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Quick PCB design questions

TheMaster

Jul 20, 2016
47
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Jul 20, 2016
Messages
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I'm designing my first PCB for a mass production product. They layout is complete, and I would like to put a few questions to rest before I order prototypes. I truly appreciate any advice given, and I hope that my questions are clear:

The board is rectangular, one layer, one sided, SMD, and destined for automated assembly.
  1. Are SMD pads in effect the same as copper traces? I don't mean functionally, I mean are they both just metallic etchings; are they composed in the same manner? I ask, because I incorporate this battery holder into my design. For the negative (circular) terminal, I placed a pad in my board design, although nothing is to be soldered to that pad, only the battery will sit on it. Is this correct to do?
  2. What is the difference between solder mask and paste mask? What does it mean to apply a mask to a pad? In NI Ultiboard, the "properties" tab of each pad there are two check boxes, "Solder Mask" and "Paste Mask" What is the difference, and what does it do to a pad when you apply a mask? I though masks are only for traces, and that pads must be exposed...
  3. In my design, I need to have 2 in-going wires which are to be soldered to the board, and 2 out-going wires which leave the board. I want them to be soldered permanently without using a jumper. From what I understand, this is typically done by soldering them to a hole. I don't think these instructions are something which are included in the design file, so how can I instruct a manufacturer to perform this procedure, do I simply provide an annotation or pass the information by some other means?
  4. It is important for the bottom of my board to be flush, because it has to fit into a flat housing. All components are top side SMD, but as I mentioned before I need to drill holes for the in-going/out-going wires. It is vital that these wires do not protrude all the way through the board, so that the bottom side remains flat. How can I accomplish this? If I drill blind holes, would that increase the cost? By what other means can this be accomplished?
Thanks for any help!
 

garublador

Oct 14, 2014
111
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Oct 14, 2014
Messages
111
The way the outer layers of a PCB work is there is the layer of copper, which consists of your pads, traces and fills. Then there's a layer of soler mask, which is the (typically) green stuff that covers most of the copper and prevents solder from wicking from the pads to the traces and gives some degree of protection. Then they give the exposed pads some sort of protective coating to prevent oxidation (usually gold, silver or solder). With that in mind:

1) SMT pads are just areas of copper that do not have solder mask over them but do have the protective coating. If I'm understanding that part correctly (the battery slides under the little arm and is held against the board), you are doing it correctly. You want solder mask openings for those three pads but do not want a paste mask opening for the center, circular pad, just the two square pads.

2) The solder mask layer shows where you have openings in the solder mask. The openings are usually a bit bigger than the SMT pads. The paste mask shows where you want solder paste deposited. It's usually a little smaller than the SMT pads. When you get the boards from a PCB fabrication house the paste mask layer will not be applied yet. That will happen when the board is being assembled. A machine will deposit solder paste in all of the paste mask openings, the parts will be deposited in the correct locations with the pins sitting on the solder paste then it will go through an oven where the solder will re flow.

3) How we do it is a drawing (PDF is always safe) of the assembly with instructions on how, what and where to solder things to a finished assembly is given. You can ask whomever you are having build the boards what they would prefer. It's something you'll have to make yourself rather than a file that's automatically generated by your PCB software.

4) If that is an issue just make large enough SMT pads so the wires can be soldered to one side of the board rather than through a hole.
 

TheMaster

Jul 20, 2016
47
Joined
Jul 20, 2016
Messages
47
The way the outer layers of a PCB work is there is the layer of copper, which consists of your pads, traces and fills. Then there's a layer of soler mask, which is the (typically) green stuff that covers most of the copper and prevents solder from wicking from the pads to the traces and gives some degree of protection. Then they give the exposed pads some sort of protective coating to prevent oxidation (usually gold, silver or solder). With that in mind:

1) SMT pads are just areas of copper that do not have solder mask over them but do have the protective coating. If I'm understanding that part correctly (the battery slides under the little arm and is held against the board), you are doing it correctly. You want solder mask openings for those three pads but do not want a paste mask opening for the center, circular pad, just the two square pads.

2) The solder mask layer shows where you have openings in the solder mask. The openings are usually a bit bigger than the SMT pads. The paste mask shows where you want solder paste deposited. It's usually a little smaller than the SMT pads. When you get the boards from a PCB fabrication house the paste mask layer will not be applied yet. That will happen when the board is being assembled. A machine will deposit solder paste in all of the paste mask openings, the parts will be deposited in the correct locations with the pins sitting on the solder paste then it will go through an oven where the solder will re flow.

3) How we do it is a drawing (PDF is always safe) of the assembly with instructions on how, what and where to solder things to a finished assembly is given. You can ask whomever you are having build the boards what they would prefer. It's something you'll have to make yourself rather than a file that's automatically generated by your PCB software.

4) If that is an issue just make large enough SMT pads so the wires can be soldered to one side of the board rather than through a hole.
Thank you so much for taking the time to write that out. You have truly done your good deed of the day sir.
 

Colin Mitchell

Aug 31, 2014
1,416
Joined
Aug 31, 2014
Messages
1,416
It is best to get a $5.00 prototype made and sent to the person who is going to produce the final product.
I have had some dreadful mistakes by Chinese who hold your drawings up-side-down and produce a backward result.
They never compensate you.
 

Elizabethpcb

Dec 8, 2016
1
Joined
Dec 8, 2016
Messages
1
Maybe you could try PCBWin to go through your mass production, I have boughted from their website, their quality is good, their 1L board is very cheaper.
 
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