This podcast by Würth Elektronik explains conditions and processes how to mount through-hole components by reflow.
Because of fast assembling and small sizes, designers are turning to surfance mount technology on their PCBs.
Although there are still through-hole (THT) components that need to be soldered by Wave, Through-Hole Reflow (THR), allows designers to solder the Through-Hole Components together with the surfance mount parts in the Reflow Oven, thus canceling the whole Wave Soldering Process; saving time and money.
Enhancing PCB Design with Through-Hole Reflow (THR) Technology
This presentation explores the integration of Through-Hole Reflow (THR) technology in Printed Circuit Board (PCB) design and manufacturing. It highlights the evolution of PCB assembly from traditional through-hole components to modern Surface Mount Technology (SMT), while emphasizing the benefits, process optimizations, and quality considerations associated with THR.
1. Introduction
The evolution of PCB technology has transitioned from large, bulky through-hole components to compact SMT. However, certain components such as connectors necessitate robust mechanical stability, achievable through THR. This paper delves into the rationale, requirements, and processes involved in THR.
2. The Necessity of Through-Hole Components
Despite the prevalence of SMT, through-hole components are essential for:
- High mechanical stress applications
- Connectors requiring strong insertion and withdrawal forces
- High current carrying capabilities
3. Material and Design Requirements
3.1 Housing Material
- Temperature Resistance: Use of Liquid Crystal Polymer (LCP) for high thermal stability up to 260°C.
- Moisture Sensitivity: LCP offers low moisture absorption (MSL1), reducing defects such as voids during reflow.
3.2 Structural Modifications
- Standoffs: Facilitate airflow, solder paste deposition, and visual inspection post-soldering.
- Pin Adjustments: Optimal pin protrusion (0.5 mm) ensures mechanical stability and effective solder joint formation.
4. PCB Layout and Stencil Design
4.1 Via and Pad Design
- Calculation of via volume to ensure adequate solder paste fill.
- Adjustment of pad sizes for optimal thermal and electrical performance.
4.2 Stencil Aperture Design
- Recommendations for stencil thickness (150 µm).
- Aperture shapes (round, rectangular, overprint designs) tailored to component geometry and paste volume requirements.
5. THR Process Stages
5.1 Solder Paste Application
- Manual or automated stencil printing ensuring consistent paste deposition.
5.2 Component Placement
- Use of pick-and-place machines complemented by manual placement for larger components.
5.3 Reflow Soldering
- Reflow profiles aligned with component thermal mass and paste characteristics.
6. Quality Assurance: IPC-A-610 Standards
- Class I: General electronics with minimal reliability requirements.
- Class II: Industrial products with continuous performance expectations.
- Class III: High-reliability applications (e.g., aerospace, medical devices).
6.1 Solder Joint Criteria
- Minimum 75% via fill for Class II and III.
- Visual inspection facilitated by standoffs and AOI systems.
7. Advantages of THR Technology
- Mechanical Robustness: Enhanced stability for connectors and heavy components.
- Process Efficiency: Single reflow process eliminates the need for wave soldering.
- Cost-effectiveness: Reduced production steps lead to lower operational costs.
8. Summary
THR technology bridges the gap between traditional through-hole robustness and SMT efficiency. By adapting component materials, PCB layout, and reflow processes, manufacturers can achieve superior mechanical and electrical performance while optimizing production costs.
