2.4 Board Handling & Line Control

The unseenflow infrastructureof panels between printerSMT andstations oven—— handled by conveyors, buffers, and communication links—oftenlinks determines— whetheris acritical linefor runsachieving smoothlystable orthroughput. constantlyLine stutters.control Reliableensures boardthat handlingboards keepsare panelspresented centered,correctly clamped, and moving without intervention, while buffers absorb small interruptions soto the slowestmachinery, stationflattened dictatesfor pace without starving the rest. Handshake protocols evolve this flow: SMEMA ensures basic transfers, but Hermes adds intelligence by passing board identity, size, and recipe downstream, cutting setup time and tightening traceability. Even warped panels can be tamed with supports, mapping, and guardrails, keeping paste,precision placement, and reflowmoved aligned.efficiently without causing jams or starvation. The shift from blind communication (SMEMA) to intelligent networking (IPC-Hermes) provides the foundation for full line synchronization, automated changeovers, and complete product traceability.

2.4.1 Conveyors &and widthPhysical controlConstraints

(

Conveyors form the quietphysical backbone)backbone of the line. Their consistent operation is necessary for stable machine alignment.

• Edge-Width Control and Centering: Automated edge-belt conveyors with auto auto-width keepadjustment are essential. They ensure boards are always centered and gasketspresented tightto the printer's tooling plate or mounter's clamp mechanism at a known, consistent position.
• Warp Mitigation (The Flatness Problem): Boards must be held flat at the printer;point teachof threeprocess. fiducialsStop gates with integrated lift pins or vacuum blocks are non-negotiable at the printer (for paste flatness) and let the lanepick-and-place handmachine you(for aplacement board that’s already aligned.accuracy).
• Stop gate + lift pins/vac toolingStandardization: at printers and mounters flatten the PCB where paste goes and where parts land. Your panelHouse railsRule: from design (2.5) give belts something sturdy to hold.
• NG (No-Good) diverters route failed panels to a side buffer soStandardize the main lane never stalls.

House rule: pick one conveyor family peracross linethe forentire SMT line. This ensures identical board stops, clampsclamping force, and width recipes— between machines, making product changeovers becomerepeatable buttonand presses,rapid.

NG notDiverters: wrenchDedicated time.

NG (No-Good) diverters must be installed (typically after SPI and AOI) to automatically route defective panels to a side buffer without halting the main production flow.

2.4.2 Handshakes:Handshake SMEMAProtocols: vsBlind IPC-HermesTransfer vs. Smart Genealogy

The communication protocol dictates the level of line automation and data integrity.

Protocol	Function	Data Transfer (oldThe switch"Handshake")	Managerial/Traceability vs smart chat)Value
SMEMA (classic):IPC-SMEMA-10)	Classic/Baseline. simpleSimple “boardelectrical availablesignals.	Blind. /Sends machineonly ready”"Board Available" or "Machine Ready" via dry contacts. Rock-solid, but contact.	blindZero.—no Requires manual barcode scanning at each station to break board identity or recipe hints.identity.
IPC-Hermes-9852 (modern):	Modern/Smart. upstreamTCP/IP sendsbased.	Intelligent. Passes boardBoard ID, size, barcode/ID,product type, and workrecipe stepname sodownstream.	High. downstreamEnables canrecipe pre-loading, automated width changes, and unbroken board genealogy.

pre-loadAction: If the recipeequipment andsupports width, and attach scans to genealogy without extra readers. This is how your board-to-box story stays unbroken while lines change products.

If you can turn onit, Hermes, domust it.be Keepenabled. SMEMAIt ascuts adown safetychangeover nettime but(OpEx) letby Hermespre-loading carry identityparameters and width.is Yourthe buffersfoundation andfor NGfull gatestraceability getwithout smarterrelying overnight.on repetitive barcode scans.

2.4.3 Buffers thatand smoothLine the beatSynchronization

• Inline

  Buffers accumulatorsare beforedeliberately thesized constraintinventory (slowestzones machine)that absorb micro-stops upstream;and adecouple smallline onespeed variations, protecting the overall Takt.

  • Constraint Buffering: The most critical buffer must be placed immediately before the constraint (the slowest machine/bottleneck). This ensures the bottleneck is never starved due to micro-stops upstream.
  • Decoupling: A smaller buffer placed after itthe constraint protects the restdownstream reflow oven from micro-stops at the bottleneck, maintaining a consistent thermal profile pace.
  • Sizing Principle: Buffer slots should be sized based on the longest average micro-stop time of the line.
  • Loader/Unloaderslowest +machine Magazinedivided buffer bookendby the line forTakt, kit changes and WIP control.
  • Flip/Bypass modules: put them where double-sided flows want a clean “go around” path.

  Sizing tip: estimate buffer slots = (largest single-machine micro-stop seconds ÷ line TAKT) ×plus a safety factor.margin. IfShort youboards don’tor knowcomplex yourchangeovers micro-stopsoften yet,require startlarger with 5–10 slots and adjust.buffers.

2.4.4 WarpWarp, &Flatness, flatnessand compensationProcess (make boards look flat)Guardrails

Warped boards fakeare outa pasteprimary source of printing and placement.placement Fighterror. it in three layers:

A) Upstream prevention

• Specify panel rails, tooling holes,Prevention and balancedcontrol stacksare essential.
  1. Incoming Material Spec: Boards must meet a strict flatness tolerance at incoming quality control (Ch.IQC), 2.5)typically so≤ fabrication0.75% and handling cause less bow.

B) Atof the station

panel

• Printer:diagonal. mapPanels boardexceeding supportthis withlimit pins/vacshould blocksbe right under big paste fields; if SPI shows regional lows, add pins before touching squeegee settings.quarantined.
• PnP:Station Compensation: enableMachines boardmust utilize height mapping and dense support to physically constrain the board. Reflow ovens (ifhandling available)long or use dense supports; keep clamp force even so the head isn’t “chasing” Z.
• Reflow: long, thin panels mayshould needuse edge rails and center support fingers onto prevent sag that causes solder movement (opens) during the conveyorpeak tothermal stop sag through heat.zone.

Line-Stop

C)Logic: ProcessDefine guardrails

clear

• Setcriteria afor flatnessSoft specStops at incoming (e.g., ≤0.75% of diagonal) and a rework path for outliers; don’t tune the whole line around one potato-chip panel.

2.4.5 Line-stop logic & NG flow (decide once, wire it everywhere)

• Stop types: define soft stop (finish current board, hold handshakes) vs hard stop (halt upstream) and when each is used (jam, missing width change, recipe mismatch).
• NG logic: AOI/SPI/Test flags push the panel ID via Hermes to NG buffers automatically; operators don’t chase paper tags. (This ties back to Chapter 4’s scanning.)

2.4.6 What planners & leads watch

• Starvation / Blocked minutes at each machine (should fall after you add the right buffers).
• Width-change time and recipeHard sync errorsStops (Hermesemergency shouldhalt). makeNG theselogic nearlymust vanish).
• Boardbe flatness rejects at printer clamp-down (trend vs lot/vendor—feed backwired to fabthe withmain yourcommunication 2.5system rules).

so

2.4.7that PocketSPI checklistsor (postAOI atalarms automatically trigger the lineNG PC)diverter, preventing further processing of a faulty unit.

Final Checklist: Operational Flow

Conveyors & buffersArea	Uptime Goal	Managerial Focus
Conveyor	Auto-width recipes savedverified; per product; clamps/stops verified Buffer before constraint; NG diverter tested; bypass path OK Handshakes SMEMA I/O healthy; Hermes IDs seen end-to-end (printer → mounters → AOI/test) Flatness Supportsupport pins/vac blocks placed under pasteall BGA/fine-pitch areas.	Reduce time spent on manual width changes.
Handshake	Hermes enabled and BGA/QFNverified zonesend-to-end (printer to AOI/Test).	Eliminate recipe mismatch errors and auto-log genealogy.
Buffers	Buffer placed before the Constraint; Starvation/Blocked Minutes dashboard metric trend is zero.	Protect Takt Time and maximize OEE.
Flatness	Incoming inspection active; warpWarp screenScreen active;confirms outliersadequate quarantinedsupport orbefore re-fixturedprocess start.	Prevent yield loss due to random panel distortion.

By standardizing conveyors, automating width and recipe handshakes, and buffering constraints, lines stay synchronized and resilient. The outcome is steady takt, consistent quality, and a production rhythm that holds true across shifts.