Mixed SMT and DIP Assembly: The Practical Guide to Combined Through-Hole and Surface Mount Manufacturing

Modern electronic products rarely rely on a single assembly technology. A typical industrial controller, medical device, or automotive module might pack hundreds of tiny surface-mount resistors and ICs alongside bulky connectors, relays, electrolytic capacitors, and transformers that simply cannot exist in surface-mount form. Bridging these two worlds on one circuit board is the job of mixed assembly — and getting it right demands a manufacturer that controls both processes under one roof.

This guide walks through what mixed SMT and DIP assembly means, when it makes sense, how the combined process flows, and what to look for when choosing a dip plug-in and smt mixed assembly service partner.

Two Technologies, One Board

Surface Mount Technology (SMT) places components directly onto pads on the PCB surface and bonds them through reflow soldering. It enables high component density, supports tiny packages down to 01005 chip sizes and fine-pitch BGAs, and runs at high throughput on automated pick-and-place lines. SMT is the backbone of nearly every high-volume electronics product.

Through-hole technology — often called DIP (Dual In-line Package) plug-in assembly — inserts component leads into plated holes in the board and secures them with wave soldering or hand soldering. Through-hole joints are mechanically stronger than surface-mount joints because the solder fills the plated barrel and wraps around the lead. That strength matters for parts that endure mechanical stress, carry high current, or need to survive repeated mating cycles.

When Mixed Assembly Is the Right Choice

Not every product needs both technologies. Mixed assembly is the natural fit when a board contains:

• High-pin-count ICs, fine-pitch QFNs, or BGAs that only come in surface-mount packages
• Large electrolytic capacitors, transformers, or inductors that require through-hole mounting for thermal and mechanical stability
• Board-to-board connectors, terminal blocks, or headers that experience insertion and extraction forces
• Power semiconductors or relays that generate heat and benefit from the thermal mass of plated through-holes
• Components specified by the end customer that are only available in through-hole form

In these cases, a board that combines smt pcb assembly with through-hole soldering delivers the best of both worlds: compact, automated placement for the majority of components, and rugged mechanical joints for the parts that need them.

How the Mixed Assembly Process Works

A mixed-technology board is not assembled in a single step. The process is sequenced so that each technology does not interfere with the other. A typical flow runs as follows:

• Solder paste printing — A stainless-steel stencil applies solder paste only to the surface-mount pads. Through-hole locations are left dry at this stage.
• SMT pick-and-place — Automated placement machines position surface-mount components onto the pasted pads at high speed and with high precision.
• Reflow soldering — The board passes through a multi-zone reflow oven that melts the paste and forms the surface-mount joints.
• Through-hole insertion — Operators or automated insertion equipment place DIP and axial/radial components into their plated holes, often on the opposite side of the board or in areas masked off from SMT.
• Wave soldering or selective soldering — A reliable wave soldering service passes the board over a molten solder wave, filling the through-hole barrels and wetting the leads. Selective soldering may be used when SMT components on the bottom side must be protected from the wave.
• Lead cutting and repair welding — Excess leads are trimmed, and any touch-up soldering is performed at rear-welding stations.
• Board washing and inspection — The board is cleaned and then inspected through AOI, visual checks, and X-ray where needed.
• Functional testing — ICT, FCT, and other electrical tests verify that both the SMT and through-hole sections perform to specification.

The sequence matters. Soldering surface-mount parts first through reflow, then soldering through-hole parts through wave soldering, prevents the wave from dislodging or reflowing SMT joints. For boards with SMT components on both sides and through-hole parts as well, adhesive may be used to hold bottom-side SMT parts in place during wave soldering.

SMT vs. Through-Hole at a Glance

Quality Standards and Inspection in Mixed Assembly

Mixed-technology boards are inspected against the same family of IPC standards that govern single-technology boards, but the inspection covers two joint geometries. IPC-A-610 defines acceptability criteria for both surface-mount solder joints and through-hole solder fill, including the percentage of barrel fill required for plated through-holes. A manufacturer that works to these standards can give buyers confidence that both sides of the board meet the same quality bar.

Inspection tools for mixed assembly typically include SPI for solder-paste volume, AOI for component placement and surface-joint quality, X-ray for hidden joints under BGAs and QFNs, visual inspection for through-hole solder fill and lead protrusion, and functional testing for electrical performance. The combination of optical, X-ray, and electrical verification is what catches defects that any single method would miss.

What to Look for in a Mixed Assembly Partner

Selecting a manufacturer for a mixed-technology board goes beyond checking whether they own both SMT and wave-soldering equipment. The practical questions to ask include:

• Does the factory run dedicated SMT and DIP lines, or does one line try to do everything? Dedicated lines reduce setup errors and improve consistency.
• What placement precision can they achieve? Boards with 01005 components or 0.2 mm BGA pitch need high-precision pick-and-place equipment.
• Do they offer a through-hole soldering service that includes both wave soldering for volume and selective or hand soldering for low-quantity or rework needs?
• What inspection and testing do they perform in-house? AOI, X-ray, ICT, and FCT should all be available without outsourcing.
• Are they certified to the management-system standards relevant to your industry — ISO 9001 for general quality, IATF 16949 for automotive, ISO 13485 for medical?
• Can they handle the full chain from PCB fabrication and component sourcing through oem pcba manufacturing, conformal coating, testing, and finished-product assembly? A one-stop partner reduces handoff risk.

Farway Electronic: Mixed Assembly Under One Roof

Farway Electronic, based in LongGang, Shenzhen, operates a 2,000-square-metre production facility built around both SMT and through-hole capability. The factory runs two SMT lines equipped with Yamaha medium- and high-speed placement machines and a Jintuo ten-zone reflow oven, alongside two DIP plug-in lines with Nitto wave-soldering equipment and 24 rear-welding stations for repair and touch-up.

This dual-line setup lets Farway handle mixed-technology boards without sending any portion of the work to a subcontractor. SMT placement covers components down to 01005 package size and BGAs with 0.2 mm pitch, while through-hole processing runs from component forming and insertion through wave soldering, lead cutting, board washing, and functional testing.

Quality is anchored by IPC-oriented inspection — SPI, AOI, FAI, X-ray, ICT, FCT, thermal imaging, and high/low-temperature reliability testing are all performed in-house. The company holds ISO 9001, ISO 13485, IATF 16949, and ISO 14001 certifications, making it a fit for automotive, medical, industrial, and new-energy projects where audit-ready process control is mandatory.

Conclusion

Mixed SMT and DIP assembly is not a compromise between two inferior options. It is a deliberate design and manufacturing strategy that pairs the density and speed of surface mount with the mechanical strength and power-handling capability of through-hole soldering. For products that contain both fine-pitch ICs and rugged connectors, choosing a manufacturer with proven dual-line capability is the most direct path to a reliable, production-ready board.

If your next project needs a combined surface-mount and through-hole build — with component sourcing, testing, and coating handled by a single partner — Farway Electronic's Shenzhen facility is equipped and certified to take it from prototype to volume production.