The IC package used most on perfboard is the DIP (Dual In-line Package), with pins in two parallel rows. The pins are thick and spaced 2.54 mm apart, so it plugs straight into perfboard holes. But mistakes like inserting the IC backwards or misreading pin numbers are very common, and once you get it wrong, the IC can heat up and be ruined. This article covers how to read DIP IC pin numbers, where the power pins are, and why and how to use sockets.
Finding the notch and pin 1
One end of the IC body has a half-circle notch cut into it, and there is often a small dot (circle) stamped next to pin 1. At least one of these two is the orientation marker.
- With the notch at the top, looking down from above, the upper-left pin is pin 1.
- Numbers go down the left row (1, 2, 3, …), then at the bottom cross to the right row and go up. That is counterclockwise.
- On a DIP-8, pin 8 is the upper-right pin; on a DIP-14, pin 14 is.
On perfboard, the notch is often laid on its side to the left. In that case the lower left is pin 1, the bottom row runs 1, 2, 3… toward the right, and the top row continues from right to left. The Patterndo editor also puts pin 1 of an IC on the left based on the component side, and automatically flips left and right to show the copper side. For the mirroring between the component side and copper side, see Reading a Layout Diagram.
Power pin positions
On most logic ICs, the last pin is VCC and the middle pin (half of the last) is GND. But there are exceptions, so the rule is to check the datasheet.
| IC | Type | VCC (+V) | GND |
|---|---|---|---|
| 74LS00, 74LS04, 74LS08, 74LS32, 74LS74 | 14-pin logic | 14 | 7 |
| 74LS47, 74LS138, 74LS139, 74LS151, 74LS157 | 16-pin logic | 16 | 8 |
| 74LS245 | 20-pin bus buffer | 20 | 10 |
| 74LS90 | 14-pin counter | 5 | 10 |
| CD4011 | 14-pin CMOS | 14 (VDD) | 7 (VSS) |
| CD4511 | 16-pin CMOS | 16 (VDD) | 8 (VSS) |
| NE555 | 8-pin timer | 8 | 1 |
| LM358 | 8-pin op-amp | 8 (V+) | 4 (V−) |
| LM324 | 14-pin op-amp | 4 (V+) | 11 (GND) |
The 74LS90 is 14 pins but its power is on pins 5 and 10, so people who memorized "pin 14 is +V" get it wrong most often. For the same reason, always check the datasheet pinout when using a new IC (see How to Read a Datasheet).
Why use an IC socket
Rather than soldering the IC directly onto the perfboard, we recommend soldering a socket first and plugging the IC in.
- There is no risk of the soldering heat damaging the IC.
- If you got the IC orientation wrong or it fails, it is easy to pull out.
- It is easy to modify the circuit or swap in a different IC.
- When pins are bent and do not fit the holes, the socket gives a reference.
Sockets also have a notch at one end. You must plug in the IC with the socket's notch and the IC's notch facing the same way. Precision sockets (round pins) make better contact, while low-cost sockets (leaf spring) are cheap but contact can loosen with long use.
Tips for soldering the socket
- Insert the socket into the holes and flip the board.
- Solder only two diagonal pins first (for example, pin 1 and the opposite end pin).
- Check that the socket sits flat against the board, and if it tilts, reheat and straighten it.
- Solder the remaining pins in order.
Tips for inserting and removing ICs
- Check that the pins line up straight, lay the IC on the desk and press one row slightly to bring the pins inward, then plug it into the socket.
- To remove it, use an IC extractor or a small flat screwdriver at alternate ends and lift one side a little at a time. If you pull hard on only one side, the pins bend.
- CMOS ICs (74HC, CD4000) are sensitive to static. Touch grounded metal before handling, and avoid touching the pins directly.
When you insert it backwards
If you insert an IC backwards, the VCC and GND pins end up in opposite positions and the power is applied reversed. The IC heats up quickly and can be permanently destroyed, so check the notch direction once more before powering up. If you turn it on and the IC is hot, cut the power at once and suspect the orientation first.
Ways to reduce orientation mistakes:
- On the same board, line up the notches of all ICs in the same direction.
- Mark socket pin 1 with a pen in small writing on the socket.
- Circle the notch direction on the layout diagram before soldering.
Summary
With the notch at the top, the upper left is pin 1 and numbers increase counterclockwise. The power pins are usually the last pin (+V) and the middle pin (GND), but there are exceptions like the 74LS90, so look at the datasheet. Solder the socket first and plug in the IC with the right orientation, and mistakes drop greatly. Next, see how to tidy IC power in Power Rails, Grounding, and Decoupling Capacitor Placement.