Printed circuit boards pass through several demanding stages during electronics manufacturing. One of the most challenging environments for identification labels is the soldering process, where circuit boards are exposed to high temperatures and rapid heating cycles.
Labels that perform perfectly well in general industrial environments can quickly fail when exposed to soldering temperatures. They may shrink, discolour, lose adhesion or cause barcode distortion that prevents reliable scanning.
For manufacturers that rely on traceability, selecting labels that can survive soldering is essential. The right combination of label material, adhesive and printing method ensures that PCB identification labels remain readable throughout production and beyond.
Speak to a labelling expert at Zygology Systems on 01628 520440 or email info@zygology.co.uk.
In this guide
- Why soldering is challenging for labels
- Reflow and wave soldering processes
- Label materials that survive soldering
- Adhesives for high-temperature labels
- Printing methods for durable PCB labels
- Label size and barcode readability
- Multiple heating cycles in PCB manufacturing
- Common label failures during soldering
- Choosing the right label for soldering processes
Why Soldering Is Challenging for Labels
Soldering is a critical stage of PCB manufacturing where electronic components are permanently attached to the circuit board. During this stage, boards are exposed to rapid temperature increases that can exceed 200°C.
Many standard label materials cannot tolerate these temperatures. When exposed to soldering heat, labels may shrink, curl or become brittle. Adhesives can soften and lose bonding strength, causing the label to lift or detach.
In addition to heat exposure, soldering processes can introduce other stresses that affect labels, including:
- rapid temperature changes
- flux residues and cleaning chemicals
- handling during assembly
- airflow and heating gradients within ovens
These conditions make soldering one of the most demanding stages for PCB identification labels.
Reflow and Wave Soldering Processes
Two of the most common soldering processes used in electronics manufacturing are reflow soldering and wave soldering. Both processes expose the circuit board to elevated temperatures that can challenge label materials.
In reflow soldering, solder paste is applied to the PCB and the board is passed through a reflow oven where the temperature gradually increases before reaching a peak temperature that melts the solder.
Wave soldering uses a wave of molten solder to form connections on the underside of the board. This process can expose labels to intense localised heat depending on their position on the PCB.
In both cases, labels must maintain their shape and remain securely attached throughout the heating cycle.
If the label shrinks or distorts even slightly, barcode readability may be affected. This is particularly important where labels contain small data matrix or QR codes used for traceability.
Label Materials That Survive Soldering
One of the most widely used materials for high-temperature PCB labels is polyimide. Polyimide films offer excellent thermal stability and are specifically designed for environments where conventional materials would fail.
Polyimide labels are commonly used because they:
- maintain dimensional stability at high temperatures
- resist shrinking or distortion
- perform reliably during soldering cycles
- support durable barcode printing
Our guide to polyimide labels for electronics manufacturing explains in more detail why this material is widely used for PCB identification.
In contrast, materials such as polyester may be suitable for many industrial labels but are generally not designed to tolerate the extreme temperatures involved in soldering processes.
Adhesives for High-Temperature Labels
Even when the face material is capable of surviving soldering temperatures, the adhesive must also be suitable for the environment.
An adhesive that softens or degrades at high temperatures can cause the label to lift, bubble or detach during manufacturing.
High-temperature PCB labels therefore require adhesives designed to:
- maintain adhesion at elevated temperatures
- bond securely to PCB surfaces
- resist cleaning chemicals
- remain stable after repeated heating cycles
Adhesive selection is an important part of specifying labels for electronics manufacturing.
Speak to a labelling expert at Zygology Systems on 01628 520440 or email info@zygology.co.uk.
Printing Methods for Durable PCB Labels
In addition to selecting the correct material and adhesive, the printing method must also produce markings that can survive soldering processes.
For demanding environments, thermal transfer printing using resin ribbons is commonly recommended because it produces highly durable print.
Resin ribbons are designed to resist:
- high temperatures
- chemical exposure
- abrasion during handling
This ensures that barcodes and serial numbers remain readable even after the board has passed through several manufacturing stages.
Our guide to thermal transfer vs direct thermal labels explains why thermal transfer printing is typically preferred for industrial durability.
Label Size and Barcode Readability
PCB labels are often extremely small. As electronics become more compact, the available space for identification labels becomes increasingly limited.
Despite their small size, these labels must still contain readable barcodes or QR codes that can be scanned during production and servicing.
When labels are exposed to high temperatures, even slight material distortion can affect barcode readability. This is why dimensional stability is so important for PCB labels.
We explore this topic further in our guides to how small a QR code label can be and barcode readability problems in small labels.
Multiple Heating Cycles in PCB Manufacturing
Some PCBs may pass through heating stages more than once during manufacturing. For example, boards may undergo multiple soldering passes or additional rework processes.
This means the label must survive repeated heating cycles rather than a single exposure to high temperature.
When specifying labels, engineers should consider not only the peak temperature of the soldering process but also how many times the label will be exposed to that temperature.
A label that survives a single pass may not perform reliably if exposed repeatedly to the same conditions.
Common Label Failures During Soldering
When unsuitable materials are used, several types of label failure can occur during soldering.
Common issues include:
- label shrinkage that distorts barcode dimensions
- adhesive softening that causes the label to lift
- discolouration caused by heat exposure
- barcode print degradation
These failures can lead to unreadable labels and lost traceability information.
Our guide to why PCB labels fail in electronics manufacturing explains several of these problems in more detail.
Choosing the Right Label for Soldering Processes
Selecting labels that survive soldering involves considering several factors, including:
- maximum temperature exposure
- number of heating cycles
- PCB surface material
- label size and barcode requirements
- chemical exposure during cleaning
By specifying the correct combination of material, adhesive and printing method, manufacturers can ensure that PCB labels remain readable and securely attached throughout the production process.
Our guide to how to specify labels for electronics manufacturing provides a broader overview of the label selection process.
Need Help Choosing Labels for Soldering Processes?
PCB labels must survive some of the most demanding conditions found in electronics manufacturing. Selecting the correct label construction is essential for reliable traceability.
Speak to a labelling expert at Zygology Systems today:
Call 01628 520440
Email info@zygology.co.uk
Zygology Systems supplies high quality custom labels made in the UK and tailored to demanding industrial environments including PCB identification labels and high-temperature polyimide labels.
