Modern printed circuit board (PCB) manufacturing requires efficient soldering techniques to accommodate increasingly complex electronic designs. Many electronic assemblies combine surface-mount technology (SMT) components with through-hole components, creating additional manufacturing requirements.
Pin-in-Paste soldering, also known as Intrusive Reflow Soldering, is a technique that allows compatible through-hole components to be soldered during the SMT reflow process. By integrating these operations, manufacturers can reduce separate soldering stages, minimize board handling and improve production efficiency.
Understanding the Pin-in-Paste process, its benefits, design requirements and limitations helps electronics manufacturers and OEMs determine whether this technique is suitable for their PCB assembly applications.
What Is Pin-in-Paste Soldering?
Pin-in-Paste (PiP) soldering is a PCB assembly technique in which solder paste is deposited into or around plated-through holes before through-hole components are inserted. The assembled PCB then passes through a reflow oven, where the solder paste melts and forms electrical and mechanical connections between component leads and the PCB.
Also referred to as Intrusive Reflow Soldering or paste-in-hole soldering, this method combines compatible through-hole component soldering with conventional SMT reflow assembly.
Unlike traditional wave soldering or selective soldering, which generally require separate soldering operations, the Pin-in-Paste technique allows suitable components to be soldered during the existing reflow cycle.
A typical Pin-in-Paste connector application involves inserting reflow-compatible connector pins into plated-through holes containing the required amount of solder paste. During reflow, the molten solder wets the connector leads and plated hole walls, forming solder joints.
This technique is particularly useful for mixed-technology PCB assemblies containing both SMT components and through-hole connectors.
How Does the Pin-in-Paste Soldering Process Work?
The Pin-in-Paste soldering process involves several controlled manufacturing steps to ensure adequate solder volume, component positioning and reliable solder joint formation.
1. PCB Preparation and Design Review
Engineers review the PCB layout, plated-through-hole dimensions, component lead geometry and stencil requirements. Proper hole-to-pin clearance is essential for achieving adequate solder distribution and joint formation.
2. Solder Paste Application
Solder paste is applied to the PCB using a stencil printing process. The stencil apertures are designed to deposit sufficient paste into and around the plated-through holes while minimizing excess solder.
3. Through-Hole Component Insertion
Compatible through-hole components are inserted into the paste-filled holes using manual or automated placement equipment. Accurate insertion helps prevent component misalignment and excessive displacement of solder paste.
4. Reflow Soldering
The PCB passes through a controlled reflow oven. Heat melts the solder paste, allowing it to wet the component leads and plated-through-hole surfaces. The temperature profile must remain compatible with the PCB materials and installed components.
5. Cooling and Inspection
After reflow, the solder cools and solidifies, forming electrical and mechanical connections. The assembled PCB is inspected for solder bridging, insufficient hole fill, component misalignment and other potential defects.
Proper control throughout the Pin-in-Paste process helps manufacturers achieve repeatable soldering results.
How to Calculate Required Pin-in-Paste Solder Volume
Calculating the required solder volume is essential for successful Pin-in-Paste soldering. Insufficient solder may result in incomplete hole fill, while excessive solder can cause bridging or unwanted solder accumulation.
The calculation considers several factors:
- Plated-Through-Hole Diameter: Determines the available space for solder around the component lead.
- Component Lead Dimensions: Influences the volume occupied by the inserted pin.
- PCB Thickness: Determines the length of the plated hole requiring solder.
- Desired Solder Fillets: Additional solder may be required to form acceptable fillets.
- Stencil Aperture Design: Controls the amount of solder paste deposited.
- Solder Paste Metal Content: Determines how much solid solder remains after the paste reflows.
For a simplified cylindrical hole and round component lead, the approximate solder volume needed to fill the space between them can be estimated using:
Required solder volume = π/4 × (Hole Diameter² − Pin Diameter²) × PCB Thickness
This calculation estimates the annular space inside the plated hole. Engineers must also account for external solder fillets, solder paste metal volume and process losses.
Because solder paste contains flux and other nonmetallic materials, the printed paste volume must be greater than the final solid solder volume.
Actual requirements should be validated through stencil design calculations, prototype builds and solder joint inspection.
What Are the Key Benefits of Pin-in-Paste Soldering?
Pin-in-Paste soldering offers several advantages for PCB assemblies containing suitable SMT and through-hole components.
Key Benefit | Description |
Reduced Manufacturing Steps | Combines SMT reflow and through-hole soldering. |
Improved Efficiency | Reduces soldering steps and PCB handling. |
Cost Savings | May reduce labor, equipment and processing costs. |
Consistent Quality | Supports repeatable, reliable solder joints. |
Mixed-Technology Compatibility | Supports suitable SMT and through-hole components. |
Simplified Workflow | May eliminate separate wave or selective soldering. |
These benefits make Pin and Paste soldering an option for manufacturers seeking to streamline mixed-technology PCB assembly.
However, the process is not suitable for every through-hole component. Component temperature ratings, solder volume requirements and PCB design constraints must be evaluated before implementation.
Where Is Pin-in-Paste Soldering Commonly Used?
Pin-in-Paste soldering is used in electronic assemblies where through-hole components must provide mechanical stability while remaining compatible with SMT reflow manufacturing.
Industrial Electronics
Industrial control boards, automation equipment and electronic controllers may use reflow-compatible through-hole connectors to provide dependable electrical connections.
Automotive Electronics
Automotive electronic modules and control systems may incorporate suitable through-hole connectors that can be assembled using the intrusive reflow process.
Telecommunications Equipment
Networking devices, communication modules and telecommunications infrastructure frequently require connectors that support reliable signal and power transmission.
Medical Electronics
Certain medical electronic assemblies can use Pin-in-Paste soldering when component compatibility, manufacturing validation and applicable quality requirements are satisfied.
Computing and Networking Systems
Servers, computing equipment and networking hardware may use through-hole connectors and other compatible components in mixed-technology PCB designs.
Across these applications, the suitability of the process depends on component construction, thermal requirements and solder joint specifications.
Common Challenges in Pin-in-Paste PCB Assembly
Although Pin-in-Paste soldering can simplify manufacturing, several technical challenges must be addressed.
Insufficient Solder Volume: Inadequate paste deposition can cause incomplete hole fill and weak solder joints. Proper stencil aperture design and solder volume calculations help minimize this risk.
Solder Bridging: Excess solder paste may create unwanted connections between adjacent leads. Optimizing stencil openings, component spacing and paste deposition helps prevent bridging.
Component Misalignment: Incorrect insertion can displace solder paste or affect joint formation. Accurate placement and suitable component lead geometry are essential.
Thermal Stress: Not all through-hole components can withstand SMT reflow temperatures. Manufacturers must verify component temperature ratings and establish appropriate thermal profiles.
Inconsistent Hole Fill: Variations in PCB hole dimensions, paste volume and reflow conditions can affect solder penetration. Design reviews and process validation help maintain consistent results.
Addressing these challenges during the design and prototyping stages can reduce manufacturing defects and improve assembly reliability.
How to Choose the Right PCB Assembly Partner for Pin-in-Paste Applications
Selecting an experienced PCB assembly manufacturer is important when evaluating Pin-in-Paste soldering for complex electronic assemblies. The manufacturer should understand SMT assembly, through-hole component installation, reflow soldering, stencil design and solder joint inspection.
OEMs should also consider the manufacturer’s Design for Manufacturability (DFM) support, prototyping capabilities, quality-control procedures and ability to select appropriate soldering methods based on product requirements.
Suntronic Inc. provides comprehensive PCB assembly services, including Surface Mount Technology (SMT), through-hole assembly, selective soldering, quick-turn prototyping and turnkey electronics manufacturing. These capabilities support OEMs developing mixed-technology electronic assemblies with complex manufacturing requirements.
With US-based manufacturing expertise, Suntronic helps customers transition from prototype development to production while emphasizing manufacturing consistency and quality. OEMs considering Pin-in-Paste applications can consult Suntronic’s team to evaluate suitable assembly methods and confirm process availability for their specific designs.
Contact Suntronic for PCB Assembly Solutions
Looking for reliable PCB assembly services? Partner with Suntronic Inc. for SMT and through-hole assembly, selective soldering, quick-turn prototyping and turnkey electronics manufacturing. Contact us today to discuss your PCB assembly requirements.
