Through-hole component connected from the top and soldered from the bottom?

I’m going to use a crystal Through-hole component, and this one can soldered only in the bottom because the top is not accessible,

normally in home-made PCB the track have to come from the bottom side. But when I took a look at the GERBER file of the STM32-DISCVEORY BOARD I noticed that the crystal is soldered from the BOTTOM and the track comes to him from the TOP. And the same thing for the connector…

That mean the professional PCB connect automatically the TOP and BOTTOM through holes together???

Pretty much all the fab houses will plate the through holes, Kicad considers the top and the bottom copper connected by default when you open new design project. You’ll need to specify unplated holes as exceptions if you want to avoid plating.

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That is exactly correct. The process that connects the top pads to the bottom pads (and any internal pads, too) is called “plating”. Here’s a random diagram I found online showing a cross-section of a plated PCB hole:

Notice the metal layer inside the hole that connects the top and bottom pads together. The plating also makes the pads less prone to lifting off the board when soldering.

Plating the holes like that is standard practice for any professional PCB manufacturer making 2 or more layer boards, though as Dolganoff stated, it is also usually possible to get unplated holes where needed. If you order boards from a hobbyist-oriented company like OSHpark or ExpressPCB, you can get boards with plated holes, solder masks, and silkscreen layers pretty inexpensively. The low-cost manufacturers generally place extra restrictions on board designs to eliminate process steps and keep costs down; for example, unplated holes are not available from OSHpark, since mixing plated and unplated holes on a panel requires at least two separate drilling processes.

Full-service PCB manufacturers can make anything physically possible for you, but their pricing is usually much too high for hobbyists. The low-cost manufacturers usually reduce costs by including many different PCB orders on each PCB panel, so that the setup costs are spread across many orders. When you use a full-service PCB manufacturer, you pay for entire panels even if you just need one little board.


thx everybody.

i have two question about the plating process :

  • if i design a through-hole component with diameter for example 1mm i’ll get a final hole less than 1mm (let’s say 0.9mm) because of the plating process take a little bit of space ???

  • for example if the Ethernet connector doesn’t fit to the board because the holes was too tight. so i have to use my own drill to enlarge the holes. in this case i’ll loose the plating between the two holes ???

Good question. Look at this thread: