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2.7 Machine Architectures

Machine architecture defines the DNA of the Surface Mount Technology (SMT) line, establishing a fixed trade-off between raw speed (CPH), component flexibility, and capital investment (CapEx). The choice dictates how the placement process manages the physics of movement, which impacts two major production variables: Takt Time and Changeover Efficiency.

2.1.7.1 The Two Core Architectures: Gantry vs. Turret

Placement machinery is categorized by its primary motion system, which determines its optimal product mix.

Feature

Modular/Gantry Systems (Flexible Mounters)

Rotary/Turret Systems (Chipshooters)

Motion System

X-Y gantry, moving over a stationary board.

Rotary head spins components past stationary vision.

Placement Speed (CPH)

Moderate to High. (Up to 80k CPH per module)

Extremely High. (Often ≥ 100k CPH) in pure chip mode)

Component Range

Excellent. Handles everything from 01005 to large, odd-form, heavy connectors, QFPs, and BGAs.

Limited. Best for small passives (01005 – 0603). Struggles with heavy/large ICs.

Placement Accuracy

Superior. Uses linear encoders and dedicated Z-axis control. Essential for ≤ 0.4 mm pitch.

Good but generally lower for large components due to high speed/inertia.

Changeover Time

Fast. Component swap is typically managed via smart feeders/cart changes.

Slow. Fixed feeder banks mean high cost/time for swapping parts not in the bank.

CapEx/Flexibility

High CapEx initially, but excellent scalability (add modules/gantries) and flexibility (high-mix capability).

Lower CapEx per placement, but fixed capability and poor high-mix performance.

Strategic Note: For High-Mix/Low-Volume (HMLV) production with frequent changeovers, the Flexible Modular/Gantry system's efficiency outweighs its higher CapEx. For High-Volume/Low-Mix stability, the Turret system delivers the best cost per placement for passives.

2.1.7.2 Line Topologies: Structuring the Flow

The arrangement of PnP machines must match the product's component distribution and the required Takt Time.

1. Role Split (Chipshooter – Flexible)

  • Setup: Chipshooter (PnP1) handles all high-volume passives, then the board moves to the Flexible Mounter (PnP2) for large/complex ICs.
  • When it Wins: Boards dominated by thousands of small chips and relatively few large parts. This maximizes speed by pushing the fast work to the fastest machine.
  • Watch-Out: If the flexible mounter becomes the bottleneck (Constraint), the chipshooter sits idle waiting. Requires disciplined load balancing (see below).

2. Tandem Split (Flexible A – Flexible B)

  • Setup: Two flexible mounters of similar capability run in series, splitting the component count roughly 50/50
  • When it Wins: The most common setup for HMLV. It simplifies feeder management (as parts can run on either machine), speeds up changeovers, and offers redundancy.
  • Watch-Out: Requires symmetrical programming and near-perfect load balancing to avoid bottlenecking.

3. Dual-Lane / Parallel Processing

  • Setup: The entire line (Printer, PnPs, Reflow) processes two PCBs simultaneously on two separate conveyor tracks, or the PnP machine internally handles two boards at once.
  • When it Wins: Extremely short boards or highly aggressive Takt Time requirements where placement time is the constraint. Ideal for "pack-and-stack" products.
  • Watch-Out: Requires twice the number of feeders or mirrored feeder setups for both lanes, significantly increasing kitting complexity and OpEx.

2.1.7.3 Load Balancing and Throughput Management

The line Takt Time is always defined by the slowest process step—the Bottleneck. In a PnP line, this is the machine with the highest placement time.

  1. Measure Cycle Time: The calculation of the placement time per board for each machine (excluding board travel time) must be the primary metric for balancing.
  2. Target Symmetry: Cycle times of all PnP machines in the line should be within ±10% of each other.
  3. Work Allocation: If PnP2 is slower than PnP1, lower-complexity, higher-count components (e.g., resistors, common capacitors) must be re-allocated from the slow machine back to the faster one until cycle times equalize.
  4. Uptime Strategy: To maximize throughput, permanent feeder banks must be established for high-runner common components. This significantly reduces the time and risk of kitting and changeovers, cutting down OpEx.

Uptime Rule: Maximize Permanent Feeder Banks. By keeping 80% of your common components (like 0402 passives) in fixed slots, you massively reduce the time and risk involved in every single changeover, cutting down on OpEx and kitting errors.

2.1.7.4 Feeder Management and Traceability

Feeder capacity and changeover efficiency are critical operational drivers of the PnP process.

  • Feeder Density: Machine choice impacts the total feeder capacity per footprint, which directly limits the maximum component complexity (unique part numbers) a board can have.
  • Smart Feeders: The use of Intelligent Feeders is essential. These feeders communicate their Part ID and position to the machine's software, eliminating the primary risk of mis-kitting (placing the wrong part number).
  • Kitting Carts: Changeover time is minimized by using dedicated kitting carts or exchange trolleys, allowing the feeders for the next job to be prepared offline while the current job is running.



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