Main processing technology and production equipment of DPC ceramic substrate
DPC ceramic substrates have the characteristics of high line accuracy, high surface flatness, high insulation and high thermal conductivity. They have quickly occupied an important market position in the field of semiconductor power device packaging and are widely used in high-power LEDs, semiconductor lasers, VCSELs and other fields.
DPC ceramic substrates have the characteristics of high line accuracy, high surface flatness, high insulation and high thermal conductivity. They have quickly occupied an important market position in the field of semiconductor power device packaging and are widely used in high-power LEDs, semiconductor lasers, VCSELs and other fields.
Direct Plating Copper (DPC) is a ceramic circuit processing technology developed on the basis of ceramic thin film processing. The process first uses vacuum coating to sputter the copper-metal composite layer on the ceramic substrate, then uses yellow light lithography to repeatedly expose, develop, etch, and remove the film to complete the circuit production, and finally uses electroplating/chemical plating deposition to increase the thickness of the circuit. After the photoresist is removed, the metallized circuit production is completed.
DPC ceramic substrates are small in size, precise in structure, high in reliability requirements, complex in process flow, and delicate in production process. They are technology-intensive industries with high technical barriers. Its production process mainly involves drilling, magnetron sputtering, chemical copper deposition, electroplating copper, solder mask printing, chemical silver deposition/chemical gold deposition and other major processes.
1. Laser drilling
Before laser drilling, first apply a layer of water-soluble food-grade substrate pigment on the ceramic substrate with a brush to reduce the reflectivity of the laser on the substrate and enhance the laser drilling effect. Place it in a drying oven for drying, and then use a laser drilling machine to open up the upper and lower substrates as a path for connecting the upper and lower panels.
Drilling holes with laser drilling machines will use infrared, green, ultraviolet, CO2 and other laser beams of different wavelengths to irradiate the surface of the material for different ceramic materials. Each time a laser pulse is emitted, a part of the material is burned off.
2. Laser coding
Laser coding is the process of using a laser coding machine to engrave a product QR code onto a substrate.
3. Ultrasonic cleaning
Cleaning removes the red glue attached to the substrate after laser drilling and laser coding, and trace particles generated by coding, to ensure the cleanliness of the board surface, and removes the burrs generated by drilling through rough scraping, bubbling, and fine scraping. After scraping, wash with water to rinse off the particles attached to the surface of the substrate. The substrate after slag removal needs to be micro-etched to roughen the surface, to improve the effect of magnetron sputtering in the later process, and then dried to remove moisture from the surface of the substrate.
4. Magnetron sputtering
The basic principle of magnetron sputtering is to inject a small amount of argon gas into a high vacuum sealed high voltage electric field container to ionize the argon gas and generate an argon ion flow to bombard the target cathode in the container. The target material atoms are squeezed out one by one, and the molecules are precipitated and accumulated on the ceramic substrate to form a thin film.
Before sputtering, in order to achieve good results, it must be pre-treated by dust removal, oil removal, slow pulling, etc.
5. Chemical copper deposition
The main purpose of chemical copper deposition is to thicken the copper layer and increase the conductivity of the via, while ensuring better connectivity with the sputtered copper layer. Chemical copper plating is a catalytic redox reaction. Because the mechanical properties of the copper layer of chemical copper plating are poor and it is easy to break when subjected to impact, chemical copper plating should adopt thin copper plating process.
Chemical copper plating must go through pre-treatment processes including degreasing, micro-etching, pre-immersion, activation, and promotion.
6. Full-board electroplating
The function of full-board electroplating, that is, pre-electroplating copper, is mainly to increase the thickness of the copper layer, mainly including degreasing, micro-etching, pickling, copper plating, and stripping (hanging) processes. Electroplating copper uses copper balls as anodes, CuSO4 and H2SO4 as electrolytes, and the main chemical reaction formulas of copper plating are represented by the following cathode chemical reaction formulas: Cu2+ +2e- →Cu. After the pre-copper plating is completed, the excess copper layer on the fixture needs to be stripped off.
7. Grinding-Laminating-Exposure-Development
After the copper layer is electroplated on the entire board, it is necessary to engrave the circuit on the copper surface of the substrate to prepare for the next process of thickening the copper layer of the circuit. The process mainly includes pickling, grinding, laminating, exposure, and development.
1) Pickling: Use 3~5% sulfuric acid solution to clean the surface of the substrate to remove the oxide film that may exist on the surface of the substrate.
2) Grinding: Use the grinding wheel of the grinding machine to roughen the surface of the substrate, clean and brighten the surface of the substrate, and remove fingerprints, grease, etc. attached to the surface of the substrate;
3) Lamination: Apply the photosensitive liquid to the polyester film base in advance, dry it to form a photosensitive layer, and then cover it with a layer of polyethylene film. This three-layer photosensitive resist material is called dry film resist, or dry film for short;
4) Exposure: Place the film on the dry film laminated on the substrate, and use the film imaging principle. The exposure machine generates ultraviolet light to polymerize the film on the chrome plate to form an insoluble weak alkali resist film layer. The unnecessary part is covered by the film with the recorded pattern, and no photopolymerization reaction occurs.
5) Development: The active groups of the unexposed part react with the alkaline solution to form a soluble substance and dissolve, leaving the photosensitive cross-linked and cured part.
8. Graphic electroplating (electroplating copper)
After exposure and development, the circuits that need to thicken the copper layer are revealed, and the copper layer of the circuits is thickened by the electroplating copper process.
9. Etching and debasing
Remove the excess copper layer and dry film on the circuit, and etch away the copper layer and titanium layer attached to the surface of the substrate by the previous processes such as magnetron sputtering, chemical copper deposition, and pre-electroplating copper. The main processes include rough grinding, film stripping, copper etching, and titanium etching.
10. Annealing
Use an annealing furnace to bake the ceramic plate at high temperature to release the concentrated stress during electroplating, increase the ductility and toughness of the copper layer, and make the copper particles more densely stacked.
11. Sanding with abrasive belt
After annealing, a layer of oxide is attached to the surface of the substrate, and the surface is relatively rough. In order to prevent the quality of subsequent gold and silver products from not meeting the standards, it needs to be polished and removed. After polishing, the surface becomes smooth and flat.
12. Flying probe
A high-speed flying probe tester is used to test the short circuit of the through hole.
13. Sandblasting before solder mask
Before solder mask, the substrate circuit needs to be sandblasted to roughen and clean the surface, remove the oxide and dirt on the surface, etc. The specific process includes pickling, sandblasting, micro-etching and other main processing sections.
14. Solder mask printing
The purpose of solder mask printing is to apply a permanent interlayer material, called solder mask, on the conductors on the surface of the circuit board that do not need to be soldered. This allows the surface treatment or welding to be limited to a specified area during downstream assembly and welding, which protects the board surface from contamination during subsequent surface or welding and cleaning processes, and protects the circuit from oxidation and welding short circuits.
After solder mask ink is applied to the board surface by screen printing, it is sent to an ultraviolet exposure machine for exposure. The ink undergoes a polymerization reaction when exposed to ultraviolet light in the transparent area of the film, and the unexposed area of the coating is developed and removed with a sodium carbonate aqueous solution.
15. Sandblasting after welding
After the solder mask is printed, exposed and developed, the part to be welded is exposed. In order to achieve good results in the next process of gold/silver plating, the exposed part needs to be sandblasted to roughen the surface and remove the oxide attached to the copper surface.
16. Surface treatment
After the solder mask is completed, the pad position of the circuit board is plated with gold, silver and other metals by electroplating or chemical plating to ensure that the exposed terminal part has good solderability and anti-oxidation performance.
17. Laser cutting
The product is cut using laser cutting equipment.
18. Inspection
Use thickness gauge, AOI automatic optical inspection machine, ultrasonic scanning microscope and other inspection equipment to inspect the performance and appearance of the product.
19. Marking
Use the marking machine to print the product identification code on the ceramic substrate.
20. Packaging and shipment
Use the vacuum packaging machine to package the product and ship it.
The main production equipment of DPC process includes: laser drilling machine, drying equipment, laser coding machine, magnetron sputtering equipment, cleaning equipment, electroplating equipment, grinder, etching machine, annealing machine, sanding machine, plate grinding machine, high-speed flying probe test machine, sandblasting machine, screen printing machine, plate grinding machine, laminating machine, exposure machine, developer, annealing furnace, laser scribing machine, thickness gauge, AOI automatic optical inspection machine, ultrasonic scanning microscope, vacuum packaging machine, etc.