# Efficient assembly/fabrication of PCBs differing only in solder jumper configurations

I have a PCB design with solder jumpers which need to be bridged to select specific functionality - say A and B. Half of the PCBs are going to have A and the other half B bridged.

Is there an efficient way (read: cost-effective) to manufacture such PCBs (i.e. so that it is still "counted" as one design as opposed to two)?

Use a zero-ohm SMT resistor for the strap. The cost of the resistor is about as close to nothing as you can get (tenths of a penny, even on Digi-Key) and will be reliable. You call out which version by using a different bill of material (BOM) when you go to build the board.

Using a solder bridge would not be reliable, and will not pass DFM analysis at the manufacturing side. (They actually design their processes to avoid bridging.)

Even worse, you'd have to have different pastemasks which will far outweigh the cost of the resistors. A pastemask costs about $500 for a small board. For that, you can buy about 500,000 resistors. The very cheapest way of all if you are fortunate enough to have extreme high volumes is to have a different PCB for each variant. You generally don't want to order more boards than you can consume within 3 months or so, as the boards will oxidize if they sit too long and thus have yield problems. As far as layout concerns, for fullspeed USB you don't have significant SI issues that would be caused by such a jumper. Even USB highspeed would be just fine with the strap in series, though you'd need to pay more attention to stubs. • When you say "pastemask" do you mean the stencil? In my experience you can get top+bot stencil for less than 100$ even for 10pcs prototypes. – Bonnevie Aug 21 '19 at 5:36
• That’s still 100,000 resistors. – hacktastical Aug 21 '19 at 6:25

One sure way to avoid any fees is to do this with something that is settable yourself, like an 0.1" jumper header. Another way is with a dip switch.

It really depends on the manufacturer. Some might want to charge you more, some might not care. Ask them how much they charge for variants.

I do this with 0603 resistors, because they are listed as different product numbers they end up being ordered separately by our manufacturing division we don't save any money because we use the same PCB.

• I've been pondering on the use of 0 Ohm resistors, but I figured it might theoretically be cheaper to create bridges with solder paste exclusively (since that's one less part that needs to be placed). In my case I'll be routing between USB (FullSpeed) and I2C signals, so I'd like to avoid mechanical connections. – mewa Aug 20 '19 at 22:46
• You should be able to use USB fullspeed with a 0 ohm jumper. The 0 ohm jumper does add a slight bit of inductance, be careful with the routing. For USB fullspeed\regular speed experiments I have used a combination of 0 ohm jumpers and not loading the phy to switch between options. I2C won't be affected by 0 ohm jumpers for sure. – Voltage Spike Aug 20 '19 at 22:50