PCB manufacturability design and case study

Via is a point that is difficult to cirumvent in the PCB design process. In the process of Layout wiring, it is often difficult to realize that the lines do not cross at all. Therefore, on the basis of a single panel, through the via ( via) to achieve inter-layer conduction, and gradually developed double-sided and multi-layer boards, and vias have become a key point in PCB design.

From a design point of view, vias are usually used to achieve two functions: electrical connection, support or positioning, one is to meet electrical characteristics, and the other is to achieve physical requirements.

 

Therefore, sometimes the vias are classified into: vias, support holes, and support holes are divided into device welding holes (this type of holes are basically metallized holes) and device mounting holes (this type of holes) Most of the holes are not metallized).

 

From the design point of view, a via is mainly composed of two parts, one is the drill hole in the middle, and the other is the pad area around the drill hole. The size of these two parts determines the size of the via. .

Obviously, when designing high-speed and high-density PCBs, designers always want the vias to be as small as possible, so that more wiring space can be left on the board. In addition, the smaller the vias, the greater the parasitic capacitance. Small, more suitable for high-speed circuits .

However, the reduction in hole size also brings an increase in cost, and the size of the via hole cannot be reduced indefinitely. It is limited by process technologies such as drilling (drill) and electroplating (pla TI ng): the smaller the hole , the longer it takes to drill, the easier it is to deviate from the center position; and when the depth of the hole exceeds 6 times the diameter of the drilled hole, it cannot be guaranteed that the hole wall can be uniformly plated with copper.

Therefore, there are still many issues that need to be considered in comprehensive design and production. Some designers scrutinize the layout, and their PCB layout files can be sent directly to the production floor for production; others require more inspection by engineering before they can be sent to the production floor.

Often, these issues lead to delays and yield or reliability issues. The budgeting and production planning issues that arise due to this type of design are actually avoidable.

As a high-reliability multilayer board manufacturer,PCB HERO focuses on PCB R&D and manufacturing, providing customers with high-reliability and short-term delivery experience. "Reducing costs and increasing efficiency for the electronics industry" is our mission. We are well aware that in the main production chain, although the cost of product design, development and design engineering does not account for a high proportion, it will have a great impact on the total cost.

In view of the important role of the product design stage on the quality and cost of the final product, the following will combine some practical cases to share expert solutions for some problems in the design, so as to help reduce costs and increase efficiency in the whole process.

Hole Design Case 1: Hole (PTH/NPTH) design and line connection should not be unconventional

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question:

①As shown on the left picture above, the corresponding lines such as the hole plate have electrical performance connections, but non-metal holes are required; as shown on the right picture above, the corresponding lines such as the hole plate have no electrical performance connections, but metal holes are required.

Expert advice:

① According to the standard design, if a non-metal hole is to be made, first ensure that the corresponding line has no electrical performance connection, and the disk is the same size as the hole design or has no disk; if a metal hole is to be made, ensure that there is an electrical performance connection, or the disk is larger than the hole. The edge is about 5mil;

In addition, note that if metal holes are to be made but there is no disk in the corresponding circuit position, the back end must go through the positive electroplating process, and the delivery time will be extended by more than one day compared to the negative process, so this design is not recommended.

Correct design:

b5fc8e88-1b5e-11ed-ba43-dac502259ad0.jpg

Non-metallic hole in the left picture Metal hole in the right picture

②The additional hole table is attached to mark clearly which are metal holes and which are non-metal holes; pay attention to also try to avoid big misleading such as hole plate, no electrical performance connection but metal hole design is misleading, which leads to unnecessary time-consuming EQ communication.

Correct design:

b6088be8-1b5e-11ed-ba43-dac502259ad0.jpg

Hole Design Case 2: Slot (Metal/Non-Metal) Layer Design Distinction and Normalization

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question:

① There are 7 slots in the upper right corner of the figure. The customer requires the middle three to be made of non-metal slots, and the four slots in the red position (corresponding to the circuit layer with disks) are required to be made of metal slots, but these slots are uniformly designed on the gdd layer, which is normally the default. All are to be made of non-metallic grooves, and the rear end will open the disk to prevent copper exposure during groove milling.

Expert advice:

① Separate design, the non-metal slot is placed on the gdd or gm1 layer, the metal slot is placed on the drl layer, or the Slot layer is output separately

Correct design:

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Hole Design Case 3: Standardize the hole symbol, don't "hide" the slot

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question:

①The hole symbol mark in the design file is too large. When the back end checks whether the hole and the hole symbol correspond one by one, there is no way to start, and the hole position and size deviation caused by the import scale problem cannot be found;

②The slot is designed in the corner of the hole symbol, and the hole table is not marked, which is easy to be missed.

Expert advice:

① When designing the hole symbol, do not design it so big, and it can be clearly seen one by one corresponding to the drilling;

②Provide a hole table, mark the position and parameters of the slot, or put it into the through-hole drl layer;

Correct design:

b64bc32c-1b5e-11ed-ba43-dac502259ad0.jpg

Hole Design Case 4: Standardize the hole symbol, don't "hide" the slot

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question:

①The design of the hole symbol is very good, but the actual position of the hole design has to be a slot, the design is unreasonable and the slot has no additional description

Expert advice:

①Do not design holes and grooves in the same position; provide a hole table, mark the position and parameters of the grooves, and design the corresponding grooves directly on the drl layer;

Correct design:

b669dcf4-1b5e-11ed-ba43-dac502259ad0.jpg

Hole Design Case 5: Don't "lock up" the slot when designing the PCB file

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question:

When converting PCB files to geber files, slot locking is easy to miss

Expert advice:

① For files designed in versions before AD16, when providing PCB files, pay extra attention to unlocking the slot design, so that the slot design will not be leaked when transferring files;

Correct design:

b69d7028-1b5e-11ed-ba43-dac502259ad0.jpg

Hole design case 6: Solder mask ink plug hole via hole tolerance should not exceed 0.2mm

question:

①The solder mask plug hole is extremely poor, the large hole plug hole is not full, or the small hole ink plug hole is too much.

Expert advice:

①When designing via plug holes, the plug hole range should not exceed 0.2mm

Correct design:

Via(max)-Via(min) requirements≤0.2mm

The above are 6 PCB via design optimization cases. In general, using some best practices and using common sense steps in the design stage can save a lot of time, focusing on preventive design, supplemented by design modification, and making the pass rate Higher and more efficient.