In the design of rigid-flex PCB, how much spacing should be designed between vias and the PCB area?

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In the design of rigid-flex PCB, how much spacing should be designed between vias and the PCB area? [Copy link]

Yibo Expressway Member: Wang Huidong

The fragrance of cherry blossoms is endless.

The branches are full of beautiful flowers.

The spring breeze knows not the youth's heart,

The rosy pink looks like smoke under the tree.

On Saturday afternoon, Zhao Ligong opened the window and a fragrant breeze blew in, and the air was filled with the scent of cherry blossoms. The cherry blossoms were blooming romantically, just like the heart of a young man.

Zhao Ligong looked back at Ruyan, the girl who looked like a fairy fallen into the mortal world, and said softly:

"The Ruyan cherry blossoms are in bloom. I'll throw the board down in a bit. Let's go see the cherry blossoms together."

Ruyan smiled and said, "I'll listen to you."

After a while, Engineer Zhao finished his work, winked at Ruyan behind him, and the two of them walked out of the office happily.

Today the flowers are like snow-capped mountains and the cherry blossoms are like beauties.

The boy and the beauty were having a great time when the eldest senior brother called.

Zhao Ligong's heart skipped a beat, and he had a premonition that something bad was going to happen.

On the cherry tree, the bees are busy collecting nectar, but my heart is as confused as a fly.

Ligong Zhao designed an 8-layer rigid-flex board with two layers of FPC, reasonable stacking, orderly routing, and a good density.

Can't figure out what the problem is.

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The senior brother said that the holes punched in the hard board area are too close to the soft board area, less than 1mm, which will cause reliability problems in production.

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Zhao Ligong looked up at the cherry blossoms on the tree, then looked at Ruyan under the tree, and said, "This..."

The eldest brother said: "Don't worry, I will briefly tell you the reason."

The processing flow of the rigid-flex board is as follows: first, after completing each process, combine them before pressing, then press production, and finally open the cover to expose the flexible board area to form the rigid-flex board effect.

The picture below shows the processing flow of rigid-flex PCB, which is more confusing than looking at cherry blossoms.

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When producing rigid-flex PCB, a special material is used - non-flow PP, which is what we often call no-flow PP.

Before the production of the rigid-flex board, the non-glue PP in the soft board area must be milled off to form a cavity. This prevents the FPC area that needs to be exposed from being bonded together during lamination. As shown in the following figure:

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In actual production, PP glue is not involved in such places.

Although it is called non-flowing PP, it does not mean that its glue does not flow. It just has poor fluidity during pressing.

The following figure shows the PP picture with the FPC area milled out

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IPC-A-6013 stipulates the acceptance standard for the overflow area of rigid-flex boards - the overflow range is within 1.5mm. In fact, this standard is very broad in the industry.

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However, in actual production, customers usually have stricter requirements for the scope of the overflow area in order to prevent quality abnormalities. In order to prevent the glue of the non-glue PP from overflowing the board and appearing in the FPC area. Usually during processing, the non-glue PP is shrunk by 0.5-1mm to avoid the risk of overflow. Then when the board is pressed together, there is a 0.5-1mm area in the area of the hard board close to the FPC where there may be no glue. When we drill holes after pressing, if the holes are too close to such areas, the area penetrated by the drill may be a hollow area. Then the chemical solutions of the subsequent electroplating, etching and other processes may enter the FPC cavity area, resulting in abnormal circuits in the FPC area.

The picture below shows that the hole is too close to the FPC area, causing the electroplating solution to enter the cavity area of the FPC, resulting in production abnormalities and scrap.

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The final sentence summarizes:

The distance from the via hole to the edge of the rigid-flex junction is designed to be at least 1mm. Since the cover film of the high-reliability rigid-flex board is partially bonded and also extends into the hard board area by 1mm, the via hole must be avoided to prevent production abnormalities.

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Ending:

Senior Brother said that in order not to disturb your spring outing and viewing of flowers, I helped you modify the design.

Zhao Ligong breathed a sigh of relief, raised his head and glanced at Ruyan who had sneaked up to him at some point.

The spring breeze is warm, the flowers are in full bloom, and the beauty is still there.

qwqwqw2088

Here are two 1mm

How to explain, what does at least 1mm mean?

In the design of rigid-flex PCB, how much spacing should be designed between vias and the PCB area? [Copy link]

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