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Third, the line production mainly considers the impact of line etching
Due to the influence of side corrosion, copper thickness and different processing techniques are considered during production and processing, and a certain pre-roughness of the line is required. The conventional compensation of HOZ copper for tin spraying and immersion gold is 0.025mm, and the conventional compensation for 1OZ copper thickness is 0.05-0.075mm, and the line width is /Line spacing production and processing capacity is conventionally 0.075/0.075mm. Therefore, when designing the most line width/line spacing wiring, it is necessary to consider the compensation during production.
The gold-plated board does not need to remove the gold-plated layer on the circuit after etching, and the line width is not reduced, so there is no need for compensation. However, it should be noted that because side etching still exists, the width of the copper skin under the gold layer will be smaller than the width of the gold layer. If the copper thickness is too thick or the etching is too much, the gold surface will easily collapse, resulting in poor soldering.
For circuits with characteristic impedance requirements, the line width/line spacing requirements will be more stringent.
Fourth, the more troublesome part of the solder mask production is the solder mask treatment method on the vias:
In addition to the conductive function of the via, many PCB board design engineers will design it as an online test point for the finished product after assembling the components, and even a very small number of them are also designed as component plug-in holes. In the conventional via design, in order to prevent the soldering from being tinted, it will be designed as a cover oil. If it is a test point or a plug-in hole, the window must be opened.
However, the through hole cover oil of the tin-sprayed circuit board is very easy to cause the tin beads to be embedded in the hole, so a considerable part of the products are designed as the through hole plug oil, and the position of the BGA is also treated as the plug oil for the convenience of packaging the BGA. But when the hole diameter is larger than 0.6mm, it will increase the difficulty of plugging oil (the plug is not full). Therefore, the spray tin plate is also designed as a half-open window with a larger than the hole diameter of 0.065mm on one side, and the hole wall and hole edge are within the range of 0.065mm. Spray tin.
Five, the character processing mainly considers the addition of pads and related marks on the characters.
Because the component layout is getting denser, and it is necessary to consider that the pad cannot be placed when the characters are printed, at least ensure that the distance between the characters and the pad is more than 0.15mm, sometimes the component frame and component symbols cannot be completely distributed on the circuit board. Fortunately, it is now pasted. Most of the film is complete by the machine, so if it is really impossible to adjust the design, you can consider printing only the character frame instead of the component symbol.
Commonly added contents of the mark include supplier identification, UL demonstration mark, flame-retardant rating, anti-static mark, production cycle, customer-specified identification, and so on. The meaning of each sign must be clarified, and it is best to leave it aside and specify where to place it.
Sixth, the influence of the surface coating (plating) layer of the PCB board on the design:
At present, the most widely used conventional surface treatment methods include OSP gold plating, immersion gold, and tin spraying.
We can compare the advantages and disadvantages of each in terms of cost, weldability, wear resistance, oxidation resistance, different production processes, drilling and circuit modification.
OSP process: low cost, good conductivity and flatness, but poor oxidation resistance, which is not conducive to storage. The drilling compensation is conventionally made by 0.1mm, and the HOZ copper thickness compensation is 0.025mm. Considering that it is very easy to be oxidized and contaminated with dust, the OSP process is completed after the forming and cleaning. When the size of the single chip is less than 80MM, the splicing form must be considered delivery.
Nickel-gold electroplating process: good oxidation resistance and wear resistance. When used in plugs or contact points, the thickness of the gold layer is greater than or equal to 1.3um. The thickness of the gold layer used for welding is usually 0.05-0.1um, but the relative solderability Poor. The drilling compensation is made according to 0.1mm, and the line width is not compensated. Note that when the copper thickness is more than 1OZ, the copper layer under the surface gold layer is likely to cause excessive etching and collapse, causing solderability problems. Gold plating requires current assistance. The gold plating process is designed before etching. The complete surface treatment also plays a role of corrosion resistance. After etching, the process of removing corrosion resistance is reduced, which is why the line width is not compensated.
Electroless nickel gold plating (immersion gold) process: good oxidation resistance, good toughness, smooth plating is widely used in SMT boards, drilling compensation is made at 0.15mm, and HOZ copper thickness compensation is 0.025mm, because the immersion gold process is designed After solder mask, you need to use corrosion resistance protection before etching. After etching, you need to remove the corrosion resistance. Therefore, the line width compensation is more than that of the gold-plated board. For large-area copper-clad boards, the amount of gold salt consumed by immersion gold boards is significantly lower than that of gold-plated boards.
Spray tin plate (63 tin/37 lead) process: relatively best oxidation resistance, toughness, poor flatness, drilling compensation is made at 0.15mm, HOZ copper thickness line width compensation is 0.025mm, the process is basically the same as that of sinking gold Consistent, it is currently the most common surface treatment method.
As the EU put forward the ROHS directive, it refused to use six hazardous substances containing lead, mercury, cadmium, hexavalent chromium, polybrominated diphenyl ethers (PBDE) and polybrominated biphenyls (PBB). The surface treatment introduced pure tin (tin copper
7. Jigsaw puzzle and shape making are also difficult to consider comprehensively when designing:
First of all, the ease of processing should be considered when the board is assembled. The time distance of the electric milling shape should be assembled according to a milling cutter diameter (conventional 1.6 1.2 1.0 0.8). When punching the board shape, pay attention to whether the distance from the hole and line to the edge of the board is greater than a board thickness. The minimum punching size must be greater than 0.8mm. If the V-CUT connection is used, the edge of the board and the copper must be 0.3mm away from the center of the V-CUT.
Secondly, we must consider the problem of the utilization rate of large materials. Because the specifications of large materials are relatively fixed, the commonly used sheet materials are 930X1245, 1040X1245, 1090X1245 and other specifications. If the delivery unit is unreasonably assembled, it is easy to cause waste of sheet materials.
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