Board Handling Between Lines

A board travels further than most people realise between the start and the end of a production line, and every transfer is an opportunity for damage. Handling defects are rarely dramatic: a chipped component, a hairline crack in a solder joint, an edge that has been scuffed or a connector that no longer mates cleanly. They are also hard to attribute, because the damage may occur several operations before it is detected.

<img src="https://www.gopcba.com/wp-content/uploads/2024/09/Board-Cutting2-1.png" alt="Boards carried in a tote between stations” />

What Damage Occurs in Transit

The mechanisms are flexure, impact, electrostatic discharge and contamination. Flexure comes from carrying a panel by one edge, from stacking boards on top of each other and from placing a board onto a surface that is not flat. Impact comes from a board dropped onto a bench, from a trolley hitting a door frame or from a stack that topples. Discharge occurs when a board is carried without a protective container, and contamination comes from a bench, from a glove or from the tote that last held a bare panel.

Each mechanism has a different signature in the defect data. Flexure produces cracked joints and ceramic cracks near an edge; impact produces localised damage and displaced components; discharge produces intermittent failures that appear later; contamination produces coating adhesion failures and leakage. Recognising the signature is what allows the handling method to be changed. Stress control addresses the flexure half of the problem.

Totes, Trays and Carriers

A tote is the simplest protective device and the one most often misused. It should support the board across its width rather than at its edges, hold it so that it cannot slide, and be sized so that a second board cannot be stacked on top. Slots, separators or individual pockets are the standard solution, and the tote should be conductive or dissipative where static is a risk.

The tote also carries information. A label identifying the product, the work order and the operation helps the product to be routed correctly and prevents a board from being left in an unmarked location. Where the tote is used for several products, the situation should be defined clearly, because a mixed tote is a material mix waiting to happen. ESD protection and physical protection are usually provided by the same container.

Edge Support and Stacking

Where boards are carried without individual pockets, they should be supported at or near the edges, in the orientation the panel was designed for, and they should not be stacked. Stacking is the most common cause of flexure damage in transit, because the weight of the upper boards loads the lower ones and the components of one board press into the surface of the next. Even a small stack has a measurable effect on a thin panel.

Where stacking is unavoidable, a separator should be used and the stack height should be limited. The limit should be based on the board’s stiffness rather than on the height of the container, and it should be stated in the handling instruction. Where the product is thin and large, the limit may be one board per container, and the cost of the extra containers is small compared with the cost of the damage.

Conveyor Transfers

Conveyors introduce their own failure modes. A transfer between two machines that is not aligned can drop a board onto an edge or a rail, and a conveyor that is too narrow or too wide for the panel allows it to move during transport. The rails, the guides and the transfer plates should be adjusted for the panel and checked at changeover rather than left from the previous product.

Where a machine stops with a board inside, the board may sit on the conveyor under heat or load for longer than intended. The response should be defined: how long a board may remain, whether it must be removed and what happens to the boards that were in the oven at the time. Without a rule, decisions are made individually and inconsistently. Assembly handling practice covers the same ground from the static side.

Manual Handling Rules

The rules should be short and specific: carry a panel by two edges, never by one corner; do not place a board on a bench without a mat; do not stack boards; use the tote even for a short move. Rules that are long, or that require equipment the operator does not have, will be ignored, and the ignoring will be invisible until the defects appear.

Gloves are part of the same question. Cotton gloves protect the board from oils but shed fibres; nitrile gloves protect the surface but can hold a charge; finger cots are common in assembly and must be selected for the task. The choice should be stated in the procedure for the operation rather than left to the individual, since the wrong glove can be worse than none. Visual inspection should include handling damage in its criteria.

Work in Progress Storage

Partially built assemblies spend a significant time waiting, and the storage conditions during that wait are part of the handling process. A board waiting after printing has paste that can slump or dry; one waiting after reflow may be exposed to moisture; one waiting before coating has a surface that can be contaminated. Each of these has a time limit, and the limit should be defined and visible at the station.

The storage position matters as much as the container. A shelf that is dusty, a trolley that is pushed against a wall or a queue that is located under a dripping extraction duct all create defects that the process never sees. Walking the route with the product, from printing to packing, and looking at where things are actually left, is the most effective way to find these problems.

Traceability and Attribution

Traceability is what makes a handling problem visible rather than mysterious. Where each movement is recorded against the work order, a defect cluster can be traced to the operation and the time, and the handling method at that point can be examined. Without it, the damage is attributed to the process that detected it, which is rarely the process that caused it.

Photographs help. A reference photograph of the correct arrangement in a tote, on a trolley or on a conveyor transfer removes the ambiguity from the instruction, and it allows a supervisor to check the arrangement at a glance. The same photograph makes the standard trainable for a new operator. Batch records and the handling standard together turn the transport step into a controlled process.

FAQ

Why is stacking boards a problem? The weight flexes the lower boards and their components press into the surface of the next one. Even a small stack damages a thin panel.

What is the right way to carry a panel? By two edges, with both hands, in an orientation that does not bend the board. Never by a single corner.

Can a tote be used for more than one product? Only with clear identification and a rule about what is in it. Mixed totes are a material mix waiting to happen.

How do I find a handling problem? Walk the route, look at where the product actually waits, and use the traceability record to link the defects to the operation.