Discussion on hole metallization process of the ho

2022-07-23
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As we all know, hole metallization is the most critical link in the production process of multilayer boards, and it is related to the internal quality of multilayer boards. The process of hole metallization can be divided into two processes, namely, removing drilling contamination and chemical copper deposition. Chemical copper deposition is a process of interconnecting inner and outer circuits; The function of removing drilling dirt is to remove the epoxy resin drilling dirt (especially on the copper ring) caused by high temperature during high-speed drilling, so as to ensure the high reliability of circuit connection after chemical copper deposition. 2、 The process of hole metallized multilayer plate can be divided into concave etching process and non concave etching process. At the same time, the epoxy resin and glass fiber should be removed to form a reliable three-dimensional bond; The non pitting process only removes the epoxy drilling dirt that falls off and vaporizes during the drilling process to obtain a clean hole wall and form a two-dimensional combination. Theoretically speaking, the three-dimensional combination is more reliable than the two-dimensional combination, but the corresponding technical requirements can be fully met by improving the compactness and ductility of the chemical copper deposition layer. The non concave etching process is simple, reliable and mature, so it is widely used in most manufacturers. Potassium permanganate is a typical non pitting process. 2.1 process flow epoxy swelling → secondary countercurrent rinsing → potassium permanganate de drilling → secondary countercurrent rinsing → neutralization and reduction → secondary countercurrent rinsing → adjustment → secondary countercurrent rinsing → roughening → secondary countercurrent rinsing → prepreg → ionic palladium activation → secondary countercurrent rinsing → reduction → water washing → chemical copper precipitation → secondary countercurrent rinsing → prepreg acid → pre copper plating 2.2 process principle and control 2.2.1 swelling purpose: swelling epoxy resin to soften it, Prepare for potassium permanganate to remove drilling dirt

formula: NaOH 20g/l

hexanediol ether 30/l

hexanediol 2g/l

water the rest

temperature ℃

time 5min epoxy resin is a highly polymeric compound with excellent corrosion resistance. Its corrosion forms mainly include dissolution, swelling and chemical cracking (for example, concentrated sulfuric acid mainly dissolves epoxy resin, and its pitting effect is very obvious). According to the empirical rule of "similar miscibility", ether organics generally have weak polarity and have a molecular structure (r-o-r') similar to epoxy resin, so they have a certain solubility in epoxy resin. Because ether can associate with water by hydrogen bond, it has certain solubility in water. Therefore, water-soluble ether organics are commonly used as swelling agents for drilling. The content of sodium hydroxide in the swelling solution should not be too high, otherwise, it will destroy the hydrogen bond association of copper and copper products, which is the characteristic industry of Tongling City, making the organic chain phase separate. In production, this method is often used to analyze the content of swelling agent. 2.2.2 decontamination purpose: use the strong oxidation of potassium permanganate to oxidize and crack the swelling and softening epoxy resin drilling dirt

formula: NaOH 35g/l

kmno4 55g/l

nacio 0.5g/l

temperature 75 ℃

time 10min potassium permanganate is a strong oxidant. In strong acid solution, it reacts with reductant and is reduced to mn2+; In neutral and weak alkaline environment, it is reduced to MnO2; When the NaOH concentration is greater than 2mol/l, it is reduced to mno42-. Potassium permanganate has higher and stronger oxidizability in strong acidic environment due to early solidification of gate, but the reaction speed of oxidizing organic matter under alkaline condition is faster than that under acidic condition. Under high temperature alkaline conditions, potassium permanganate oxidizes and breaks the carbon chain of epoxy resin:

4mno4-+c epoxy resin +40h- = 4mno42-+co2 (g) +2h2o ①

at the same time, The following side reactions of potassium permanganate occur:

4mno4- +40h- = 4mno42- + O2 (g) + 2H2O ②

mno42- the following side reactions also occur in alkaline medium:

mno42- + 2H2O + 2e-- tanghuyu (technician) = MnO2 (s) + 40h- ③

nacio is used as the regenerant of potassium permanganate, mainly to oxidize mno42- to mno4-. 2.2.3 reduction purpose: remove the residual potassium permanganate, potassium manganate and manganese dioxide from potassium permanganate to remove drilling dirt

formula:

h2so4 100ml/l

nac2o4 30g/l

manganese ion at 40 ℃ is a heavy metal ion, and its existence will cause "palladium poisoning", making palladium ion or protons lose activation activity, resulting in the failure of pore metallization. Therefore, manganese must be removed before chemical precipitation of copper. In acid medium:

3mno42-+4h+ = 2mno4-+mno2 (s) +2h2o ④

2mno4-+5c2o42-+16h+ = 2mn2++10co2 (g) +8h2o5 ⑤

c2o42-+mno2+4h+ = mn2+2co2+2h2o ⑥ it can be seen from the above reactions that potassium permanganate can be completely removed through the reduction steps to remove the residual potassium permanganate, potassium manganate and manganese dioxide. In relevant data, hydrazine compounds and other strong reducing substances are also used for reduction treatment, which is mainly used to treat residual Cr6 + in plastic electroplating, and has certain effect. However, the role of manganese dioxide needs to be discussed, so it is necessary to avoid the formation of manganese dioxide as much as possible. 2.2.4 adjustment purpose: adjust pore wall charge

formula: anionic surfactant 0 To achieve a reasonable matching of advanced battery materials, 5g/l. In order to make the epoxy resin surface adsorb uniform palladium ions in the post-processing, the printed board must be added into the anionic surfactant to make its surface adsorb a layer of uniform negative organic film. 2.2.5 roughening purpose:

a. remove the organic film on the copper surface

b. micro coarsening copper surface. Formula:

h2so4 100ml/l

h2o2 80ml/l

nh2ch2nh2 10g/l adjustment treatment, adsorb organic surfactant on epoxy resin

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