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Circuit Board Topside Assembly Instructions

PCB Topside Bare Board

PRO-KIT_01_TOPSIDE INLUSTRATION

Equipment, Supplies, and Components Required

Equipment Required
Safety Glasses
Soldering Iron / Soldering Iron Stand / Wet Sponge
Rosin or No-clean Flux Core
Diagonal Wire Cutters

Components Required
12 Blue 5mm LED's
88 Red 5mm LED's
128 White 5mm LED's

Important Please Note: 

Red, white, and blue LEDs are polarized components, meaning they must be installed in the correct orientation within a circuit to function properly.

Refer to the printed circuit board (PCB) assembly illustration and assembly instructions below for the correct LED locations, and orientation.

For through-hole LEDs, the primary way to determine which lead is the anode, and which is the cathode is the length of the lead. The anode will always be the longer of the two leads, and the cathode will always be the shorter of the two leads. 

A secondary method to identify the anode and cathode leads in through-hole LEDs is that many manufacturers design the LED's plastic housing with a flat edge on the side closest to the cathode lead. (Shown below). However, this method is less reliable, as not all manufacturers include a flat edge to indicate the cathode side, and the edge may be subtle and difficult to see without magnification.

Circuit Board Topside LED Location & Orientation Guide

FLAG PCB TOPSIDE ELECTRICAL LAYOUT
FLAG PCB TOPSIDE COMPONENT LAYOUT
led orientation
LED Orientation

R1 circuit, circuit board illustration depicting circuit board features 

Test Circuits Soldering Blue

R1 Circuit Example Assembly Instructions

Test Circuits 1.

Example R1 Circuit After Soldering

led test circuit

IPC Class- 2 Acceptability Criteria for Lead Soldering to Rectangular Pads

​1. General Requirements (IPC‑A‑610)

  • Wetting: Solder must wet both the pad and the lead, with smooth flow and no voids.

  • Fillet Shape: Concave fillet preferred, tapering from the pad up the lead.

  • Coverage: Solder should cover the pad fully, with no exposed copper.

  • Cleanliness: No solder balls, bridging.

​​

2. Lead‑to‑Pad Joint Criteria

  • Lead Contact: The lead must lie flat against the pad surface, with no lifting or gaps.

  • Fillet Length:

    • Minimum solder fillet length should extend to at least the end of the lead.

    • For Class 2 assemblies, solder should extend slightly beyond the lead end for mechanical strength.

  • Fillet Thickness:

    • Solder thickness should be sufficient to bond but not excessive (no “bulbous” joints).

  • Defects:

    • No voids under the lead.

    • No insufficient solder (bare pad areas).

    • No cold joints (dull, grainy appearance).

 

3. Inspection Criteria (IPC‑A‑610, Surface Mount Section)

  • Acceptable Joint:

    • Lead flat on pad, solder fillet visible along sides.

    • Smooth, shiny solder with full pad coverage.

  • Defective Joint:

    • Lead lifted or not fully wetted.

    • Solder only partially covering pad.

    • Excess solder obscuring lead outline.

    • Bridging to adjacent pads.

Additional Example Circuits R12 & R13

test circuits

General Procedure for:
Installing, Crimping, Trimming, and Soldering Through-Hole LEDs

Materials Needed:

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  • Safety glasses

  • Through-hole LEDs (Red, White, Blue)

  • Circuit board (PCB)

  • Soldering iron and solder

  • Wire cutters


1. Identify LED Polarity

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  • Anode (+): Longer lead

  • Cathode (–): Shorter lead, often marked with a flat edge on the LED casing

  • Check the PCB for polarity markings "-" near the holes.


2. Orient the LED Correctly

​

  • Insert the anode the long lead into the hole without a marking.

  • Insert the cathode into the hole marked with a "–" sign.


3. Seat the LED

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  • Insert the LED into the designated holes on the PCB until the bottom edge of the lens sits flush with the top surface of the board.

  • While holding the LED firmly in place from the top side, use your fingers to bend each lead outward at a 90-degree angle on the underside of the PCB. Bend the leads in the direction of the rectangular soldering pads, ensuring each lead overlays the pad as close to the center of the pad, and as close to the board surface as possible.

  • This manual bend secures the LED in place, keeping it tightly flush against the circuit board and preventing any movement during soldering.

  • Trim the excess length of each lead so it does not extend beyond the soldering pad, allowing for a clean and reliable solder joint. (Important Safety Note: When trimming LED leads to proper length, secure the section of lead with one of your fingers, or small pliers, as to not allow the lead to fly-off when being cut and hit someone in the face.)


5. Solder the Leads

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  • Heat the pad and lead simultaneously with the soldering iron

  • Apply solder until it flows and covers the pad and lead

  • Remove the iron and let the joint cool.

  • Avoid cold solder joints (dull or cracked appearance)

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7. Inspection​

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  • Visually inspect your solder joints for defects, rework as needed.

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8. Electrical Testing

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  • After completion of fully populating/assembling and soldering of all LEDs, proceed to electrical testing to validate functionality of all LEDs. Troubleshoot, rework and repair as necessary to obtain a 100% fully functional circuit board. 

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