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I've seen some PCB's with components mounted at multiples of 45 degrees (45, 135, etc.) I recently discovered my PCB program (gEDA PCB) supports these, though it isn't a GUI function and you have to run a command. When is it appropriate to mount at these angles? And what about angles of 30 degrees and 60 degrees, or arbitrary angles?

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7 Answers 7

up vote 12 down vote accepted

Another reason would be for indicator or display components. It's not terribly uncommon to see chip LEDs at varying angle to fit the aesthetics of a particular device.

Whatever the reasoning, most SMT machines can places parts at angles without issue.

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Thanks for your answer. Please see the FAQ about signatures, they are generally not allowed, your userpage is the place for them. –  Thomas O Nov 1 '10 at 21:23
    
+1 aesthetics: Paul Pounds "LED pocket watch" just wouldn't be the same without arbitrary-angle rotation of each of those little LEDs. –  davidcary Apr 7 '11 at 0:01
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Placing a QFP chip at 45 degrees can make it easier to connect the leads to pins on a DIL board. Try it for yourself. Other angles aren't helpful.

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I've actually seen arbitrary angles on a motherboard before. The RAM sockets were mounted at about 15 degrees in the middle of the motherboard (not a high performance computer, it was designed to be small.) –  Thomas O Nov 1 '10 at 20:39
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a picture's worth a thousand words! –  stevenvh Jun 3 '11 at 16:44
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Parts can be at whatever angle they need to be to help layout or fit into some bizarre package. Your manufacturing engineer may not like it, but if it's required, then oh well. As Duane mentions, this is rarely a problem nowadays, but be sure.

Conversely, your manufacturing engineer will pretty much demand 45° rotation of QFPs if they are to be wave soldered.

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How would you wave solder a QFP? It's a surface mount package. Do you mean PLCC sockets? –  pingswept Nov 1 '10 at 22:18
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@pingswept: No, TQFPs up to 100 pins can be wave soldered, doesn't really answer "how", but NXP has guidelines nxp.com/documents/wave_soldering/QFP-SQFP-TQFP-WAVE.pdf Some paste alloy I used a while ago (SN100C) touts this ability as one of it's strengths dklmetals.co.uk/PDF%20Files/SN100C.pdf . I don't know enough to extol the virtues of wave soldering, but I assume it's preferable to reflow in some cases. –  Nick T Nov 1 '10 at 22:23
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Fascinating. All the wave soldering I've seen has been on the underside of a board with through-hole components on the top. But, the first PDF you linked to definitely references wave soldering QFP components. I can't imagine why the plastic package doesn't melt as you run it through the solder wave. Anyone know how this works? –  pingswept Nov 2 '10 at 0:13
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Wave solder temp won't be much different to reflow, and may actually be exposed for less time. A particular issue is the higher rate-of-rise which can cause popcorning damage due to trapped moisture, but it would take a lot more to melt the plastic used for IC packages. –  mikeselectricstuff Nov 2 '10 at 0:32
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Ha! The layout program specified (gEDA PCB) doesn't support rotating a square to 45 degrees. The thermal pad of a QFN is usually a square. Rotating it at 45 degrees doesn't work.

One workaround is to make it a not-quite-square.

You will also encounter another problem with gEDA PCB: text cannot be rotated to arbitrary angles. Only 0,90,180,270 degrees.

I don't recommend PCB for anything other than simple rectilinear designs.

edit: I have been using pcb for increasingly geometrically complex designs, and it gets harder and harder. Finally, I made a script to convert DXF to pcb's format, such as it is.

The script is here: http://vivara.net/software/dxftopy.tar.gz

It goes from qcad:

alt text

To pcb:

alt text

Resulting file (ben-mode render):

alt text

But this process is an unspeakable pain in the hindquarters. pcb is terrible at editing anything that is not on a grid.

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Uhm, it can. Try the command ":FreeRotateBuffer(45)" when something is copied into the buffer. You need a new version to do this (I have 20091103), but it does work with squares. I do wish it were broken out to the UI though. –  Thomas O Nov 2 '10 at 7:51
    
Yup - you can rotate footprints to arbitrary values, you can even rotate less than a degree, If you want text at an arbitrary angle you can import a converted Postscript file, GEDA PCB can be very powerful and versatile and does far more than just "simple rectilinear designs" - if you can be bothered to learn it –  Jim Nov 2 '10 at 12:49
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I am familiar with the PostScript converter. I wrote it. –  markrages Nov 2 '10 at 14:43
    
Here's why squares rotated at 45 degrees don't work in pcb. pcb.gpleda.org/pcb-cvs/pcb.html#ElementLine-syntax Lines are marked by their start and end points, and the line width. A square is a line with identical start and end points. Therefore, the orientation of the square is not able to be captured by the file format. –  markrages Nov 2 '10 at 14:59
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Only Pins, Pads, ElementLines and ElementArcs are allowed within Elements. No Polys. Therefore a rect or poly will not work. Nor will a poly clear soldermask, if you were thinking about faking it that way. –  markrages Nov 2 '10 at 17:16
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When is it appropriate to mount components at a 45 degree angle?

Whenever you feel like it. Whenever it helps the layout. Don't stop at 45 degrees, use any angle that makes sense. Here's a board using 30 degrees.

Board using 30 degrees

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Inductors and magnetics that may generate fields are recommended to be offset from one another. As an example, don't line up L1, L2 and L3 next to each other. Place L1 as you normally would, L2 at right angles to L1 and L3 at a 45 degree angle. I took this example directly off a datasheet but forget whose (Microchip, I believe).

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When you want to wave solder (not much done anymore) QFP parts you simply have to place them at a 45 degree angle. If you place them orthogonally the solder wave will short all the pins transversal to the wave. 45 degrees allows to place solder thieves that take any excess solder.

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