1. Terminal mold design considerations
Mature products of terminal molds generally have two characteristics: large output and fast update period. Based on the characteristics of the product, when designing the terminal mold, the mold structure and ideas should be integrated from these two aspects. Let me share my personal feelings:
1. When designing and laying out the terminal mold, try to save as much material as possible. Under normal circumstances, the Pitch product or customer of the material strip has been determined and cannot be changed. Therefore, considering the material width, single material can be double row or double material can be double inserted. to improve material utilization.
2. When designing the mold, try to perform multiple processes in the same step, shorten the length of the mold as much as possible, and eliminate the cumulative errors caused by processing accuracy.
3. For those with strict bending angle/size requirements, there should be adjustment steps as much as possible. When adjusting, you only need to adjust on the punch without disassembling the mold.
In general, it is necessary to increase the stamping speed and dimensional stability, and reduce the cost of a single product. The profit of a single product of terminal products is relatively low, and it depends on high output to increase the overall profit.
2. Adjustment of strap deformation of terminal mold
When designing, assembling and repairing terminal molds, tie deformation is a very important aspect. There are three types of lace deformations: lace scimitar, lace twist, and lace snake. In fact, the lace snake shape is a combination of scimitar and twist. In English it is (Cabriole, Twist and Snake).
There are three ways to adjust the Cabriole. One is to prevent it from appearing and to press it where it appears. The second is to press in the opposite direction immediately after it appears. The third is to press and adjust the material strip when it is about to leave the mold, so that it can deform to offset the scimitar.
1. Is it because the layout is a single carrier? If so, you can add a stopper on the biased side, or you can try it first by increasing the pressure of the pressure plate.
2. Check and adjust the feeder.
3. Check whether the R angles of the male and female molds of the bent part are the same size and whether the forces on both sides are balanced (if it is a U-shaped bend).
4. In short, the main reason for this phenomenon is the problem of "force"
In terminal molds, especially in automotive terminal molds, multiple bends are also the main cause of lace deformation. Local strong pressure, adjustment mechanisms, reasonable bending steps and structures are all indispensable.
3. IC terminal mold
IC lead frame is a key metal component of semiconductor and information products. With the vigorous development of semiconductor and information industries, its market demand is huge and growing rapidly. IC lead frame stamping molds represent molds with the highest precision. They not only require advanced mold design technology, but also high-precision processing equipment (optical projection grinders and wire-cut electric discharge machines are indispensable tools).
1. Lead frame related process instructions
① IC process description
② Lead frame related technologies
A. Gold wire bonding (Wire bonding) Gold wires are extremely small, with a diameter of about 30 μm. The mold for drawing gold wires is currently manufactured by no one in China.
B. Lead frame material
IC lead frame materials mainly include iron-nickel alloy (also called 42 alloy because the nickel content accounts for 42%) and copper-based alloys (oxygen-free copper, deoxidized copper). The former accounts for about 20% of the usage, while the latter accounts for about 80%.
③ Lead frame production methods and trends
There are two ways to produce lead frames: stamping processing and etching processing. Among them, stamping processing is currently the mainstream. Due to the increasing demand for high-pin count lead frames, the application of etching processing is gradually receiving more attention.
2. Key points of lead frame stamping processing
① The front end of the inner lead of the lead frame requires high flatness, and the flat area is at least 0.1 mm (more than three times the diameter of the gold wire), so coining must be used.
② The lead space of each inner lead must be kept correct and even. The imprinting process will reduce this space, so the imprinting depth must be controlled and the lateral twist of the lead must be suppressed.
③ The position accuracy of the inner guide pin must be kept correct to facilitate the reliable adhesion of the wire bonding in the subsequent project. The corresponding strategy is to punch the inner guide pin first and then punch the outer guide pin. The stamping processing sequence must be properly designed, as well as the stamping process. A correction stage is designed to suppress the deviation of the lead frame lead position during stamping processing.
④ The flatness of the lead frame is required to ensure stability and smoothness during transportation and wire bonding in subsequent projects. The corresponding strategy is that when punching the lead pins, the amount of recurvature should be suppressed to a minimum and the direction of recurvature should be consistent. Also, the lead frame material should be subjected to a stress relief process before punching.
⑤ Deformations such as distortion or offset of the lead pins within the lead frame must be kept to a minimum to facilitate reliable operation of subsequent projects. The solution is to pay attention to the strong pressure design of the press plate in the mold, set the optimal mold gap and maintain the best condition of the cutting edge of the active components (punch and mother mold), and the mold guide device has high rigidity.
3. Key points in lead frame stamping die design
①Mold clearance
The lead frame stamping die gap is 3 to 5% of the plate thickness (3% for copper alloy, 4 to 5% for 42 alloy). The gap between the press plate and the punch will be smaller and should be less than 50% of the die gap.
② Pressing plate
The pressing force of the press plate is required to suppress the distortion caused by the stamping process and improve the quality of the punching surface of the guide pin. The pressing position should be concentrated near the punching load area (i.e., the punch guide part). The pressing force of the press plate The protruding design of the material is used to increase local pressure and subject the material to compressive stress to prevent distortion or recurve phenomena.
③Punching processing sequence
Proper punching processing sequence design is the most effective way to improve the punching deformation or distortion of the lead pins. It is difficult to correct the punching deformation or distortion of the lead pins through subsequent annealing operations. The following are the basic principles for considering the punching sequence:
A. Die cut the inner guide pin first, then punch the outer guide pin.
B. You can punch the short lead first and then the long lead, or you can punch the long lead first and then the short lead. Remember not to use a cross-cutting arrangement of the short lead and the long lead. form.
④Mother mold form
The shape of the master mold adopts straight section push-pull type or full push-pull design; depending on the processing method, the master mold shape adopts straight section push-pull type or full push-pull type design. The length of the straight section of the former is designed to be 3 mm, the push-out angle is 1/2°, and the processing method is grinding. The push-out angle of the latter is set, and the processing method is wire-cut electric discharge machining.
⑤Adjustment station design
In order to increase the strength of the mold or provide sufficient fixing space for the die, the empty station is an important part of the continuous die design. In addition, in order to suppress the distortion or deformation of the lead frame during the punching process, the design of the adjustment station is a key point that must be considered.
4. Mold rigidity and guidance method
① The mold guidance method adopts dual guidance, that is, the main guide post (Main guide post) and the auxiliary guide post (Sub guide post) are used together.
② The number of outer guide pillars is an even number design. When the mold size is less than 600 mm, it is designed with six outer guide pillars. When the mold size is larger than 800 mm, it is designed with eight outer guide pillars.
③ Use high-rigidity roller guides to improve guidance accuracy and rigidity.
④ The inner guide device adopts the fully guided type (also known as the three-platen fully guided method), that is, the inner guide column passes through the punch plate, press plate and mother plate.
5. IC lead frame stamping die processing technology trends
Lead frame stamping die demand trend
a. Molds are becoming smaller
Due to the development of wire electric discharge machining (WEDM) technology, the machining accuracy and surface quality have been improved. Therefore, it is gradually possible to use WEDM method to process the mother module or press plate into the block instead of grinding process, which can reduce the number of stamping engineering stations. The number of molds (the design of empty stations can be reduced) greatly reduces the size of the mold. In order to match the specifications of high-speed punching machines, the size of the punching mold for lead frames with multiple pins (more than 100 pins) reaches a length of more than 1200 mm, so the stamping production method must adopt a punch press serial arrangement type.
b. Mold components are becoming smaller and more precise
Taking lead punches for lead frames with multiple pin counts as an example, the trends in shape and size are toward smaller outer dimensions, shorter blade lengths, and thinner punches, while their accuracy trends are toward high precision and low processing costs. Surface roughness progress. In order to achieve such high precision (dimensional tolerance ±2 μm or less) and low surface roughness (0.3 μm Ra or less) requirements, it is necessary to use high-precision grinding equipment and low surface roughness wire-cut electric discharge machines.
6. Key technologies for lead frame stamping die processing
①High precision/surface roughness grinding
A. Optical projection grinding.
B. High-speed reciprocating grinding.
C. Grinding of tool molds and fixtures.
D. Mirror polishing (Lapping).
②Wire electrical discharge machining (WEDM)
A. Oil wire electric discharge machining.
B. Water-type wire cutting electric discharge machining.
C. Low-deterioration layer wire-cut electrical discharge machining.
③Mold materials and processing technology
A. Mold heat treatment technology.
B. PVD, CVD, TD, etc.
C. Super hard mold material diamond coating.
D. Ultra-fine particle super-hard mold material.
