Electronics > Manufacturing & Assembly

Video showing 4L PCB manufacturing process

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--- Quote from: Mechatrommer on March 06, 2014, 10:36:23 pm ---i dont see how internal buried vias are made and plated. they went straight to layer press before drilling indicating either the board they used for demo doesnt have internal buried vias or they dont support it? i need some light on this thank you.

--- End quote ---

The needs of the circuit board dictate the layer stackup that is used. At an (albiet slightly) educated guess, The general stackup for a 4-layer board would be a thin, dual sided laminate, a thin Pre-preg board with no copper on it, and then another thin, dual sided laminate.

To get blind vias (which start external and end part way through, can be done before the boards are all sandwiched together, by drilling the relevant holes and copper plating the board, like regular vias. The board is then sandwiched together after etching, and the final drill/plating/etching is completed.

To get buried vias, you need to alter the stackup so that you can drill the vias for the internal layer first. So for a 4 layer board, your stackup might turn out to be pre-preg, then dual layer PCB, then pre-preg. You would drill/plate etch the internal PCB like usual, then add the pre-preg to the outside. However Pre-preg doesnt come with another copper layer, so you then have to manually add in another layer of copper top and bottom, when you press and set the pre-preg material.

Doing it this way also limits your options on doing blind vias. The two ways I see it being possible are either only adding one pre-preg at a time, and re-drilling/plating for the blind vias, or if you have accurate enough machines (read $$$Pricey$$$) You can drill just down far enough to hit an internal drilled/plated hole.

Basically the reason that manufacturers don't do blind/buried vias is because the process can take a lot longer, and can cost a lot more money then the hassle it is worth. The exception to the rule there of course is quantity. If you are looking at signing contracts for significant quantities of boards, the board houses are going to be happy to do it for you for a price. :)

Hopefully that helps

yes thats my guess that buried vias will add extra steps in the process (hence cost), but it will be wonderfull to see some process of it, but o well i can have some imagination right now. and i guess buried vias for 4 layers board will be pretty seldom since everybody is like doing internal planes for power and ground. thanks.

internal buried vias need extra processing steps not shown in that video (essentially a two-layer pcb is made first then sandwiched between the outer layers. That limits the possible stack-ups too). That's why they're so much more expensive (if the factory makes them at all), not common for 4-layer prototype boards.

this video is very old, but the manufacturing process is advanced. It's a professional pcb manufacturer.

video is not better than you come and visit factory to witness the PCB manufacturing process. *REMOVED*  you could go into the page to know more about PCB parameter, materials,specification, etc.


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