Ferrite core halves may be bonded to prevent movement, reduce noise, support handling, or secure an assembly. Ferrite is brittle and magnetically sensitive to mechanical stress. A reliable ferrite core bonding process must hold the assembly without cracking the core, contaminating mating surfaces or gaps, changing inductance, or degrading under thermal cycling.
Adhesive selection
Epoxy, silicone, urethane, cyanoacrylate, and other adhesives differ in modulus, glass-transition temperature, cure shrinkage, thermal expansion, moisture behavior, flammability, dielectric properties, and compatibility. A rigid adhesive can transmit stress as ferrite, bobbin, and PCB expand differently. A flexible adhesive may creep.
Selection should match temperature, cycles, vibration, humidity, life, cure, and rework. Individual temperature rating is not proof of insulation-system compatibility.
Keep adhesive out of magnetic interfaces
For ungapped cores, adhesive between mating faces creates an unintended gap and lowers permeability. For gapped cores, contamination changes the calibrated gap. Bonding is often placed on external surfaces, clips, or designated recesses.
Squeeze-out can enter the winding, bobbin, gap, or creepage path. Dispense volume, location, viscosity, temperature, and clamp pressure should limit migration.
Surface preparation
Dust, grinding residue, oil, release agent, fingerprints, and moisture reduce adhesion. Cleaning should use a validated method compatible with ferrite coating, bobbin, winding insulation, and adhesive. Define maximum open time and clean handling.
Bond-line thickness and clamp force
Too little adhesive starves the joint; too much increases movement, cure heat, and squeeze-out. Spacers, fixture stops, or dispense-volume control can set thickness.
Clamp force must seat the core without fracture or bobbin distortion. Excess force can chip ferrite, change a gap, or stress the PCB. The fixture should distribute load and accommodate tolerance.
Cure control
Mix ratio, dispense time, pot life, material temperature, humidity, cure temperature, ramp, and dwell determine properties. Oven air may differ from adhesive temperature. Cure shrinkage can pull on core and windings.
Record batch, mix, dispense, fixture, and cure data. Incomplete mixing can leave soft regions that pass initial handling but fail later.
Magnetic effects
Core stress can change permeability and loss. Measure magnetizing inductance, AL value, leakage, loss where relevant, and acoustic behavior before and after qualification. Production tests should detect adhesive contamination or incorrect seating.
Qualification
- Visual criteria for bead location, squeeze-out, cracks, and contamination.
- Mechanical retention under defined loading.
- Thermal cycling, aging, humidity, vibration, and shock.
- Magnetic and electrical tests before and after exposure.
- Destructive audits for bond-line quality.
- Change control for adhesive, supplier, fixture, and cure.
BaoHui Tech treats adhesive and process as part of transformer construction. A supplier substitution or faster cure requires review because it can change mechanical and magnetic performance.
Frequently asked questions
Can glue be placed between mating faces?
Only when the design explicitly includes that bond line in the magnetic gap and qualification.
Does stronger adhesive always help?
No. Excess stiffness or cure shrinkage can increase stress during thermal cycling.