It's common these days to need to replace obsolete DIP chip parts in vintage electronics with small PCBs that fit where the DIP chips used to go. For instance the infamous SID and PLA chips in Commodore computers.
However the most common types of pin headers available to make the legs are actually too thick and they damage DIP sockets. This includes common machined round pins, which are thinner than the square pins, and ok for use in round sockets, but still technically a bit too thick for leaf sockets. They can compress the wipers and make the socket no longer make a good connection with a real DIP chip any more. Also those pins always have a quite large insulator & shoulder, and in some cases there is not much room where a DIP chip came out of for that much vertical thickness of the pin header shoulders and insulators plus the pcb plus the components soldered to the pcb.
Here are 3 different ways to make DIP legs on PCBs, where the legs are thin enough not to stretch out leaf/wiper style DIP sockets, and with little or no shoulder.
The hole size to use for the plated through holes for all of these is the same, 0.6mm or 24mils. This is intentionally a bit too small to accept normal machined pins, and also helps hold the legs a bit straighter while soldering.
Some example projects, including KiCAD sources, that use these methods for legs:
https://github.com/bkw777/aDIPters
https://github.com/bkw777/Model_T_RAM
https://github.com/bkw777/TANDY_200_RAM
TE Connectivity 1544210 SIL leadframe
Cut the "busy" ends off the legs with scissors, leaving a simple "comb" of legs.
Drop that comb down from the top, leaving about 4mm of leg extending from the bottom.
Solder, then cut the tops off flush.
This option doesn't require much explaination or special technique, you just buy the pins and solder them. One suggestion is to use a machined round style DIP socket or two single-row female headers inserted into a breadboard as a jig to hold all the pins in alignment while soldering.
Sources
DigiKey: Mill-Max 3121
Mouser: Mill-Max 3121
DigiKey: Mill-Max 5421
DigiKey: Keystone 1378
Mouser: Keystone 1378
First you need to find a source for actual brass wire instead of brass colored aluminum wire.
This kind of wire is usually sold for making jewelry, and the sellers do not write their descriptions with electronics in mind, so it takes careful examination to tell suitable products from unsuitable ones.
There are many small vendors that sometimes have this kind of wire, but the sellers come and go and their stock comes and goes.
Also prices vary quite a bit, so don't necessarily buy the first thing you find even if it does meet the specs.
Start with a basic search for gold-plated brass wire .
You want wire that has the following properties:
- solid brass
- 26 gauge / 0.4 mm
- half-hard temper
- gold filled / gold plated
- round
- 1 foot length or more
- no "tarnish resistant" coating
A few example sources:
wirejewelry.com
etsy StirlingSilverBox
etsy AnniesLittleThings
There are many many products that look the same and have very similar descriptions in their listings.
You have to look over the descriptions carefully to make sure you don't get gold colored anodized aluminum wire with laquer coating, or real brass but with a soft temper.
Avoid anything with any of these terms in the description:
- soft, dead soft
- anti-tarnish, tarnish resistant
- colored, gold colored, golden
A single foot of wire provides about about 50 6mm legs that are:
- gold plated
- Similar strength/stiffness as ordinary chip legs
- malleable enough to survive being bent and straightened a few times
- small enough diameter not to stretch out sockets
You also need:
- a standard breadboard
- a 40 pin single row machined round female pin header
- painters tape
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Break the 40-pin stick of sockets in half to make 2 20-pin rows.
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Insert the two 20-pin sockets into the breadboard parallel to each other, 0.6 inches apart. (for a typical DIP-28 0.6 example, for Model T RAM the spacing is 0.7 inches)
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Cover the sockets with painters tape. This is to prevent solder from running down the leg.
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Place the PCB on top of the tape & sockets. Align the PCB with the sockets under the tape.
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Hold the roll or loop of wire in one hand, with the end of the wire in 2 fingers so that you can poke with it. It's hard to grip the thin wire strongly enough to poke through the tape. My technique is to hold the loop in my palm such that the wire comes off the loop and runs all along the full length of the underside of my index finger, and the end of my thumb holds the wire centered on the pad of my index finger, or the inside of the first joint. When pushing down on the wire, it's pushing really all along the length of my index finger. The extra friction plus holding the loop fixed in the same hand gives the stregth to poke with the end of the wire quite strongly.
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Poke the wire down from the top of pin #1, through the PCB, and punch down through the tape into the socket below, until the wire hits the bottom of the socket.
- If the wire catches on the edge of the socket, just back up your grip so you're holding the wire from about an inch above the board, lighten the downward force so you're only pushing down lightly, and wiggle the wire around a little. The hole in the PCB acts like a fulcrum and the wire will drop right in.
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While holding the wire bottomed-out in the socket, cut the wire flush with the top of the PCB.
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Repeat 6 and 7 for the opposite corner pin
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Solder those 2 corner pins.
10 Repeat 6 and 7 for all other pins. Just insert & cut, no solder.
11 Solder all other pins.
Done. Lift the module out of the sockets and discard the painters tape.
You don't have have to use a fresh piece of tape for each pcb, but one thing that can happen after a while is if you use flux it collects in the socket, and then when soldering the next pcb the pin heats up in the socket and boils the collected flux, and it bubbles up through the via and pushes the solder out and creates voids in the solder joint. So you want to either be careful to use only just enough flux to get the job done, or solder pins quickly so that the leg doesn't have time to heat up the socket.