse width is 5-20 milliseconds.

[0019] As a preferred method for improving the surface treatment of precision pads by skip plating according to the present invention, the electric field pulse sequence comprises 2-5 cycles consisting of the positive pulse and the reverse pulse.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] This invention constructs a highly active nanocatalytic anchor layer and combines it with a strong electric field pulse to actively guide metal deposition, ensuring complete coverage of the pads even in the presence of trace amounts of insulating material. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] This invention relates to a method for improving the surface treatment of precision solder pads during electroplating, comprising: constructing a nano-catalytic anchor layer on the surface of the precision solder pad to be electroplated; and in the initial stage of electroplating, applying a non-constant electric field pulse sequence to the solder pad with the nano-catalytic anchor layer to guide the directional deposition of metal ions on the nano-catalytic anchor layer.

[0024] Specifically: First, a mixture of inert gas and oxygen is used to bombard and clean the surface of the solder pads, thoroughly removing contaminants while forming an active oxide surface and micro-anchor points.

[0025] In this step, the mixed gas is a mixture of argon and oxygen in a ratio of 3-5:1. The specific principle is as follows: Argon, as an inert gas, uses plasma primarily through physical bombardment (ion bombardment) to extremely effectively remove organic contaminants and metal oxides several atomic layers from the solder pad surface, achieving atomic-level cleanliness. Simultaneously, this bombardment generates numerous dangling bonds and microscopic defects on the copper surface, forming attachment anchors. Meanwhile, the oxygen plasma has a strong chemical oxidation effect, decomposing residual organic contaminants and converting them into volatile CO2 and H2O that are then removed. Furthermore, it forms an extremely thin but dense and uniform copper oxide layer on the copper surface. This oxide layer serves as a "reaction platform" for chemical bonding with the silane coupling agent.

[0026] Then, an aminosilane coupling agent is used to form a molecular bridging layer on the surface of the activated pad. One end of the coupling agent is covalently bonded to the copper surface, and the other end provides chelation sites for metal ions. The treated pad is then immersed in an activation solution containing palladium ions, so that the palladium ions are chelated on the molecular bridging layer. When it enters the electroplating solution in the future, these palladium ions are reduced in situ to highly catalytically active palladium nanoparticles, forming a nanocatalytic anchor layer.

[0027] The specific principle of this step is as follows: The aminosilane coupling agent is a bifunctional molecule. The siloxane group (-SiOR) at one end will undergo a hydrolysis-condensation reaction with the thin copper oxide layer formed in step one to form a strong Si-O-Cu covalent bond; the amino group (-NH2) at the other end faces outward and serves as a strong metal ion chelating site to build a molecular-level, strong molecular bridging layer rich in active sites on the copper surface. This membrane is hydrophilic and positively charged, and can efficiently adsorb noble metal anions in subsequent steps.

[0028] The activation solution contains palladium chloride (PdCl2) and a mild stabilizer, in which Pd... 2+The ions are strongly and selectively chelated and fixed by the amino groups (-NH2) on the silane layer, and uniformly adsorbed across the entire pad surface. When the board enters the electroplating bath, the initial current and solution environment in the electroplating solution will in situ transfer these adsorbed Pd ions to the pads. 2+ The process reduces the material to highly catalytically active palladium (Pd) nanoparticles. These palladium nanoparticles provide numerous low-potential, highly active electrochemical nucleation sites, significantly reducing the activation energy required for metal deposition. Furthermore, they act as conductive bridges, ensuring a conductive path for current even on substrates with nanoscale insulating films, thus guaranteeing the stability of the electroplating process.

[0029] Finally, in the initial stage of electroplating, a composite electrical signal containing a high current density forward pulse and a short reverse pulse is applied to drive metal ions to rapidly and uniformly nucleate and grow on the nanocatalytic anchor layer, forming a complete initial coating.

[0030] The specific principle behind this step is as follows: the strong electric field and high overpotential of a high-density positive pulse can drive a large number of metal ions (such as Ni) 2+ Or Au + The metal rushes towards the nano-catalytic anchor layer and preferentially and rapidly and densely reduces and nucleates on these active sites, instantly forming a continuous and completely covered initial metal film, thereby completely eliminating skip-plating.

[0031] The short reverse pulse dissolves the deposits that may form under high peak current, leaving only the densest and best-bonded core crystal nuclei, thus ensuring the quality and smoothness of the initial coating and improving the quality of subsequent electroplating.

[0032] Example 1:

[0033] The following explanation uses the production of HDI boards as an example:

[0034] A batch of HDI boards with completed pattern transfer, etching, and solder mask fabrication were selected, with a minimum pad diameter of 50μm. These boards underwent acid degreasing, micro-etching (controlling copper thickness reduction by 1.0μm), and sulfuric acid activation, and were used as samples for further processing.

[0035] The sample was placed in a vacuum plasma apparatus and a mixture of argon and oxygen (volume ratio 3:1) was introduced. It was processed for 2 minutes under a vacuum of 100 Pa and a power of 500 W.

[0036] Immediately immerse the treated sample in a 1.5 wt% aqueous solution of γ-aminopropyltriethoxysilane for 3 minutes. After removal, gently rinse with deionized water for 30 seconds and then cure in an 80°C oven for 5 minutes.

[0037] After curing, the sample was immersed in a 50 mg / L palladium chloride activation solution (pH=5.0) for 5 minutes. After removal, it was thoroughly rinsed with deionized water and dried with hot air. At this point, palladium ions were firmly chelated onto the molecular bridging layer.

[0038] Finally, the sample is placed into the selective gold plating fixture. During the initial electroplating stage, a three-cycle pulse sequence is applied: a forward pulse (current density 5 ASD, pulse width 50 ms) followed by a reverse pulse (current density 1.5 ASD, pulse width 10 ms). Immediately after the pulse sequence, the process is switched to conventional DC electroplating (current density 1 ASD, time 30 min).

[0039] Example 2:

[0040] Let's take the production of IC substrates as an example for a specific explanation:

[0041] A batch of IC substrates with a high risk of resin depression was selected, showing obvious micro-depressions on the pad surfaces. After standard pretreatment cleaning, they were put into use.

[0042] A milder plasma parameter was used: an argon / oxygen mixed gas (volume ratio 5:1), a vacuum of 80 Pa, a power of 300 W, and a treatment time of 3 minutes. The mixture was then soaked in an aminosilane coupling agent solution with a concentration of 1.0 wt% for 4 minutes. The subsequent rinsing and curing steps were the same as in Example 1.

[0043] A lower concentration but longer immersion time (palladium chloride 30 mg / L, immersion 8 minutes) was used to ensure sufficient adsorption on complex surfaces and resin depressions. The initial electroplating pulse sequence was adjusted to: a forward pulse (current density 4 ASD, pulse width 80 ms) followed by a reverse pulse (current density 1 ASD, pulse width 15 ms), cycled twice. Normal electroplating was then performed afterward.

[0044] Comparative Example 1:

[0045] HDI boards from the same batch as those used in the example were selected, and a standard industry-standard plating improvement solution was adopted:

[0046] Two high-intensity chemical cleaning processes are performed first to increase the amount of micro-etching (controlling the copper thickness to be reduced by 1.5μm) before electroplating.

[0047] Comparative Example 2:

[0048] Take HDI boards from the same batch as those in the example and follow the procedure below:

[0049] First, plasma activation was performed in the same manner as in Example 1, but the steps of constructing the molecular bridging layer and fixing the nanocatalytic anchor layer were omitted. Then, the electric field-assisted directional deposition and subsequent electroplating were performed directly in the same manner as in Example 1.

[0050] The test results are shown in Table 1 below:

[0051] Table 1

[0052] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving the surface treatment of precision solder pads by skipped plating, characterized in that, Includes the following steps: A nano-catalytic anchor layer is constructed on the surface of the precision solder pad to be electroplated; In the initial stage of electroplating, a non-constant electric field pulse sequence is applied to the pads on which the nanocatalytic anchor layer is constructed to guide the directional deposition of metal ions on the nanocatalytic anchor layer.

2. The method for improving the surface treatment of precision solder pads by skipped plating according to claim 1, characterized in that: The steps of the nanocatalytic anchor layer include: performing plasma activation treatment on the surface of the pad to clean the surface and increase surface activity; constructing a molecular bridging layer on the activated surface; fixing noble metal ions through the molecular bridging layer and reducing them to noble metal nanoparticles in an electroplating environment, thereby forming the nanocatalytic anchor layer.

3. The method for improving the surface treatment of precision solder pads by skipped plating according to claim 2, characterized in that: The gas used in the plasma activation treatment is a mixture of inert gas and oxygen in a volume ratio of 3-5:

1.

4. The method for improving the surface treatment of precision solder pads by skipped plating according to claim 2, characterized in that: The molecular bridging layer is composed of an aminosilane coupling agent; the aminosilane coupling agent forms covalent bonds with the pad surface through its siloxane end and chelates noble metal ions through its amino end.

5. The method for improving the surface treatment of precision solder pads by skipped plating according to claim 2, characterized in that: The noble metal ion is palladium ion, and the noble metal nanoparticle is palladium nanoparticle.

6. The method for improving the surface treatment of precision solder pads by skipped plating according to claim 1, characterized in that: The electric field pulse sequence includes at least one positive pulse with high current density and at least one reverse pulse with low current density.

7. The method for improving the surface treatment of precision solder pads by skipped plating according to claim 6, characterized in that: The current density of the positive pulse is 2-5 times that of the electroplating current density, and the pulse width is 20-100 milliseconds.

8. The method for improving the surface treatment of precision solder pads by skipped plating according to claim 7, characterized in that: The current density of the reverse pulse is 10%-50% of the current density of the forward pulse, and the pulse width is 5-20 milliseconds.

9. The method for improving the surface treatment of precision solder pads by skipped plating according to claim 6, characterized in that: The electric field pulse sequence comprises 2-5 cycles consisting of the positive pulse and the negative pulse.

Images