Surface Mount PCB Assembly , High Density HDI Class 3 SMT Circuit Board Assembly

Surface Mount Technology (SMT) is the backbone of modern electronics manufacturing. However, as components shrink and densities increase, the margin for error disappears. DuxPCB delivers industry-leading SMT assembly services, bridging the gap between high-speed throughput and micron-level precision.

We do not simply place components; we manage the entire thermal and chemical process of soldering. From 3D Solder Paste Inspection (SPI) to Nitrogen (N2) Reflow, our facility is optimized to handle the most complex footprints, including 01005 passives, 0.2mm pitch uBGAs, and POP (Package-on-Package) stacks. Whether you need a quick-turn prototype or high-volume mass production, DuxPCB ensures every solder joint meets IPC-A-610 Class 3 reliability standards.

Speed is a commodity; Yield is the currency. We achieve near-zero defect rates through rigorous process control variables that generalist assemblers often ignore.

70% of SMT defects originate at the printing stage. We treat solder paste as a critical chemical reagent.

• Storage & Handling: Automatic "First-In-First-Out" (FIFO) refrigerated storage and automated softening/mixing to ensure optimal viscosity.

• Nano-Coated Stencils: We utilize laser-cut, electro-polished stencils with nano-coatings to ensure smooth paste release for fine-pitch apertures, preventing bridging.

We don't guess; we measure. Before a single component is placed, our inline 3D SPI machines scan the printed PCB.

• Volumetric Analysis: We measure not just the area, but the volume and height of the solder paste deposit.

• Defect Prevention: Any board with insufficient paste or offset printing is rejected immediately, preventing "dry joints" or "tombstoning" later in the process.

Oxidation is the enemy of a good solder joint. DuxPCB utilizes Nitrogen-purged reflow ovens.

• Better Wetting: N2 reduces the surface tension of the molten solder, allowing it to spread more evenly over the pad.

• Void Reduction: By preventing oxidation during the liquidous phase, we significantly reduce voiding in BGA and QFN thermal pads.

Our equipment allows us to handle the full spectrum of modern electronic components.

We break down the assembly into controlled stages to ensure repeatability.

Phase 1: Solder Paste Printing
The PCB is loaded into the automatic printer. The vision system aligns the stencil fiducials with the PCB. A squeegee forces Type 4 or Type 5 (for fine pitch) solder paste through the apertures.

Phase 2: 3D SPI Verification
The SPI machine inspects the paste deposits. If the volume deviation exceeds +/- 15%, the board is automatically cleaned and reprinted. This eliminates the root cause of bridging and open circuits.

Phase 3: High-Speed & Precision Placement

• Turret Heads: Place passive components (R/C) at high speeds (up to 100,000 CPH).

• Precision Heads: Use vacuum nozzles and vision alignment to place large ICs, BGAs, and connectors with slow, controlled descent to avoid splashing the wet paste.

Phase 4: Reflow Soldering
The board passes through a multi-zone reflow oven (typically 8-10 zones).

• Preheat/Soak: Activates the flux and removes volatiles.

• Reflow: Solder reaches liquidous temperature (approx. 245°C for SAC305).

• Cooling: Rapid controlled cooling to form a fine-grain crystalline structure for strong joints.

Phase 5: Automated Optical Inspection (AOI)
Cameras scan the finished board, checking for:

• Component presence/absence

• Polarity (rotation)

• Solder fillet quality

• Tombstoning (lifted parts)

Challenge: The "Tombstone" Effect
Issue: Small passive components (0402/0201) stand up on one end during reflow due to uneven wetting forces.

• DuxPCB Solution: We analyze the thermal balance of the pad design during the DFM phase. In production, we strictly control the oxygen level (via Nitrogen) and the preheat profile to ensure both pads wet simultaneously.

Challenge: QFN/BTC Voiding
Issue: Large thermal pads under QFNs trap gas, creating voids that hinder heat dissipation.

• DuxPCB Solution: We use a "Window Pane" stencil design to break up the large paste deposit into smaller squares, providing channels for outgassing. We also optimize the reflow soak time to allow volatiles to escape before the solder melts.

Challenge: Warpage on Flexible Boards
Issue: Flex PCBs (FPC) are flimsy and warp during printing/placement.

• DuxPCB Solution: We design and fabricate custom Magnetic Carriers (Pallets). The FPC is taped or magnetically held flat on the carrier, ensuring it behaves like a rigid board throughout the SMT process.

• IPC-A-610 Class 2: Standard for consumer/industrial electronics.

• IPC-A-610 Class 3: High-reliability standard for automotive, medical, and aerospace (available upon request).

• ESD Control: ANSI/ESD S20.20 compliant facility. All flooring, workstations, and operators are grounded.

• First Article Inspection (FAI): For every new batch, the first board is fully inspected (component values measured via LCR meter) before the full run begins.

Q: Can you assemble SMT components on Flexible PCBs (FPC)?
A: Yes. We use magnetic pallets to support the flex circuit, ensuring the surface is perfectly flat for paste printing and component placement. We can handle components down to 0201 size on FPC.

Q: Do you support Double-Sided SMT assembly?
A: Yes. For double-sided boards, we typically mount the side with lighter components first. On the second pass, the surface tension of the molten solder holds the bottom-side components in place. For heavy bottom-side parts, we may use glue dispensing.

Q: Can you work with Cut Tape components for prototypes?
A: Absolutely. While Tape & Reel is preferred for automation, we have specialized "Cut Tape Feeders" and JEDEC tray carriers to handle loose strips of components for low-volume prototype runs without charging setup fees.

Q: How do you handle "No-Clean" flux vs. "Water-Soluble" flux?
A: We standardize on No-Clean flux for reliability and cost. However, if your application requires it (e.g., high-voltage boards), we can use Water-Soluble flux and perform an inline aqueous wash to remove all residues.

SMT is not just about putting parts on a board; it is about statistical process control. Choose a partner who measures quality in microns.

Send your Gerber and BOM to DuxPCB. Our engineers will perform a DFM review to check for footprint mismatches and optimize your design for high-yield manufacturing.