SMT vs. dip Connector Technical Comparison and Selection Guide

Introduction

In electronic design, the way the connector is installed directly affects the volume, reliability, manufacturing cost and maintenance difficulty of the product.Surface mounting (SMT/SMD) and through-hole insertion (THT/dip) are two of the most popular PCB mounting processes for connectors, each with clear technical boundaries and applicable scenarios.

For precision connector products such as FPC connectors, needle seats, needle row buses, and board-to-board connectors, selecting the wrong installation method will not only affect electrical performance, but may also bury reliability hazards during mass production.This paper systematically compares the differences between SMT and dip connectors from multiple dimensions such as process principle, electrical performance, mechanical reliability, cost structure, and application scenarios, and gives a practical type selection decision framework.

1. Process principle and core difference between SMT and dip

1.1 SMT Surface Mount Technology

The pins or terminals of the SMT (Surface Mount Technology) connector are soldered directly to the pads on the PCB surface without having to pass through the PCB board.The typical process chain is: Solder → paste printing and patching machine mounting → reflow soldering and curing.

Core features of SMT connectors:
– Non-porous design: Terminals do not penetrate the PCB, all solder joints are located at the bottom or side of the connector
– Reflow soldering process: Electrical-Mechanical Connection via Solder Paste Melting – Solidification
– Highly automated: Adapted to high-speed mounting machine, suitable for mass production
– Supports double-sided mounting: PCB can be fabricated on both sides, high space utilization

1.2 dip Through-hole Insertion and Installation Technology

Dip (Dual In-line Package) is a kind of through-hole insertion technology (THT, Through-Hole Technology). Connector pins are inserted into the pre-drilled metallized through-holes of the PCB, and are welded and fixed from the back of the board.The mainstream welding methods are wave soldering or selective wave soldering, and some shaped parts still rely on manual welding.

Core features of the dip connector:
– Through plate anchoring: The pins pass through the PCB and are welded on the back to form a “riveted” mechanical fixation
– Wave soldering/manual welding: The solder is wetted from the back of the PCB through hole to complete the welding
– High mechanical strength: The through-hole structure naturally has stronger tensile and seismic resistance
– One-sided mainly: The components are usually only arranged on the top surface of the PCB, and the through holes will also occupy the inner track space

1.3 Core Differences at a Glance

II. Comparison of electrical performance

2.1 Signal Integrity and High Frequency Performance

SMT connectors have a natural advantage in high-frequency signal transmission.Since the pins are extremely short, the signal loop area is small, the parasitic inductance and parasitic capacitance are far lower than the dip connector, and the signal integrity is better.Taking the board-to-board connector as an example, the coplanarity of the pins of SMT-type products is usually controlled within 0.1mm. With the short pin design, the impedance continuity is better, and it can support higher data transmission rates.

Key Figures: High-speed data connectors (such as PCIe, USB 3.x, Gigabit Ethernet, etc.) are almost completely SMT installed.Some high-end SMT connectors have data rates above 16 Gb/s, while dip connectors are typically only used for low-speed signaling below 1 Gb/s due to their longer pins.

2.2 Current carrying capacity

Current Carrying Capacity is one of the core parameters of connector selection.Overall,Dip connectors generally have better current carrying capacity than SMT connectors of the same specification, for two reasons:

1. Larger pin cross-section: dip connector pins are generally thicker, conductor cross-sectional area is larger, DC resistance is lower
2. Better heat dissipation: The pins pass through the PCB, and the heat can be diffused to the back of the PCB through the through hole, with lower temperature rise

Take common pitch needle products as an example (single contact point, ambient temperature rise of 30 °C):

Selection tips: When multiple needles carry current at the same time, the SMT connector needs an additional derating of 20% ~ 30% due to the heat accumulation effect.When designing high-power products, be sure to refer to the “Multi-pin simultaneous power-on derating curve” in the manufacturer’s specifications.

2.3 Insulation and voltage resistance

In terms of insulation resistance and withstand voltage, the difference between the two is not large, mainly depends on the design of terminal spacing, insulation material and creepage distance.Under the same pitch specification, the insulation performance of SMT and dip connectors is basically equivalent, usually the insulation resistance is ≥ 1000 MΩ, and the withstand voltage can reach AC 500V/1min.

III. Comparison of mechanical reliability

3.1 Mechanical strength and vibration resistance

This is the area where SMT differs the most from dip connectors.

Dip ConnectorThe pins pass through the PCB and form a pad on the back, which is equivalent to a “rivet” structure.This plate-threading anchoring method can withstand significantly higher tensile forces, lateral forces and vibrations.In strong vibration environments such as industrial control, automotive electronics, and rail transit, the mechanical reliability advantages of dip connectors are obvious.

SMT ConnectorRely only on the binding force of the solder to the PCB surface pads for fixing.Solder joints may crack or even fall off when subjected to tensile forces perpendicular to the plate face or a strong lateral impact.For connectors that require frequent plugging (such as external interfaces), pure SMT structures often require additional securing measures (positioning posts, metal clips, dispensing reinforcement, etc.).

3.2 Thermal Cycling and Thermal Stress

Thermal Cycling is an important item for connector reliability testing.In the hot and cold alternating environment, the difference in the coefficient of thermal expansion (CTE) between the connector body and the PCB will generate alternating stress at the solder joint.

SMT connectors are more sensitive to thermal expansion mismatches due to short pins and small solder joints.Especially for large size connectors (such as dual rows of 40Pin or more), prolonged temperature cycling may cause solder joint fatigue cracking.The dip connector has longer pins, which can absorb part of the thermal stress through the elastic deformation of the pins, and the thermal cycle life is usually longer.

Industry Standard Reference: According to the IPC-9701 standard, the thermal cycle life evaluation of surface mount solder joints should consider multiple factors such as pin stiffness, pad size, alloy composition, etc.In general, the proportion of dip connectors passing through -40 ℃ ~ +125 ℃ for 1000 cycles is significantly higher than that of SMT products of the same specification.

IV. Manufacturing process and cost analysis

4.1 Productivity Comparison

SMT connectors are adapted to fully automated production lines, from solder paste printing and mounting to reflow soldering.High-speed mounter can mount tens of thousands of points per hour, and a single SMT line can reach millions of points per day.Dip connectors require plug-in processes (manual or automatic plug-in machines) + wave soldering, with more processes and slower beats.

• SMT: The daily production capacity of a single SMT line is about 5-10 times that of a dip line
• DIP: The plug-in link is highly dependent on labor, and the production capacity is slow to climb.

4.2 Comparison of comprehensive costs

The cost analysis needs to be comprehensively evaluated from the three dimensions of PCB manufacturing cost, component cost, and assembly cost.

Conclusion: In high-volume production scenarios, the comprehensive cost advantages of SMT schemes are significant.However, if the annual production capacity of the product is only thousands to tens of thousands of sets, the upfront investment of the dip program is lower and may be more economical.

4.3 Repair and Maintenance Costs

In terms of difficulty in repair, the dip connector clearly dominates:
– Dip Repair: Ordinary electric soldering iron can be replaced by heating from the back, the maintenance threshold is low, suitable for on-site maintenance
– SMT Repair: Need a hot air gun or repair table, small pitch products also need to be accurately aligned, easy to damage the pads or peripheral components

For industrial equipment, base station equipment and other products that require on-site maintenance, the ease of maintenance of dip connectors is an important plus.

V. Distribution of installation methods of mainstream connector products

For different types of connector products, the market share of SMT and dip varies greatly:

5.1 FPC/FFC connector

FPC Connector (Flexible Printed Circuit Connector) toSMT is mainstream, accounting for more than 90%.This is because:
– The FPC connector itself is positioned for high-density, thin applications
– Common spacing is 0.3mm, 0.5mm, 1.0mm, dip process is difficult to achieve
– Flip Lock and Zif construction naturally fit SMT mount

SMT products of FPC connectors are further subdivided into:
– Horizontal SMT: FPC cable parallel to PCB insertion, minimum height
– Vertical SMT: The FPC cable is inserted perpendicular to the PCB, and the insertion and removal direction is above the board

5.2 Needle Hub/Row Pin Row Female

The Wafer, Pin Header, and Female Header are the most typical categories where the two installation methods coexist.

• Horizontal Sticker (SMT Horizontal): The needle body is parallel to the PCB, which is common in ultra-thin products, such as the 2.0mm PH series horizontal sticker needle holder
• Stickers (SMT Vertical): The needle is mounted perpendicular to the PCB surface, and the height is between the horizontal sticker and the straight insertion
• Bending (SMT Bending): The needle is bent at 90°, taking into account both the height and the direction of plugging and unplugging
• Plug-in (dip portrait): Traditional through-hole insertion, the highest mechanical strength, widely used in industrial control, power supply and other fields
• Bent Insert (dip Bent): 90° corner through hole insertion for side insertion scenes

Selection points: Consumer electronics and smart hardware prioritize SMT needles to save space and cost; industrial equipment, power modules and other scenarios with strong vibration requirements, prioritize dip needles to ensure reliability.

5.3 Board-to-board (B2B) connectors

Almost all board-to-board connectors use SMT.Because B2B connectors usually require high precision (pitch 0.8mm and below) and low profile (stack height a few millimeters), the dip process cannot meet their precision and miniaturization needs.

5.4 High Current/Power Connectors

High-current power supply connectors (such as terminal blocks, high-power pinouts) are mainly dip.Because high-current products require thicker pins and better heat dissipation, through-hole mounting provides stronger mechanical fixation and better heat conduction paths.However, in recent years, through-hole reflow (THR) technology has gradually emerged, taking into account the mechanical strength of the through-hole and the automation efficiency of SMT.

VI. Selection Decision Framework: How to Choose SMT or dip?

For specific projects, it is recommended to evaluate from the following six dimensions:

Dimension 1: Space and Dimension Requirements

• Product pursuit of miniaturization, thinning →Priority SMT
• PCB area is abundant and highly insensitive→, dip cost may be lower

Dimension 2: Current and power levels

• Single needle current ≤ 1A, signal transmission is the main →Priority SMT
• Single needle current ≥ 3A, main power connection →Priority dip(Or choose a special product for high-current SMT and do thermal verification)

Dimension 3: Mechanical environmental conditions

• Consumer electronics, indoor use, low vibration →Priority SMT
• Industrial control, automotive, outdoor use, strong vibration →Priority dip(or SMT + Positioning Column + Dispensing Reinforcement Scheme)

Dimension 4: Production Scale

• Annual production capacity ≥ 100,000 sets →Priority SMT(Automatic cost reduction effect is obvious)
• Annual production capacity < 10,000 sets, manual workshop production can → consider dip (eliminating the input of the placement machine)

Dimension 5: Repair and Maintenance Requirements

• Product maintenance-free, disposable packaging →Priority SMT
• Requires onsite repair, Replaceable → Priority dip

Dimension 6: Cost Target

• Ultimate cost control, high-volume →Lower overall SMT costs
• Low input Fast verification → dip Less upfront investment

VII. Reliability Enhancement Measures in SMT Connector Applications

If the project determines to use SMT connectors, but is concerned about insufficient mechanical strength, reliability can be improved by the following design means:

1. Add Locating Post: Add plastic or metal positioning columns at both ends of the connector and insert them into the corresponding holes on the PCB to share the mechanical stress.This is the most commonly used reinforcement method for SMT needle rows and hubs.

2. Structure with locking clasp is selected: For wire-to-board connectors, select the model with Active Lock to prevent the direct transmission of force to the solder joint when the cable is pulled.

3. Bottom dispensing reinforcement: Increase the bonding area by dotting epoxy or UV glue between the bottom of the connector and the PCB.Note that the amount of glue dispensed should be precisely controlled to avoid contaminating the contact area.

4. Optimize pad design: Strictly follow the manufacturer’s recommended PCB pad size (refer to IPC-7351 standard) to ensure that there are qualified solder fillets in the three directions of toe/heel/side.

5. Reflow Soldering Curve Optimization: Set a reasonable reflow temperature curve according to the plastic material of the connector (temperature resistance grade such as LCP/PA6T/PPS) to avoid coplanarity over-standard caused by plastic deformation.

Conclusion

SMT and dip connectors are not simple “advanced alternatives lagging behind” relationships, but each corresponds to different technical needs and application scenarios.SMT represents the development direction of miniaturization, high density, and automation, and is the mainstream choice for consumer electronics, communication equipment, and intelligent hardware. dip has irreplaceable advantages in terms of mechanical strength, current carrying capacity, and ease of repair, and is still widely used in high-reliability fields such as industrial control, power equipment, and automotive electronics.

For the vast majority of B-side precision connector selection, the core decision logic is:First look at the space and current requirements, then look at the mechanical environment and production scale. The space is tight, the signal is dominant, and the SMT is selected for high-volume production; high current, strong vibration, and the dip is selected for maintenance.If the conditions are between the two, SMT products with positioning columns are often the optimal solution that balances cost and reliability.

Shenzhen Ruixin Shengye Electronic Technology Co., Ltd. focuses on precision connector products such as FPC connectors, needle hubs, needle row mothers, switches, etc., and provides support for the selection of SMT and dip full range of installation methods, covering 0.3mm~5.08mm full pitch specifications.Whether your project is a thin design for consumer electronics or the high reliability requirements of industrial equipment, we can provide matching connector solutions and technical support.