Gluing is an important process used in PCB fabrication and assembly for functions ranging from laminate bonding to strain relief. Selecting the proper adhesive or glue for the application helps ensure strong, reliable mechanical connections on printed circuit boards. This article provides an overview of the key uses of PCB glue as well as glue material properties and common glue types.
PCB Gluing Applications
Glue serves a variety of roles in PCB manufacturing:
- Laminate bonding – Bonds layers of fibreglass in multilayer PCBs
- Component attach – Glues components like resistors or capacitors to the PCB
- Wire tacking – Temporary bonding of wires before soldering
- Strain relief – Reinforces soldered connections against vibration/shock
- Edge bonding – Bonds the edge of flex PCB layers
- Masking – Protective coating over components or traces
- Thermal interface – Glues heat sinks to devices
Choosing a PCB glue optimized for the specific application ensures the adhesive meets required performance criteria.
Glue Material Properties
PCB glues exhibit a range of material characteristics that determine their suitability for particular applications:
Bond Strength
- Shear strength – Ability to withstand lateral force
- Tensile strength – Withstand pulling/stretching force
- Impact resistance – Absorb sudden impacts without breaking bond
Cure Process
- Room temperature cure – Cures through oxidation at room temperature
- UV light cure – Cures quickly under UV exposure
- Heat cure – Cures at elevated temperature
Thermal Properties
- Operating temperature range
- Glass transition temperature
- Coefficient of thermal expansion
- Thermal conductivity
Electrical Properties
- Dielectric strength – Resists electrical breakdown under voltage
- Volume resistivity – Resists conduction of electricity
- Dielectric constant – Ability to store charge in an electric field
Outgassing – Release of gaseous vapors during cure. Important for aerospace applications.
Reworkability – Ability to detach/rework bonds for repair needs
PCB Glue Types
Here are some of the common adhesive types used in PCB fabrication and assembly.
Epoxy
Epoxies are the primary adhesives used to laminate multilayer PCBs. They cure through a chemical reaction between epoxide resin and a curative hardener. Key properties:
- Exceptional bond strength and temperature resistance
- Low outgassing and high dielectric strength
- Long working life for easier application
Epoxies come in a variety of formulations tuned for flexibility, thermal shock resistance, etc.
Acrylic
Acrylic adhesives cure through exposure to ultraviolet radiation. They are often used for component attachment on the PCB surface. Benefits include:
- Cure rapidly under UV light
- Room temperature storage before curing
- Good dielectric and thermal properties
Cyanoacrylate
Cyanoacrylates, or super glues, are fast-curing adhesives used for wire tacking and temporary bonding during assembly. Properties:
- Extremely rapid room temperature cure
- Low viscosity for wicking into joints
- Ability to cure with minimal moisture
- High shear and impact strength
CA glues provide quick, strong, temporary bonds.
Silicone
Silicone adhesives cure at room temperature through reaction with moisture in the air. Applications include:
- Flexible strain relief for cables or connectors
- Thermal insulation or heat transfer
- Edge bonding of conformal electronics
- Masking sensitive components on the PCB
Silicones provide good flexibility, dielectric strength, and thermal conductivity.
Urethane
Urethane adhesives cure with moisture at room temperature. They are used when flexibility is needed:
- Bonding rigid and flexible circuits
- Absorbing vibration, shock, and stress
- Edge sealing flexible PCBs
- Adhering metal component tabs
Urethanes have good impact and chemical resistance.
Selecting a PCB Glue
Factors to consider when selecting an appropriate PCB glue include:
Strength – Tensile, shear, impact needs
Flexibility – Rigid or flexible cured bond
Temperature Range – Max operating temperature
Cure Process – Heat, UV, room temperature
Dielectric Properties – Dielectric strength, resistance
Conductivity – Thermal and/or electrical
Chemical Resistance – Solvent, moisture, etc.
Outgassing – For vacuum or aerospace environments
Reworkability – May need temporary or removable bond
Discuss application requirements with glue suppliers to identify the best adhesive product fit.
PCB Glue Application Methods
Common methods for applying PCB glues include:
- Dispensing – Depositing precise dots or lines through needles
- Screen Printing – Using a stencil to print adhesive
- Roller Coating – Rolling a thin adhesive film onto bonding surfaces
- Spraying – Aerosol spraying in open or controlled environments
- Brushing – Manual application with brushes
Automated precision dispensing or printing ensures consistency and minimizes waste.
Quality Control
To achieve reliable, consistent bonds, PCB gluing processes require controls including:
- Testing bond strength of each batch with destructive tests
- Monitoring adhesive viscosity, especially for dispensed dots
- Keeping cold storage within specified temperature range
- Avoiding exposure to moisture before application
- Using glue within recommended shelf life
- Curing bonds fully with thermal ramps or UV cycles
- Inspecting visually for complete coverage without voids
- Tracking process parameters like time, temperature, pressure
Like soldering, gluing is a manufacturing process requiring close monitoring and control.
Conclusion
Gluing is a critical process used across PCB fabrication, component attachment, wire bonding, and protecting assemblies. The wide range of PCB glues available allows selecting formulations optimized for specific applications and performance requirements. Keeping gluing processes under tight quality control ensures boards with strong, reliable adhesive bonds.
PCB Glue FAQ
Q: What are some key considerations when selecting a PCB laminate bonding glue?
A: Matching Tg, thermal conductivity, dielectric properties, temperature resistance, and flexibility needs of the board. Also consider resin flow viscosity and working life.
Q: How is cured glue reworked on a PCB?
A: Removing cured glue mechanically can damage boards. Rework generally involves heating to soften the glue for removal. Laser ablation can also detach glue.
Q: What processes can help improve adhesion of PCB glues?
A: Surface roughening through chemical or mechanical abrasion gives more surface area. Plasma surface activation also improves bond strength. Match coefficients of thermal expansion.
Q: What safety precautions are important when working with PCB glues?
A: Adhesive fumes require good ventilation. Cured blobs can be sharp. Cured cyanoacrylates generate heat. Follow all material safety datasheet (MSDS) guidelines.
Q: How is PCB glue viscosity monitored and controlled?
A: Viscometers measure viscosity. Adhesives are kept in cold storage to inhibit curing and maintain viscosity. Dispense process parameters may need adjustment to account for viscosity shifts over adhesive lifetime.
Uses of PCB glue on electronics
The electronic industry largely depends on printed circuit boards as the main components. The PCB utilizes adhesive materials in encapsulating components, conformal coating, wire tacking, and bonding surface-mount components.
A distinctive PCB is a multi-overlay built-up plastic board with a defensive plastic covering. At first, manufacturers used hardware to cover boards. They interconnected multi-facet boards ‘thru-hole innovation using drilled holes. Component and board scaling down prompted ‘surface-mount innovation’ during the 1980s. With surface-mount innovation, segment contacts are bound straightforwardly to pad sections on the outside of the board. It made it conceivable to dispose of through-board connections and drilled openings.
There is significant utilization for PCB glue, basically natural, are as per the following:
- Conformal coating of circuit boards
- Potting and encapsulating electronic components
- Wire tacking
- Bonding of surface-mount components (SMCs)
Bonding activities
- Conformal coatings
While it is not rigorously the aftereffect of a glue holding measure, you can use similar substance kinds of gum. For example, silicones, acrylics, polyurethanes, and epoxy glue for PCB. The point is to deliver a covering that certainly sticks to and covers all the board and its parts. A conformal covering is commonly used to shield the board from natural factors, for example,
- Short circuits.
- Dampness and mold changes in help temperature (ordinarily from – 40ºC to +200ºC)
- Corrosion
Conformally covered PCBs are shielded from natural harm and mechanical and electrical obstruction.
- Encapsulation and potting
It is a strategy for covering little surfaces or spaces with a material that will shield parts from physical and ecological harm. Encapsulation parts likewise give extra protection ability.
Potting compounds typically display excellent synthetic properties and high grip to plastics and metals, these being the materials of development of the holders and the parts.
Regular saps utilized for encapsulating are acrylics, silicones, polyurethanes, and epoxies, the last as a rule being UV-relieving definitions.
Similarly, there are different techniques for exemplifying electronic segments, to be specific projecting and trim. Projecting utilizes similar glue as preparing, albeit the compartment is generally eliminated after the pitch has been relieved.
Dissimilar to the potting cycle where the holder turns into a fundamental piece of the segment. For the most part, Embellishment includes the infusion of pre-dissolved thermoplastic pitches into a form containing the electronic components or hardware.
- Wire-tacking glues
Connection using wires is normal on PCBs. The utilization of wires permits substitution as well as an increase of printed wiring on the PCB. A portion of the explanations behind this is as per the following:
- To fix board harm or defeat the impacts of ill-advised assembling.
- To redesign or change a PCB.
- To conquer a plan imperfection found during board testing.
Typically, a protected wire is stripped and bound at each finish to cushions and part drives, at that point fortified or marked to the board substrate. The holding keeps the wire from moving around and goes about as an underlying glue in conditions where vibration could happen.
The glue that one can choose for wire attaching incorporates light-reparable acrylics, epoxies, and cyanoacrylates. Practically speaking, cyanoacrylates are generally utilized, regularly related to a suitable activator to speed the fixed time to around half a minute.
- Surface-mount devices (chip holding)
Surface-mount devices (SMDs) are set on little dots or spots of uncured glue and afterward relieved set up by warming or openness to UV radiation. It gets the SMDs solidly set up during resulting measure tasks like leaded-gadget addition or cleaning until they can be fastened to the board’s patch pads. Surface-mount glue can serve two capacities: they go about as a handling help (for example, holding a section briefly until it tends to be for all time appended by patching). They can likewise give pressure alleviation to bind connection during administration to forestall untimely disappointment of the electrical bonds. Subsequent to soldering, the now repetitive glue should not any effect on the hardware at all.
To meet the necessities for effectively holding SMDs, the accompanying properties are expected of the glue:
- Good electrical properties after curing
- High strength and good flexibility
- Non-slumping during the heated cure cycle
- Rapid curing
- High wet strength
- Non-stringing
- Suitability for high-speed dispensing of very small dots of consistent profile and size
- Long shelf life
Contingent upon the specific capacity of the surface-mount glue, it tends to be electrically conductive, electrically non-conductive, and thermally conductive. Three compound kinds of glue are generally utilized for surface-mount segment holding: acrylics, epoxy glue, and urethane acrylates. These glue variants, along with different sorts utilized in hardware applications, are talked about in more prominent detail beneath.
Preferably, surface-mount glues should be of the single component type. It maintains a strategic distance from pot-life issues, air entanglement, and changes in thickness ordinarily connected with double or multi-part frameworks. Usually, the glues will fix inside two minutes at raised temperatures alright for PCBs and related parts.
Types of glue for circuit boards
We need to consider three diverse handling stages while choosing circuit board adhesive applications. They include the solid-material or cured phase, the curing (transitional) phase, and the liquid-resin or uncured phase. The presentation of the solid-material adhesive is eventually the most significant since it enhances quality.
The technique for applying the PCB component glue is critical, specifically given the need to guarantee that the right sum is applied in the right spot. Significant techniques for applying glues in hardware applications are syringe application, pin transfer, and screen printing. Syringe application is presumably the most famous strategy, ordinarily via electro-pneumatically controlled syringes for moderate creation of a wide range of kinds of PCB.
The different kinds of glue for circuit boards include:
- Ultraviolet curing glues
Light-curing encapsulants, coatings, and adhesives are being utilized in the hardware producing industry, expanding recurrence since they meet the necessities for materials and preparing inside this industry. Those elements incorporate ecological protection policies (environmentally damaging solvents and added substances are not needed), fabricating yield improvement, and item cost. Light-curing glues are easy to utilize and are immediately relieved without the requirement for raised temperature relieving.
The glues are regularly acrylic-based details and contain photograph initiators that actuated by bright radiation, structure-free revolutionaries to start the polymer-shaping (relieving) measure. Bright light should have the option to infiltrate into the uncured sap, a downside of light-curing glues. Stores of pitch that are dimly shaded, blocked off, or thick are hard to fix.
- Thermally conductive glues
Scaling down electronic hardware may bring about issues of heat arise, which can cause untimely malfunction of electronic parts if their most fantastic working temperature is surpassed. Thermally conductive glue can give a heat-directing way, securing semiconductors, diodes, or other force gadgets to appropriate heat sinks to guarantee such a temperature does not happen.
Non-metallic (insulating) or metallic (electrically conductive) powders are mixed into the glue plan to make high-thickness glues, which are exceptionally thermally conductive. The most well-known hot glue PCB is formed with acrylics, silicone, and epoxy.
- Electrically conductive PCB adhesive
By their inclination, most glues, both natural and inorganic, are not electrically conductive. It applies to the principle types utilized in electronic applications. They include cyanoacrylates, urethane acrylates, silicones, cyanoacrylates, acrylics, and epoxy glue for PCB. Notwithstanding, in numerous applications, including coordinated circuits and surface-mount gadgets, electrically conductive glues are required.
There are two sorts of electrically conductive glues, which are anisotropic and isotropic. Anisotropic glues are good conductors in all directions. However, an isotropic glue conducts in the upward (z-pivot) heading just and is in this way uni-directional. The isotropic glues loan themselves to almost negligible difference interconnection. It ought to be noticed that valuable as conductive glues are, they cannot be essentially ‘dropped in’ as patch choices. They are bad with tin or aluminum, nor where there are enormous holes or where they are probably going to be presented to wet conditions in help.
The typical method of changing non-conductive glues over to electrically conductive materials is to add reasonable filler to the base material. Generally, the last is an epoxy pitch. Commonplace fillers used to give electrical conductivity are carbon, nickel, and silver. Silver is the most broadly utilized. The conductive glues themselves are either in a fluid or pre-structure.
- Other glue types
The glues referenced above are the significant sorts utilized in ordinary gadgets fabricating strategies. There are others, nonetheless, which are still generally utilized:
- Polyimides: These are high-temperature saps (enduring up to 300ºC or somewhere in the vicinity) utilized in high technology hardware applications (ordinarily aviation) for wire coatings and adaptable circuits. They usually are utilized as polyamic corrosive forerunners and require troublesome and delayed restoring cycles before shaping the average adaptable, heat-safe polyamide material.
- Silicone resins: More a sealant than a primary glue, silicone sap is utilized as an encapsulant just as for conformal covering. Silicone pitches have excellent low and high warmth resilience (regularly – 60ºC to +200ºC) yet can mess up optional activities on account of the arrival of low-sub-atomic weight silicone compounds, which sully surfaces over a wide region.
- Cyanoacrylates: These have effectively been referenced for their utilization in wire-attaching applications. Cyanoacrylates are single-part glues, which fix quickly when presented to dampness noticeable all around. The utilization of these glues with an activator speeds up the relieving interaction significantly more.
There are significantly more glues, which have discovered use in hardware applications, and without a doubt, more will follow. Nonetheless, the sorts referenced above are grounded and generally utilized and structure a fundamental piece of the gadgets fabricating industry.
Conclusions
The gadgets market involves a wide range of enterprises, including media communications, customer, PC, and car areas, utilizing the PCB as the fundamental structure block for their items. Several years ago, the measure of glues utilized in creating PCBs and other electronic parts was insignificant. Presently the shortfall of glues from gadgets producing is incomprehensible. Natural, wellbeing, cost, and assembling speed are driving variables for the proceeding and always growing utilization of glues in the business.
The days when soldering was the elite joining technique in PCBA have a distant memory. The point currently is to zero in on the utilization of glues as patch choices. There is still some best approach, as the glue should assume control over the mechanical properties of the bind and be electrically and thermally conductive to a serious level.
