Every link in the process from the signing of the semiconductor precision mold manufacturing order to the delivery of the finished qualified mold to the customer may affect the quality of the mold. The precision mold manufacturing process is controlled by system engineering, and each link must be controlled. It is the core of semiconductor precision mold manufacturing. premise.
The guiding ideology of mold parts processing is to formulate corresponding process plans for different mold parts, different materials, different shapes and different technical requirements. The general process of mold parts is: blank preparation-rough machining-semi-finishing-heat treatment (quenching, conditioning)-precision grinding-electrical machining-fitter trimming and surface processing. Achieve the required processing accuracy by controlling each step of the processing process.
1,Semiconductor precision mold materials and heat treatment control.
The heat treatment of mold parts not only allows the parts to obtain the required material hardness, but also stabilizes the size and shape of the parts during processing and after processing. There are different heat treatment methods according to the different materials of the parts and the structural characteristics of the parts. The internal stress of the parts must be heat treated When controlling and formulating the heat treatment process, full consideration must be given to the material’s hardenability, hardenability, overheat sensitivity, and decarburization sensitivity. The pressure quenching process must be used for thin-walled parts.
(1) Precision mold material selection: In addition to CrWMn, Cr12, 40Cr, GCr15, Cr12MoV, 9Mn2V cemented carbide, for some concave molds and punches with high working intensity and harsh stress, you can choose high thermal stability Alloy steel ASP23, SKD-61, SKD-11, KH51, KH-9 tungsten steel, etc. with good properties and good microstructure.
(2) Stress relief treatment after quenching: Internal stress remains in the workpiece after quenching, which can easily lead to dimensional changes or even cracking of the workpiece after subsequent finishing. Therefore, parts should be tempered while hot after quenching to eliminate the impact of quenching stress on complex shapes and many internal and external corners. For workpieces, tempering is not enough to eliminate the quenching stress. Stress relief annealing or multiple aging treatments are required before finishing to fully release the stress.
2，Semiconductor precision mold grinding process control
Grinding is a key process in precision mold processing. Finishing grinding must strictly control the occurrence of grinding deformation and grinding cracks, and even control micro-cracks on the surface of the workpiece. The following aspects should be considered when formulating a precision grinding process.
(1) Select a grinding wheel: For mold materials with high tungsten, high vanadium, high molybdenum, high alloy, and high hardness, white steel jade grinding wheels and SDC green silicon carbide grinding wheels can be used; when processing cemented carbide, the quenching hardness is very high When the material is made, the diamond grinding wheel with organic binder is used. The organic binder grinding wheel has good self-sharpening properties. The precision of the ground workpiece is above 0.002mm, and the roughness can reach the requirement of Ra=0.16um. CBN cubic boron nitride grinding wheels are used for finishing on CNC forming grinders, coordinate grinders, and CNC internal and external cylindrical grinders, and the effect is better than other types of grinding wheels. During grinding processing, the grinding wheel must be trimmed in time to keep the grinding wheel sharp. When the grinding wheel is passivated, it will rub, score, and squeeze on the surface of the workpiece, causing burns, microscopic cracks, or grooves on the surface of the workpiece, affecting the processing accuracy.
(2) Selection of feed amount: The feed amount for precision grinding should be small, the cooling during grinding should be sufficient, and the coolant medium should be selected as much as possible. Parts with a machining allowance within 0.01mm should be ground at a constant temperature.
(3) Workpiece clamping: Shaft parts are characterized by multiple rotating surfaces. Precision machining methods are generally used during the grinding process of internal and external cylindrical grinders. The grinder chuck and tailstock apex are used to clamp and position the workpiece, or the head and tail are used to clamp and position the workpiece. The two centers position the workpiece. At this time, the line connecting the chuck and the center of the center is the center line of the workpiece after grinding. If the center line jumps, the coaxiality of the processed workpiece will not meet the requirements, so the chuck must be prepared before processing. When grinding the inner hole of the wall, consider using a clamping process table, which means leaving an extra thick wall part during turning, and then remove it after the grinding of the inner hole is completed.
3，EDM control
(1) Preparation for wire cutting processing: For wire cutting, a precision slow-moving wire cutting machine tool is used, with a processing accuracy of ±0.002mm and a roughness Ra=0.2um. Select a deionized waterline with high deionization degree and the verticality of the cutting wire meets the processing accuracy requirements. The wire material used for cutting with moderate tightness is adapted to the material of the workpiece to be cut, ensuring reasonable processing speed.
(2) Processing route design: Wire cutting processing destroys the original stress balance of the material during the processing, causing stress concentration at the corners. The method to deal with the stress concentration is to use the vector translation principle and leave 0.8~0.9mm before finishing. The remaining amount is pre-machined to roughly shape the cavity, and then heat treated to release the processing stress as much as possible before finishing to ensure thermal stability. When processing the punch, 4 passes of cutting are used. The cutting position and path of the cutting wire should be reasonably determined. The position of the blank should be selected after the first pass of cutting. The workpiece should not be in a cantilevered state. The workpiece should always be in a good stress state without any influence. Subsequent processing: drilling holes and threading wires on the blank, and the processing accuracy is guaranteed to be 0.002mm.
(3) EDM forming process: EDM forming requires the production of rough and fine electrodes respectively. Precision electrodes are processed with CNC machine tools. Cu-W alloy electrodes have good overall performance and less electrode loss than copper electrodes. Under good chip removal conditions, they can process difficult-to-machine materials and parts with complex cross-section shapes; Ag-W alloy electrodes It has better performance than Cu-W alloy electrode and is used for precision machining; graphite electrode uses imported graphite with low loss, high hardness, fast electric corrosion rate and low surface roughness. Arrange precise trimming before the end of EDM to remove the thin hardened layer formed on the surface.
4，Surface treatment and mold assembly
1) Surface treatment: After finishing, the surface of the workpiece will have no pores, uniform hardness, small differences in anisotropic properties, low inclusions, and no places where stress is concentrated such as tool marks and grinding marks left during machining. By polishing, grinding, and bench grinding, the unnecessary edges and sharp-angled holes of the workpiece are blunted. After electrical machining, the surface becomes off-white and 6~10m of modified hardened layer is removed. This layer is brittle and contains residual stress. The hardened layer must be fully eliminated before use.
(2) Mold assembly: Before assembly, the workpiece must be fully demagnetized and the surface cleaned with ethyl acetate. During the grinding and electrical machining process, the workpiece will be magnetized to a certain extent and has weak magnetic force, which can easily absorb some small debris for assembly. In the process: Fully understand the structure and technical requirements of the assembly drawing, and assemble various parts; correctly list the assembly sequence of each component; check the dimensional accuracy of each component, and clarify the coordination requirements; assemble all required Assembly tools; first assemble the guide posts, guide bushes and cavity forming block components of the mold base; assemble the template and combine the punch and concave molds to adjust the position of each plate; open and close the mold to check whether the mold action is accurate and reliable.
