During PCBA processing, fixtures (also known as carriers or jigs, such as DIP wave soldering pallets and SMT reflow carriers) are essential tooling used to assist positioning, support and protection. They are not required for every product, but under certain board types or process scenarios they play an irreplaceable role in safeguarding quality and efficiency — when required but omitted, placement misalignment, soldering defects, board jams and even batch scrapping can easily occur.

So when exactly must fixtures be used? This article explains the two main stages — SMT placement and DIP through-hole insertion — step by step, and provides a quick-reference table to help you decide efficiently.

1. When Fixtures Are Needed in SMT Placement

Throughout the entire SMT process of printing, placement and reflow soldering, the following 6 categories require or recommend the use of carriers.

1.1 Thin boards with insufficient rigidity (thickness 0.2/0.4/0.6/0.8mm and size > 130×130mm)

PCBs with a thickness of 0.2mm, 0.4mm, 0.6mm or 0.8mm and dimensions larger than 130×130mm lack sufficient rigidity, so carriers are required during printing, placement and reflow to keep the board surface flat, ensure full contact with the stencil, and prevent warping or board drop during high-temperature soldering.

1.2 FPC flexible boards

Flexible PCBs have no inherent support and must rely on high-precision carriers for positioning and fixation to complete the full printing, placement and soldering process. Otherwise, they are highly prone to bending and misalignment, resulting in a loss of positional accuracy.

1.3 Odd-form, recessed and board-clamping components

Due to their irregular shapes, uneven center-of-gravity distribution, and structures that extend beyond the PCB outline or are recessed into the board, these components cannot stand on their own after placement and tend to shift during conveyor transport. Fixtures are required for auxiliary positioning and support to ensure positional stability and soldering quality throughout printing, placement and reflow.

1.4 PCB size smaller than 7×7cm

When the PCB size is smaller than 7×7cm, it falls below the minimum acceptable size for SMT placement machine rail transport. The machine cannot effectively clamp and position the board, making printing, placement and reflow difficult to perform normally. Fixtures are needed to enlarge the clamping area.

1.5 High-precision double-sided boards

If both sides contain heavy components or high-density areas, bottom-side solder joints may soften at high temperature during the second reflow, causing components to fall off. Carriers can effectively support and protect the already-soldered side, ensuring the quality of the double-sided process.

1.6 Design deficiencies (no tooling edge, excessive aspect ratio, insufficient rigidity)

- No tooling edge: The machine cannot effectively clamp and position the PCB, preventing normal transport through printing, placement and reflow.

- Aspect ratio greater than 1:1.5: With the long side and short side differing excessively, the board tends to wobble, misalign, or even jam and scrap during rail transport.

- Insufficient board rigidity: When the PCB size exceeds what its rigidity can withstand, the board tends to warp under high temperature, affecting placement accuracy and soldering quality.

2. When Fixtures Are Needed in DIP Insertion

2.1 FPC flexible boards

Flexible PCBs have no inherent support and must rely on dedicated fixtures for positioning and fixation to keep the board surface flat during wave soldering transport, avoiding poor lead soldering or component misalignment caused by board warping.

2.2 Odd-form, recessed and board-clamping components

Due to their irregular shapes, uneven center-of-gravity distribution, and structures that extend beyond the PCB outline or are recessed into the board, these components cannot stand on their own after insertion and tend to wobble, shift or even drop during rail transport. Customized fixtures are required for auxiliary support and position limiting to ensure accurate positioning and reliable soldering during wave soldering.

2.3 Masking and protection of the through-hole soldering side

If the through-hole soldering side contains already-placed SMT components or pads requiring protection, an oven pallet must be used to physically mask them, preventing the solder wave from causing shorts, solder bridging, solder ball residue and other quality issues.

2.4 PCB size smaller than 7×7cm

When the PCB size is smaller than 7×7cm, it falls below the minimum acceptable size for wave soldering machine rail transport. The machine cannot effectively clamp the board edge, which may lead to unstable transport, board jams or uneven soldering, making it difficult to complete wave soldering normally.

3. Quick-Reference Table: Does Your Board Need a Fixture?

4. FAQ About Fixtures

Q1: What is the difference between a fixture, a carrier and a jig?

They are essentially common names for the same type of tooling — all referring to tooling used for auxiliary positioning, support and protection in PCBA processing. By convention, "carrier" is more commonly used for load-bearing support in SMT reflow soldering, while "fixture/jig" is a broader term covering various positioning, clamping and masking tooling (e.g., wave soldering pallets). The exact usage should follow the production line's process documents.

Q2: Do thin boards always need a carrier?

Generally, yes. Thin boards with a thickness of ≤0.8mm and relatively large dimensions require carrier support to prevent deformation during printing, placement and reflow. Whether it is strictly mandatory depends on a comprehensive evaluation of board thickness, dimensions and component layout — we recommend confirming with Juehui Weiye Circuits' PCBA engineering team.

Q3: Does using fixtures increase cost?

Yes, but only to a limited extent. Fixtures are a one-time tooling investment that can be amortized across batch production. Compared with the placement misalignment, soldering defects and board jam/scrap caused by not using fixtures, fixture cost is usually far lower than the quality loss — and the larger the batch, the lower the unit cost.

Q4: What information is needed for custom oven pallets?

Generally: Gerber/PCB outline files, board thickness, component layout drawings, process requirements (reflow/wave), panel size, etc. The factory's engineering team designs the positioning and support scheme based on these.

5. Conclusion

Though small, fixtures are a key guarantee of PCBA yield. Deciding "whether to use a fixture" essentially means deciding "whether the board can maintain flatness and stability on its own during line transport and high-temperature soldering." For any scenario involving thin boards, FPC flexible boards, odd-form components, small sizes, double-sided heavy loads or no tooling edge, we recommend communicating with the PCBA engineering team in advance to customize a carrier/fixture solution.

(https://www.szjhpcba.com/) — One-stop PCBA processing service provider specializing in PCBA prototypes and small-to-medium-batch turnkey (kit + material) customization, covering SMT placement, DIP through-hole insertion, and special-process PCBs such as high-multilayer, HDI, heavy copper and rigid-flex boards, with high-precision single/double-sided placement of 01005, 0201, BGA and QFN components and post-soldering of through-hole parts. Our engineering team can help evaluate fixture requirements and provide custom oven pallet solutions. Welcome to contact us.