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I've ordered a PCB to be manufactured, I now need to solder some resistors and transistor to the board.

enter image description here

The transistor is a 2N3904 and it's place on the board is Q1. As can be seen the pins are aligned in triangular arrangement with the middle leg offset. Is this a special type of transistor because all of the components for this part which I have found online appear to have the legs in a straight line. Or is it simply a case of bending the legs to make them fit.

Apologies if this is a dumb newbie question :)

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3 Answers 3

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The only dumb question is the unasked one

You just bend the pins to make them fit ;)

It's actually possible to get the transistors with the legs pre-bent, but if you're only making one or two boards, of course there's no point to bother with that.

It's actually going to be much easier to solder the pins with them spread out like this. While having a footprint with them 'straight', they end up very very close together and can be tricky for a rookie solderer to do w/o bridging solder between pins.

The "ideal" method of bending would be to grasp all 3 pins with tweezers at the point they enter the plastic body, and hold tight, then use your fingers to bend them to fit. The reason you would want to do this, if you don't hold the pin-to-plastic junction still, you can crack the plastic. Unlikely but does happen. Same goes for the resistors on your board too. Let the metal pin take all the bending stress, not the component body.

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    \$\begingroup\$ Appreciate the additional tips, and good point about being easier to solder, I need all the help I can get :) \$\endgroup\$
    – Alan A
    May 4, 2023 at 13:53
  • \$\begingroup\$ I've also seen transistors with the legs pre-spread-out to a 0.1" pitch (or whichever one is the standard) \$\endgroup\$ May 5, 2023 at 2:20
  • \$\begingroup\$ I can still remember when you could get a job as a lead bender. Full time work bending leads to resistors, transistors, etc. to be fitted into PCBs later. \$\endgroup\$ May 5, 2023 at 14:26
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In terms of what you need to do, the answer from Kyle B says it all.

I just wanted to give some additional background context and mention that there are many package styles for transistors, and some of them so have the pins arranged in a triangle (matching the holes shown on your PCB image).

transistor styles

These are some examples of the offset pin style. These are NOT the same transistor as your part and you should not switch what parts you are using; I just found random examples of other parts that show the other styles.

metal case with offset pins

https://mou.sr/3LB3dTF https://www.mouser.com/ProductDetail/Central-Semiconductor/2N2270-PBFREE?qs=u16ybLDytRb1HLZnB7wW3w%3D%3D https://www.componentsinfo.com/wp-content/uploads/2021/12/2n2222-metal-can-transistor-pinout-2.gif

These may be less common, and they often have a metal casing instead of plastic.

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You'll need to bend the centre pin to fit, or alternatively bend all the pins half as much. As an aside, your PCB screenshot doesn't appear to have any holes. Please make sure you've generated a drill file and passed it on to the fab you're using, otherwise you'll have a bad time.

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