Circuit Building 101

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Intro: Circuit Building 101

This is a beginner's guide to building circuits that will talk about the "proper" way to install components (resistors, ICs, capacitors, etc), and also a little bit about soldering. It'll cover things like recommended tools, how far and which direction components should be inserted, pre-bending and clinching leads along with some tips and tricks. We'll be using a power supply kit made by David at uCHobby.com that plugs into a bread board for demonstration. Yep, we're commercial and sell all this stuff, but the advice should apply equally well to anyone's tools and circuits.

Step 1: Recommended Tools and Supplies

- Soldering iron and solder: Just about any 25-30 Watt soldering iron will do. Ideally, the temperature of you iron would be between 600-700 degrees F (for lead-free solder, 700-800 is recommended). How temperature relates to wattage depends a lot on the iron (watch a video testing the temperature of cheap RadioShack irons), and some high wattage irons have too high of a temperature. Avoid "solder guns" as these are meant for pipe soldering. Not only can these be too hot, but they work by running high current through a resistive heating element, and this could apply dangerous voltages to your circuit.

For solder, we recommend starting out with a lead-based solder, usually called 63/37 (63% tin, 37% lead by weight) or 60/40 rosin cored solder. Get whatever's cheaper; there's unnoticeable difference in hand soldering between 63/37 and 60/40. The rosin is a flux that cleans parts so solder will bond with them. Avoid solid wire (no flux core) and acid cored solder (for plumbing, too aggressive for circuits). We recommend solder that's about .031" in diameter for most through-hole components. Water-soluble flux is much more aggressive than rosin, and these residues must be cleaned. Lead-free solder melts at a higher temperature, and doesn't wet or spread out as readily, so it will be slightly harder to use.

- Needle Nose Pliers: Useful for pre-bending leads, pulling out components during de-soldering, and a lot of other things.

- Wire Strippers: Two types are shown: the yellow ones can be adjusted to strip any size wire (good for small 28-30 AWG ribbon cable wires) whereas the red handled ones have several fixed hole sizes.

- Flush Cutters: Used to trim leads close to the board after soldering .

- Clamps: Oftentimes just resting your board on a table will be fine, but the clamps are especially helpful when desoldering parts or soldering wires together.

- Solder Sucker and Solder Wick: Both are inexpensive ways to remove solder. The sucker is a spring loaded tube that vacuums out solder and the wick is a fine braid of flux coated copper that soaks up solder.

- Multimeter: Some multimeters have a continuity check that beeps if there is a complete circuit. This is very useful for making sure parts are connected or disconnected when there're a lot of wires and parts.

-Pink Erasor: (not shown) A pink eraser can be used to rub off oxides from older components and boards without risking damage to the parts.

Step 2: What Order and Which Way to Insert Components

Most people advise to start with the shorter components first, and add more by height from there. This has two benefits:

- If there are tall components right next to shorter ones, you avoid having to bend already-installed taller components out of the way while inserting shorter ones later on.
- One of the best ways to hold a component in place is to insert it, and then lay the board upside down so the table surface keeps the component in place. If you install shortest to tallest, the tallest component will always be the one you're currently working on.

It's also helpful to install components so that the value can be read in the same direction as the surrounding text. For instance, install all the resistors with their tolerance bands on the right so that all the values can be read without having to rotate the board.

Make sure the notch on ICs matches the notch on the board.

Step 3: Prebend Leads for Easy Insertion

To avoid stressing the holes and junction between the resistor body and its lead, pre-bend the leads before inserting the part. To do this, line up the resistor on it's board location, grip the lead a little inside with needle nose pliers and then fold the lead over the pliers. The pliers prevent stress from reaching the the connection point between body and lead. You can also use something called a christmas tree to quickly form both leads to the correct size.

Just fyi, for sensitive circuits (ie, military, space), serrated pliers aren't allowed because they might create a divot in the lead that could weaken and fail from vibration.

The "right" way aside, just bending the leads with fingers can work well, too

Step 4: Clinch Leads to Hold Parts in Place While Soldering

Clinching means bending the lead slightly on the other side of the board to hold the part in place. For ICs, bend two opposite corners outwards.

The only downside is that parts can be harder to remove later. Other methods to hold things in place while you flip the board over include just having the table surface hold it in place, and also using tape. For instance, header pins can't be bent, so the table is used to hold them up in the last picture. You can also place some solder on one empty pad, and then reheat that pad while pressing the part through to get started.

In industrial manufacturing processes, parts are either held in place by a small drop of adhesive (for surface mount) or by clinching the leads. Boards are then transported via conveyor over molten fountains of solder (google wave soldering).

Step 5: Make Sure LEDs and Some Capacitors Are Inserted in the Right Direction

The longer lead on electrolytic capacitors (the cylinder ones) and LEDs is positive. Insert most components until they lie flat on the board for extra stability unless they have a metal casing that could cause a short circuit.

it's OK if the yellow plastic on ceramic capacitors (disc shaped) goes beneath the top level of the board and touches the solder, it just can't show through to the other side (according to IPC, the industry's soldering standards organization).

Step 6: Soldering

You've probably heard that solder should melted on the parts and not the iron tip. The catch is that a dry tip will not transfer heat very well. You need to have a little solder, called a heat bridge, between the iron tip and parts. Do this by either melting a small amount of solder on the tip before soldering ("tinning" the tip) or adding some solder at the junction between tip and work. Then melt solder on the opposite. It should spread out towards the iron tip and heat. A video is available with many more details.

Usually people say that joints should come out looking shiny, but this is only true for lead-based solder. Lead-free joints will have a duller surface finish, but still be perfectly fine joints. With either type, the solder should cling to or wet the surfaces, and not just sit on top of them. It should form a smooth ramp and feather out across the pad. The above link also has some galleries of good and bad joints.

It's a good idea to check the part for correct alignment after soldering one pin. Adjustments can easily be made at this point by reheating that one pin, but once multiple pins have been soldering, the part may need to be completely removed to adjust it.

Step 7: Trim the Leads

Flush cutters are useful for trimming leads close to the surface. Regular diagonal cutters can work, also. Safety goggles are actually a good idea for this step as the leads can fly off quickly. We usually like to hold on to the lead while clipping.

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    83 Discussions

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    LionBlood

    5 years ago on Step 7

    I want to learn how to make one. How do I make my own circuit, I don't understand how

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    mscharf

    6 years ago on Introduction

    Does anyone know a way of turning on and off a single led using a ir remote? What doe I need? I was thinking of some how connecting the led with the appropriate resister along with a IR Receiver Diode and some kind of switch and a power source, how would this work? Is this all I need? any and all help is greatly appreciated.

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    bahi

    8 years ago on Step 2

    Instructables covering the basics are very useful. Good work, thanks.

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    mic_hviid

    8 years ago on Introduction

    Nice tut! Thanks!

    Anyone knows how to remove some shiny black laquer often found on top of components, probably to obscure their make?

    Michael

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    raykholo

    9 years ago on Introduction

    actually the intro to this instructable states that it is simply about how to solder components to a pcb assuming it is already made industrially or home-etched. There are many other instructables and sources on the internet for how to do toner transfer and the "uv method" for etching in a home environment.

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    D.L.H.

    9 years ago on Introduction

    Helpful in basic understanding on building such a device glad you made it.

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    dowd95

    9 years ago on Introduction

    Well a circuit board is essentially a copper-clad board, usually made of fiberglass. When they make circuit boards they etch away all the copper except for where they want the traces, which connect the "holes" you speak of together.

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    im certainly no expert, but certain holes on the board are connected so any configuration of parts will not work. for your third question, yes you can do that but i wouldnt, it would make it very difficult. and your 2nd question, your could buy protoboard and use solder to create your own circuits, or buy a very expensive machine to do it, also you could possible use paper and conductive ink but im not sure how far you could possibly go with that. (and if im wrong about anything, somebody please correct me)

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    yusaku

    9 years ago on Step 7

    clinching should only be done if absolutely necessary, increases chance of lifting pads amongst other issues most parts can be tacked in place while holding the part in.

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    ac-dc

    10 years ago on Step 1

    There is a noticable difference between 63/47 and 60/40. 63/47 being eutectic is much easier to use because the part doesn't have to be held perfectly still while the solder goes through it's plastic stage while hardening.

    Acid core is not too aggressive for circuits, in fact for aged parts it is the preferred solution but it absolutely must be completely cleaned off later. In fact, with today's lead free soldering the industry is using more aggressive fluxes than the old rosin core was, BUT for a hobbyist using new parts I agree rosin core (or no-clean, depending on the project requirements) would be the best choice for typical soldering.

    Another *tool* to have is liquid flux. Usually, people apply too much solder to a joint just trying to get enough flux on to make it flow good. There are solders with 3% flux instead of 1 or 2% that will do better or using a separate liquid flux will be the best result. Liquid flux also is very handy when using desoldering braid, allowing excess solder to be removed more quickly and gently by reducing the amount of heat applied, even if the braid had a little flux in it already.

    Solder guns do not apply dangerous voltages to a circuit. Not possible. They use an isolating transformer and very low (isolated) voltage. However they are too hot running for most hobbyist electronic work and yet for some jobs, there is no way a 25-30W iron would get the job done so either a heftier iron with stouter tip or a gun would be required.

    4 replies
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    bobheckac-dc

    Reply 9 years ago on Introduction

    You guys are really talking about 63/37, not 63/47. Beginners may get confused.

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    ac-dcbobheck

    Reply 9 years ago on Introduction

    Thank you for that correction, yes since they are percentages, 63% + 47% = 110 (%) would be impossible, I must've been half asleep when I posted that.

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    As far as I know, the main impetus to switch to 63/37 was for mass manufacturing of SMT devices, not easier hand soldering. Yep, 60/40 has a plastic state, but I personally have not experienced greater freezing time, more disturbed or cold joints, or significantly improved flow of 63/37 over 60/40. One thing that usually isn't mentioned when talking about eutectic alloys, is that a cup of water is eutectic (meaning it's all water or all ice above and below some temperature), but if you put it in the freezer, it doesn't all freeze instantaneously; rather, it freezes from the outside in. The question to answer is, "How much faster does complete freezing occur?" I wonder if anyone's ever done a blind study to see if people could guess which solder they were using. This isn't necessarily for you, ac-dc, but anyone else wading through these comments that wants to learn what eutectic means can visit that link (click expand after alloy, and then click expand again in the "Standard lead-based solder" section).

    I could be wrong on this, but doesn't "acid-core" usually refer to copper pipe solder? I'm used to seeing "water-soluble" as the electronics version that is certainly safe to use if it's cleaned thoroughly.

    Good stuff about using liquid flux with braid.

    On solder guns, I guess the first question to answer is "How much voltage could damage a circuit?" The Weller WES51 brags about having a grounded tip with 2 mv RMS or less voltage, and also zero power switching. What kind of a circuit would be affected by, say, 5mV? 20mV? 1V? Certainly the solder guns don't have 120V at the end, but I'd bet it's in the single digits... correct me if that's off.

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    If by impetus you mean simply that mass manufacturers are the majority using solder then yes, but it doesn't diminish the benefits of eutectic solder for DIYers hand soldering. Acid-core refers to acid-core, it is not just "copper pipe" you can use on anything you want, including stained glass or due to it's more active nature, exceptionally corroded parts. The problem with it isn't so much the effect on the metal while soldering, as the solder does plate those parts but rather than when it's left on an area it just continues to slowly eat away at it so it must be cleaned off. Personally I find it very handy to use plumber's tinning flux to plate homemade PCBs, since it's readily available, the price is great, and I've never had a problem with it though I do clean off excess flux right after soldering. A soldering gun does not have much voltage, single digit at most IF the tip weren't installed, but it is which pulls down the voltage to practically nothing relative to itself - but you are ignoring the important part - there is no circuit, it's not a voltage relative to anything on the work, only relative to an inaccessible point in the soldering gun itself. With the resistive element being driven by secondary winding of a transformer, it's floating - the only way you would put current through the work is if you soldered a second wire to the inside of the soldering gun then touched that somewhere else on the work.