1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Do off axis traces pull surface mount parts out of line?

Discussion in 'Circuit Simulation & PCB Design' started by Triode, May 8, 2017.

  1. Triode

    Triode Member

    Joined:
    Feb 11, 2009
    Messages:
    925
    Likes:
    22
    Location:
    Bay Area
    I was taught early on by an electrical engineer who trained me that when you design a PCB for surface mount parts that it is not required but best practice to have traces aligned such that the flow of solder will not pull them out of place. Most often this would mean having the trace into the pad come in line with the part. Or if it is connected to more that one trace, to place them symmetrically.

    Now I work with a lot of electronic engineers, and they don't seem to care about this and it doesn't seem to cause problems. I've seen people place 0201 (0603) sized resistors with both traces coming off sideways with the same twist, and not only did no one mention it in the board review, it didn't cause any manufacturing issues at all.

    I'm wondering, is it that modern solder mask, placement, or reflow soldering doesn't have this problem, or are they just getting away with it? I don't want to be taking up space to stick to a design rule that turns out not to matter. Some of my designs have hundreds of tiny surface mount components on them, so I also don't want to drop that rule if it does matter. I see that Altium's guide to PCB design mentions this rule, but the design guide of our manufacturer, express manufacture inc., does not mention it.

    This question is not crucial at the moment since it appears that no one has a problem with me always places traces in line with the axis, and they also don't care if I don't, but I want to keep with best practices when I can.
     
  2. RadioRon

    RadioRon Well-Known Member

    Joined:
    Oct 7, 2005
    Messages:
    1,755
    Likes:
    53
    Location:
    BC, Canada
    It seems logical that when you are using a solder mask and all traces leaving the pad are under this mask, then solder won't flow off the pad and so the component won't be pulled out of alignment. Perhaps the design rule only applies to boards without solder mask or to boards where the solder mask opening is much larger than the pad.
     
  3. Triode

    Triode Member

    Joined:
    Feb 11, 2009
    Messages:
    925
    Likes:
    22
    Location:
    Bay Area
    That makes sense to me. With a good professional solder mask, I don't really see a way the solder could be affected much by the traces coming into the pad since the solder cannot flow down them. But my mentor may have been referring to his experience in home-etched boards, of which he made many.
     

Share This Page