Learning objectives
- Load panels onto the line with correct orientation, support and handling
- Judge board flatness and recognise warpage that will cause print and placement errors
- Keep solderable surfaces clean and free of fingerprints and contamination
- Set support pins or fixtures correctly for thin and double sided panels
Lesson
The line can only build as well as the board it receives at the loader. At this stage panels are taken from their packaging and loaded onto the conveyor or magazine loader with the correct orientation, travelling on their edge rails so the solderable surfaces are never dragged, stacked or touched. Handling discipline is the first lesson. Bare hands stay off the pads and lands, because skin oils deposited on a solderable surface will show up stages later as dewetting, where solder refuses to spread and grip. Boards are held by their edges, and panels that have waited in storage are checked before they run.
Preparation is the second lesson. Dust and fibres are removed with a board cleaner, typically a tacky roller or air cleaning unit, because a fibre under a stencil becomes a print defect. Panels are also looked over for transit damage at this point: scratched solder mask, chipped edges and dented corners are all reasons to hold a panel for assessment rather than load it and let later stages discover the damage at full price. The conveyor itself is set for the panel: edge clearance checked, rails parallel, and the transfer from loader to printer smooth, because a panel that drops or shudders on its way in arrives with its surface condition and its alignment already compromised. Some lines bake boards before printing to drive off absorbed moisture, applying the same moisture respect taught in Stage 1. Flatness is judged at this point. A warped panel will not gasket against the stencil, will sit at slightly different heights under the placement nozzles, and will carry those errors through every later stage. Support is the third lesson. Thin panels and double sided panels flex under print pressure and placement force, so support pins or dedicated fixtures are set under the print and placement areas. An unsupported board that flexes today can crack ceramic capacitors that only fail months later in the field.
James Onsomu writes in his lean PCB manufacturing book about standard operating procedures and visual management keeping every run consistent. Loading is where that standard work begins. The correct orientation, the support pattern and the handling rules are written, visible and followed the same way on every shift, so the printer receives a clean, flat, supported panel every single time.
Key numbers
- Board orientation: verified against the job documentation for 100 percent of panels at load
- Support: pins or fixture placed under the full print and placement area, with no unsupported span left to flex
- Handling: contact with solderable surfaces by bare hands, zero times
- Flatness rule: a panel that does not sit flat on its rails is held for assessment, never forced through
Defects to spot
- Warped panel: poor storage or absorbed moisture, seen as a bow when the panel sits on its rails
- Fingerprints on pads: bare hand handling at load, later seen as dewetting at the solder joint
- Flex damage started: support pins missing under a thin panel
- Reversed panel: orientation not checked against the job documentation
Stage check, self test
Answer each question, then open the answer to check yourself. Passing standard: 80 percent, at least 4 of 5 correct.
1. Why must bare hands stay off the pads and lands?
A. Skin oils on solderable surfaces lead to dewetting at soldering
B. Fingerprints make the board heavier
C. The pads are sharp
D. It slows the conveyor down
Show answer
Answer: A
2. What does a warped panel cause downstream?
A. Better paste release
B. Faster placement
C. Stronger solder joints
D. Print and placement errors, because alignment and height vary across the panel
Show answer
Answer: D
3. What is the purpose of support pins under a thin panel?
A. To mark the panel as inspected
B. To stop the board flexing under print pressure and placement force
C. To hold spare components
D. To cool the board after reflow
Show answer
Answer: B
4. An operator finds a panel with a visible bow at the loader. What is correct practice?
A. Run it anyway, the oven heat will flatten it
B. Bend it flat by hand and load it
C. Hold it for assessment rather than forcing it through the line
D. Place it at the bottom of the stack
Show answer
Answer: C
5. Why are boards sometimes baked before printing?
A. To drive off absorbed moisture
B. To soften the solder mask
C. To warm them for the operators
D. To test the oven
Show answer
Answer: A
Previous: Stage 1: Incoming inspection, storage, ESD and moisture control