Why aren't components in DIP package shipped with straight pins?

I've noticed that all DIP packaged devices have pins which are at an angle other than $90^{\circ}$ and need to be bent so that the angle is right for insertion into holes on the PCB or wherever.

Is there any reason other than tradition for that? I imagine that in most cases components are machine-inserted into their sockets or PCB holes, but why would it matter to the machine if the pins are bent or straight.

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As a human, I've always found it useful that the outward pressure holds the chip in place in a through-hole PCB, allowing me to flip the board over and solder the legs. –  Toby Jaffey Sep 21 '11 at 20:25
I doubt chip manufacturers do anything for the sake of "tradition". Every little detail has a purpose, even if it's not obvious. Remember they make millions of these, and every fraction of a cent counts. –  endolith Sep 21 '11 at 21:28

I'm pretty sure that auto-insertion machines expect to set pins to the desired orientation by pushing in on them from the outside. If the part is gripped from the outside and squeezed just far enough for the pins to enter the holes while the part is being squeezed, the elasticity of the pins will usually cause it to "grip" the holes as soon as they're released. Such gripping behavior may help keep the parts from being dislodged before wave soldering is complete.

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I forgot about that aspect of it! I haven't used DIP components in more than 15 years. –  user3624 Sep 21 '11 at 21:15

No matter how accurately they are bent into 90 deg. at the factory, they will get messed up during shipping and handling. So, no matter what, pins will have to be bent back to 90 deg during insertion. And it is easier to always bend pins in one direction than to bend some pins this way and other pins that way.

Let me explain better... Let's say that if a pin is bent 0 deg then really the pin is not bent at all and it sticks straight out and not down. When a pin is bent in shipping/handling it will be bent a max of + or - 10 deg. (I made up that number, but you'll get the idea.) If the pin was originally bent to 90 deg then some pins might be at 80 while others are at 100 deg. So, during insertion some pins would have to be bent IN while others would have to be bent OUT in order to line up with the holes or sockets.

Bending some pins in and others out is difficult to do with a robot. Yes, it can be done, but there are better ways. If the pins were originally bent to 75 deg instead of 90, then after shipping and handing some would be at 65 while others at 85 deg. Then the pick and place machine would only have to bend pins IN-- making the machine much simpler.

To make things better, bending pins IN is easier than bending pins OUT. That's because the same "hand" that grabs the parts only has to squeeze a little harder to bend the pins in. To bend pins out would require a little more work.

I should mention that this point before I get hate mail... The pick and place machines for SMT are frequently differently than TH (through-hole). SMT uses a vacuum system to pick up parts. TH machines could use vacuum for some things, but typically not. Also TH machines often have a device on them called a "lead former". These are normally used to bend and/or cut the leads on resistors, caps, and other devices. I'm sure that there is some machine out there that uses the lead-former to straighten DIP pins rather than using the "hand". But the same issues apply.

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Another issue is that there's a certain amount of backlash when bending pins. If a pin is bent to a certain angle and released, it will spring back a little bit. If one has a chip with pins are bent unevenly, straightening them will either require using trial and error for each pin, or bending all pins considerably to one side and then back toward the desired angle. If it's going to be necessary to bend all pins out enough to ensure consistent backlash behavior, why not just fab them that way? –  supercat Sep 21 '11 at 22:32