How do you assemble a PCB?

PCB assembly is generally divided into two categories: Surface-Mount Technology (SMT) and Through-Hole Technology (THT), or a combination of both.

 

 

A complete PCBA is the core component of a product, often referred to as the brain of the product, controlling its essential functions. Therefore, the quality of the PCBA directly reflects the quality of the product. Under any circumstances, it is crucial to maintain the core functionality of the product, making PCB assembly highly important. In this article, we will explore how to assemble high-quality PCBA.

What is PCB Assembly?

PCB assembly refers to the process of assembling various electronic components and devices onto a printed circuit board (PCB) according to predefined circuit diagrams and design specifications. This process is a critical step in the manufacturing of electronic products as it determines their functionality and performance.

PCB assembly is generally divided into two categories: Surface-Mount Technology (SMT) and Through-Hole Technology (THT), or a combination of both.

Surface-Mount Technology (SMT):
SMT is a technique where surface-mounted components, typically without pins or with short pins, are directly placed on the surface of the PCB. It uses an automatic pick-and-place machine to precisely position the components on the designated spots of the PCB, and then a reflow oven heats the solder paste to melt it, establishing the electrical connection between the components and the PCB.

Through-Hole Technology (THT):
THT is a method where components with leads are inserted into the through-holes of the PCB and then soldered. This technique is typically used for components with longer leads, such as electrolytic capacitors and transformers. Soldering can be done manually using a soldering iron or through wave soldering equipment.

 

How to Assemble a PCB

I. Tools and Materials Preparation

Tools:

• Soldering iron (adjustable temperature, recommended 30-60W) or soldering station
• Solder wire (with flux core, diameter 0.6-1mm)
• Tweezers (fine-tip, bent-tip), diagonal pliers, wire stripper
• Desoldering pump or desoldering braid (for correcting errors)
• Multimeter (for continuity and parameter testing)
• Magnifying glass or microscope (to inspect fine solder joints)
• Anti-static wrist strap (when handling sensitive components)

Materials:

• PCB (pre-designed circuit board)
• Electronic components (resistors, capacitors, IC chips, etc.)
• Flux (optional, to improve soldering effectiveness)
• Cleaning agent (such as isopropyl alcohol, for cleaning post-soldering residue)

II. Pre-soldering Preparation

Review Circuit Diagram and BOM:

• Confirm component placement (refer to silk screen markings on the PCB, e.g., R1, C2).
• Cross-check component specifications (e.g., resistor values, capacitor voltage ratings).

Component Pre-treatment:

• Through-hole components (e.g., resistors, capacitors): Bend leads to fit the PCB hole spacing using pliers.
• Surface-mount components (e.g., SMD chips): Ensure leads are aligned and flat.

Clean the PCB:

• Use an alcohol wipe to clean the pads, removing any oxidation or contaminants.

III. Soldering Steps

1. Soldering Through-Hole Components:
   Order: Solder smaller components (e.g., resistors, diodes) first, followed by larger components (e.g., electrolytic capacitors, connectors).
   Method:

• Insert the component into the PCB, slightly spreading the leads on the backside to secure it.
• Apply the soldering iron tip to the pad and lead, feeding in solder to form a conical solder joint.
• Trim off excess leads (leaving 1-2mm).

2. Soldering Surface-Mount Components:
   Hand Soldering (for QFP, SOP packages, etc.):

• Apply a small amount of flux to the pads.
• Use tweezers to position the component, first soldering one pin to anchor it.
• Sequentially solder the remaining pins, avoiding solder bridges.

Hot Air Reflow (for BGA, QFN packages, etc.):

• Set the temperature (usually 300-350°C).
• Evenly heat the component until the solder melts.

3. Soldering IC Chips:
   Drag Soldering Method:

• Pile solder on one side of the pins, then drag the soldering iron tip across the pins, using surface tension to remove excess solder.

IV. Testing and Debugging

Visual Inspection:

• Check for cold joints, shorts, and correct component polarity.
• Use a magnifying glass to inspect the solder joints for smoothness.

Continuity Testing:

• Use the multimeter’s “beep” mode to check for shorts between power and ground.
• Verify that key signal lines are connected.

Power-On Testing:

• Connect the power supply (optionally in series with a current meter) and observe for any abnormal heating or smoke.
• Sequentially verify that each functional module operates correctly.

V. Precautions

Static Protection:

• Wear an anti-static wrist strap when handling MOSFETs, ICs, etc.
• Avoid touching the leads of sensitive components with bare hands.

Soldering Techniques:

• Keep the soldering iron temperature between 300-380°C (higher for lead-free solder).
• Limit heating time for each joint to no more than 3 seconds to prevent pad damage.

Safety and Maintenance:

• Work in a well-ventilated area to avoid inhaling harmful fumes.
• Turn off the soldering iron when not in use to prevent oxidation.

 

Shinelink's PCB Manufacturing

In today’s high-tech world, as engineers continue to pack more data and power into ever-smaller chips, printed circuit boards (PCBs) are becoming increasingly complex. As computing and electronic devices shrink, the PCBs that power these devices and connect them to wireless networks are also becoming smaller. For PCB manufacturers, this means that the production of printed circuit boards will require advanced engineering technology. To ensure PCBs meet current standards and function efficiently, manufacturers must have properly specified bare PCBs to facilitate each step of the assembly process. At Shinelink, we use the latest technology in our own factory to complete each bare PCB order according to customer specifications. For more information on PCB manufacturing, please contact Shinelink.