Some doubts about PCB USB connectors

Question

I'm trying to make a PCB where I have USB connectors, but I'm really new into this and I'm trying to solve a few questions online about the theme, if you could guide me online through the theme that would be great. For this purpose, this systems is a USB sensor with 2 USB connectors (one male for PC connection and a female for bus extension) and, besides the sensor and MCU, will have switches to let us cut the VCC line of USB.

The main issues in my mind are:

1. What's the difference between the several USB connectors materials? I found some that say they have shield, others are gold plated and there are so many that I just quit looking online for everything
2. For mechanical resistance, is there any special type of connector? (this board will have switches and one of the connectors could be connected to the PC USB).
3. Is it cheaper (this is for a school project, but we might try to sell it after) to make a USB Male connector using only PCB (like this) or buy and solder a connector?

Basically I'm trying to find some kind of "USB connectors in PCB for dummies" guide, but Google isn't helping me that much.

EDIT

The "bus extension" will be for VCC and GND and that's just for sharing the power switches that I talked above, there is no hubs involved in this.

Answer 1

Note "bus extension" in this situation will only work if the device it's going to is purely passive (doesn't use the data lines) or you have a hub on the board.

0) Yes, it always takes absolutely ages to find the right parts and import them into your PCB tool. And there are always way too many of the wrong sort of parts.

1) "Shielded" connectors are the normal sort with a rectangular metal casing. Pick one of those. Not having a shield might give you interference problems (probably won't, but it's such a pain to diagnose). It also makes the mechanical connection more solid.

Gold plating is an affordable luxury that stops the contacts corroding. Less of an issue for contacts that are hidden away from fingers, but still nice to have if you care about longevity.

2) Through-hole is generally stronger than surface-mount. Some have extra plastic or metal mounting lugs to really lock it to the PCB.

3) The PCB-only connector requires that you get a PCB made of the required thickness. It sits a little more loosely in sockets, but it works and is very cheap. It also looks cheap. Connectorless USB on a PCB

Answer 2

To expand the good answer from pjc50.

Re the physical elements, there is standard plating defined for all USB connectors specified by the USB-IF (Implementers Forum), however over time those standards eroded as customers work out they can use less gold, and hence lower cost connectors in some circumstances.

Full size USB2.0 connectors (A & B types)have been in the market for many years and the defacto industry standard is now gold flash (thin gold) plating.

While for more recent variations of USB connectors such as Micro USB or USB3.0 the plating standard remains 30µ" gold thickness on the mating contacts.

The thicker gold achieves environmental protection(resistance to corrosion) but equally importantly supports the number of mating cyles.

Normal mating cycles for full size USB2.0 A & B is 1,500 with gold flash plating.

Micro USB2.0 types achieve 10,000 cycles with 30µ" plating, this is not only achieved by thicker plating, but by the contact design putting more pressure on the cable plug.

I'm sure for your project this number of cycles is not a concern, so pretty much whatever you pick up from the shelf on Farnell would be fine.

Shielding - All USB connectors are shielded to a point, if you're passing through a panel you should consider whether you require to choose panel fingers or not, here's an example of a drawing with a grounding shell option http://gct.co/usb-connectors/pdf/USB1035.pdf The fingers would ground the connector to the panel.