Comparing Circuit Board Assembly Methods: When to Use Through-Hole or Surface Mount Components

As electronic product designers seek to maximize functionality while minimizing size, they must carefully choose between through-hole and surface mount component assembly methods. In this in-depth guide, we’ll explore the pros and cons of each approach along with their best use cases. By understanding the key differences, you can select the optimal technique for your unique design goals and manufacturing needs.

Through-Hole Assembly Basics

Through-hole component assembly, also called leaded assembly, involves passing component leads through holes drilled in a printed circuit board (PCB). The leads are then soldered in place on the underside to create electrical connections. This technology has been used for decades and remains common today due to its simplicity and repairability.

Some key attributes of through-hole assembly include:

• Components such as resistors, capacitors, and integrated circuits have axial leads extending from both sides for easy manual or surface mount insertion.
• The physical connection is quite robust since the entire lead engages with the hole wall for mechanical support after soldering.
• Repairs are straightforward since components can be desoldered and replaced individually with basic soldering skills.
• Board designs require dedicated through-holes and sufficient clearance between pads for lead insertion and soldering.

While through-hole assembly has served electronic products well, certain downsides pushed the industry toward newer surface mount techniques.

Surface Mount Technology Emerges

In the 1970s, a new paradigm called surface mount technology (SMT) began gaining traction. Instead of leads passing through board holes, SMT components have short surface-mounted ends or flattened terminations that rest and solder directly onto pad areas.

Continuing advances in SMT over decades drove several improvements:

• Components like resistor networks and chips shrink dramatically in size without axial leads. This enables greater board density and functionality in smaller form factors.
• Automated pick-and-place machinery and reflow soldering ovens make high-volume assembly of tiny components fast and cost-effective.
• Surface-attached joints prove reliable with advances in solder pastes and process controls.
• Conformal coating and other sealing methods ensure durability of exposed joint surfaces.

Today, SMT accounts for the vast majority of high-density circuit boards used in electronics like computers, phones, and more. Its ability to pack many components onto minimal space revolutionized product miniaturization.

Through-Hole Assembly Still Has Its Place

While SMT dominates most commercial electronics manufacturing, through-hole assembly maintains relevance for certain use cases. Some continuing pros of this classic method include:

• Prototyping friendliness – Through-hole is ideal for bringing simple prototypes and one-off PCBs to life quickly using manual assembly.
• Repairability – Locating and desoldering individual through-hole components remains far simpler than SMT. This suits low-volume production and field repairs.
• Higher power capacity – Through-hole’s mechanical interconnect provides better current conduction than surface-mount joints in some power electronics applications.
• Cost effectiveness – For low-complexity PCBs with just a few through-hole parts, the manual assembly costs stay very reasonable.

So through-hole assembly still finds use when factors like prototyping speed, repair-friendliness, power capacity or simple low-cost designs take priority over maximizing density. It competently fills niche roles despite SMT’s dominance.

Comparing Assembly Methods Across Key Metrics

To determine the best assembly approach, consider your design requirements within these important comparison categories:

Component Density

SMT enables far greater packing density through miniaturized parts, automation, and tighter spacing tolerances. Through-hole needs dedicated holes and clearances, limiting footprint optimization.

Manufacturing Scale & Costs

SMT excels at high-volume production due to automated pick-and-place and reflow oven assembly. Through-hole is best for very low volumes due to easy manual assembly. Cost per unit favors SMT significantly above a few thousand units.

Design Complexity

Through-hole designs require dedicated hole placement and clearances that add layout constraints. SMT places fewer layer restrictions and simplifies thermals/mechanicals.

Repairability

Through-hole components can be easily desoldered/repaired by hand. SMT repair requires advanced tools, skills, and often reworks the entire board.

Prototyping Agility

Through-hole enables rapid iterative prototyping through manual building and changes. SMT generally needs design iteration and ordering new prototype boards.

Power Capacity

Through-hole’s larger hole and mechanical fitment provides better current transfer suitable for certain power applications. SMT connections suit most signal/low-power uses well.

Careful evaluation of these categories helps determine the preferable approach for your product’s assembly requirements and goals. Let’s now explore some specific application scenarios.

When to Use Through-Hole Assembly

A number of use cases remain well-suited to through-hole assembly methods:

Prototyping & Low-Volume Production

Through-hole’s manual build simplicity means changing designs and reworking prototypes is a breeze. For short-run production under a few thousand units, per-unit costs also favor through-hole.

Educational & Hobbyist Projects

Learning circuit design and breadboarding through manual through-hole building teaches fundamentals well without heavy equipment needs.

Military, Aviation, Space Electronics

Demand for longevity, reliability and field-repairability under extreme conditions suits through-hole’s robust mechanical connections.

Appliance & Industrial Electronics

Through-hole is exceptional for designs requiring durability against vibration and thermal/mechanical stress over decades of use in harsh environments.

Certain Automotive & Medical Applications

Analogous longevity, reliability and serviceability demands from usages like engine control modules or implantable devices favor through-hole performance.

So in summary, through-hole assembly remains invaluable for applications requiring prototyping agility, cost-efficiency, ease of repair, or enhanced mechanical resilience against stress.

When to Use Surface Mount Assembly

Conversely, SMT yields clear benefits for high-volume consumer electronics and similar applications:

Cell Phones, Computers, Wearables

SMT enables the extreme density that packs today’s powerful systems into ever-shrinking form factors at reasonable per-unit costs.

Hi-Fi Audio/Video Equipment

Consumer demand for smaller smart TVs, sound bars and receivers relies on SMT to densely integrate complex digital features.

Industrial Equipment & Instrumentation

While ruggedness needs favor through-hole, cost pressures driving automation means SMT suits moderate-volume production runs.

Automotive Infotainment & Driver Assist Systems

Vehicles demand versatile interfaces and processing muscle – both best achieved through SMT’s generous component density.

So in summary, when high volumes, miniaturization demands, or complexity drivers require maximum board real estate utilization – SMT delivers unrivaled performance through its ultra-dense packaging capabilities.

Conclusion

Through-hole and surface mount assembly methods both play important roles in electronics depending on unique design and production needs. By understanding each approach’s pros, cons, and best use cases – designers and engineers can confidently select the optimal assembly solution for meeting their goals. With care and insight, the right choice of through-hole or SMT enables bringing products to market successfully.