PCB track below the components

Hi,

I want to make single layer pcb. All components are smd.
can i make path crossing to resistor(between it's pads)?

do frequency will disturb path or resistor(its property)?

same question with inductor and capacitor.
i think it will disturb in inductor and capacitor case.

i will take 5v input for my circuit from usb.
so, SMD male usb connector or SMD micro usb female will better?
i don't want any holes in pcb. which one will handle force occurred during connection?
is there any chances for abrupt pads due to no holes= no support?

thanks,
vraj

Re: pcb track below the components

Hi,

I'm no friend of single sided PCBs. Maybe for homebrew, but then yuo will have problems with precision etching the thin structures needed when you put traces underneath SMD parts.

But usually you may use tracks underneathSMD parts.
You have to consider:
* capacitive coupling of signals
* voltage rating, isolation issues, leakage currents
* manufacturing restrictions like minimal trace width, minimum distance between copper
* mind the increased opening of the solder stop, and it's placement tolerance, to avoid short circuits caused by solder
* mechanical stress, increased cracking rate

Klaus

Re: pcb track below the components

Single-sided PCBs have inherent GND issues, which can be particularly critical in your case where there is a high speed signal.

i don't want any holes in pcb. which one will handle force occurred during connection?
is there any chances for abrupt pads due to no holes= no support?

Click to expand...

PTH components has 2 solder points to tie them on board at each side, therefore, a priori the assembly should be mechanically more robust.

Re: pcb track below the components

hi,

yes, you are correct.
single sided pcb has low rate than multi layer pcb.
so i decided to do so.

now i am thinking to add jumpers(0ohm resistor) to complete pcb:wink:

will it cause problem?
do you use auto route ? is it good?
i am working on EASY EDA software. it couldn't able to auto route even in two layers!

thanks
vraj

Re: pcb track below the components

now i am thinking to add jumpers(0ohm resistor) to complete pcb

Click to expand...

Still not clear if you will really do on single or double face. If on double face 0R0 jumpers do not make sense at all, once vias can connect ground everywhere, but if you want to use PTH jumpers, it is advisable to use the same footprint for all of them, once this way you can format at the cutting machine just once, instead of changing according to different jumper sizes.

- - - Updated - - -

do you use auto route ? is it good?

Click to expand...

Nothing compares to the good judgment of a human being who knows what he is doing, and it is not uncommon to find really questionable routing made by automatic routers of these tool. I would just rely on a 'professional' autorouter in which a lot of time was spent configuring it

Re: pcb track below the components

hi,

i am making smd pcb. there may be no holes.
i calculated and compare cost for single side(with jumpers) and multi layer pcb. as result, multiplayer pcb was cheapest.
so i will try with 2 layers.
easy EDA software was unable to do auto route also with 2 layers. so, i have to connect components by myself. i am using qfn 4*4, 0402, sot23 packages.

i use easy EDA because its easy.

but i still need help, is there any suggestion to start with 2 layer pcb?
do i make most of bottom portion with ground?

thanks,
vraj

Re: pcb track below the components

Hi,

if you want to buy the PCB, then: Yes. Bottom = GND.
Use a via from each IC pin to the bottom side.

About everything is possible with 2 layers....Its a question of your effort.
For sure it depends on IC connections, board area restrictions, signal freqency and so on..

Klaus

Re: pcb track below the components

It al depends of the circuit needs. If it has precision analog parts, then a single sided will allow too much ambient noise to perturbate the signals. If it's a high speed circuit, then crossing paths is not a good idea due to EMF generated by tracks (that theorically doesn't affect if they are perpendicular, but that will make the routing labour much longer and delicate, whithout saying it might take more space, increasing manufacturing costs which I see it does matter in your case).

There is absolutely no problem in pure digital signals and supply tracks to be crossed in any part, but keep in mind the implementation of 100nF decoupling capacitors near the ICs. The same doesn't happen with an ADC, which is digital but needs (or it should have) a very well filtered and noiseless supply to get accurate measurements.

Auto routing? I personally don't like them, but you always have the choice. If you can afford a 2000USD licence to a good auto router, then you will have to spend about an hour or more to configure it (tracks widths for each class, clearances, positions, rotations allowed, rooms, connectors zones, etc) and then wait till it gets it done. Sometimes you will not get the spected results.
I prefer to trust the human capability to place each thing in its place, ordering the sub circuits and keeping space for silkscreen notes. Oh, and making it easy to repair if it would suffer any failure.

As you mention a USB, I assume (it could not be too) it's purely digital, so a single sided PCB should work fine. The SMD micro USB is smaller and has more soldering area. The male (class A) connector needs holes in the PCB (thing you don't seem to want) but it seems stronger, since the through hole terminals give an extra mechanical resistance, and a disadvantage of it is that if connected directly to the PC, it could suffer a strain that could damage both PCB and PC port.