Solution

"Particle Traps" in Electronics Manufacturing: How Particle Size and Shape Data Plug Quality Gaps

On electronics production lines, some failures appear accidental but are in fact inevitable. A thick-film circuit develops open circuits after printing — under the microscope, a 10 μm silver powder agglomerate is found lodged in the screen mesh. A batch of MLCC capacitors fails voltage withstand testing — traced back to a few oversized particles in the ceramic slurry that caused localized thinning of the dielectric layer. LED packages show lower-than-expected luminous flux — the culprit is a few fibers floating in the silicone, originating from the air or containers. These cases share a common thread: the problem lies with particles invisible to the naked eye.

Mipu Technology applies laser diffraction, static image analysis, microflow imaging, and nanoparticle size analysis to particle control in electronic materials. We don't simply deliver a particle size report — we help you answer: What is that particle that shouldn't be there? Where did it come from? How do we stop it? The following sections examine typical electronic materials through real case studies, demonstrating how particle characterization plugs quality gaps.

Electronic Pastes: Screen Clogging, Open Circuits, and Oversized Particles – Tracing Back from Screen Printing to Particle Control

Scenario: A conductive silver paste supplier serving the touchscreen industry received a sudden customer complaint about open circuits in printed lines. The defects occurred randomly at a frequency of approximately 3%. The quality report showed silver paste D50 = 0.8 μm, D90 = 1.5 μm — within specifications. Yet the problem persisted.

Diagnosis: Conventional laser particle size analyzers cannot detect trace amounts of oversized particles. A combined laser particle size analyzer + microflow imaging analyzer approach was recommended. Testing revealed approximately 80 particles >5 μm per milliliter of silver paste, with irregular blocky morphology and a few elongated shapes. Further analysis traced these to wear debris from zirconia beads in the bead mill. After switching to high-purity zirconia beads and adding 200-mesh in-line filtration, oversized particles dropped to 2 particles/mL, and the open-circuit rate fell to zero.

Technical Essentials:

• Primary Material Particle Size: Laser particle size analyzers measure D10, D50, D90, and Span to ensure batch-to-batch consistency.

• Trace Oversized Particles: Microflow imaging automatically counts and images particles, distinguishing metal debris, agglomerates, and fibers.

• Morphology Impact: Low sphericity of silver powder leads to abnormal rheology; static image analysis quantifies sphericity (target >0.85).

Applicable Materials: Conductive silver paste, copper paste, nickel paste, carbon paste, MLCC electrode pastes, photovoltaic front-side and back-side silver pastes.

Spherical Silica Powder: Why Must Encapsulation Fillers Be "Round"?

Scenario: An epoxy molding compound (EMC) manufacturer found that under the same formulation, different batches of molding compound exhibited significant viscosity fluctuations during injection molding, causing chip warpage rates to jump from 0.5% to 2%. Raw material investigation revealed significant batch-to-batch variations in the sphericity of spherical silica powder.

Testing Method: Static image analysis — a 10 mg sample was spread on a slide and 100,000 particles were imaged. Outputs included:

• Mean sphericity (target >0.92)

• Proportion of particles with sphericity <0.85 (non-conforming rate should be <5%)

• Proportion of particles with aspect ratio >2

Results: The non-conforming batch had a mean sphericity of only 0.86, with 15% of particles being elliptical or rod-shaped. These non-spherical particles bridged within the resin, increasing viscosity and causing uneven filling. After adjusting the temperature profile of the flame fusion furnace, sphericity recovered to 0.94, and the warpage rate dropped.

Extension: Spherical silica powder is also used in thermal pads, underfill, coatings, and more — sphericity is equally critical in these applications.

Applicable Materials: Spherical silica powder, spherical alumina, aluminum nitride, thermally conductive fillers.

Solder Paste: Direct Correlation Between Solder Powder Sphericity and Printing Yield

Scenario: An SMT facility using Type 5 solder paste (solder powder D50 = 18 μm) experienced frequent slumping and missing deposits when printing 01005 components. The supplier's particle size report showed compliance, yet the problematic batch was unusable.

Independent Testing: Static image analysis of the solder powder morphology revealed that 9% of particles had sphericity <0.85, with 4% being acicular. In contrast, the acceptable batch had a sphericity non-conformance rate of <2%. Acicular solder particles do not roll easily under squeegee pressure, resulting in uneven paste deposition. After the supplier improved the powder manufacturing process (rapid cooling after atomization), sphericity conformance rose to 98%, and printing defects dropped from 5% to 0.6%.

Standard Reference: IPC J-STD-005 requires solder powder sphericity >0.9, with acicular particle proportion <1%.

Applicable Materials: Solder paste, copper paste, low-temperature solder pastes.

Electronic Chemicals: The "Invisible Killers" in Photoresists and Fluxes

Scenario: A PCB manufacturer observed micro-gaps on fine lines after exposure and development. Photoresist investigation: laser particle size analysis showed particle D50 = 120 nm, within specification. However, nanoparticle size analysis revealed a PDI (polydispersity index) of 0.28, indicating the presence of agglomerates. After optimizing the dispersion process (extended ultrasonication), PDI dropped to 0.09, and development defect rates fell from 4% to 0.5%.

Another Scenario: A flux produced excessive solder balls after wave soldering. Microflow imaging analysis revealed the flux contained numerous fibers and metal particles, traced to flaking from the inner walls of raw material containers. After switching to containers with polished inner walls and adding filtration, the solder balls disappeared.

Technical Solutions:

• Nanoparticles: Nanoparticle size analyzers (DLS) measure D50 and PDI, targeting PDI <0.1.

• Foreign Matter Detection: Microflow imaging automatically classifies metals, fibers, and bubbles, outputting concentration (particles/mL).

Applicable Materials: Photoresists, developers, etchants, fluxes, cleaning agents, underfill materials.

Quick Reference for Other Electronic Materials

What Mipu Technology Can Do (Not a List of Instruments, But a Solution Logic)

We do not offer a "one-size-fits-all particle size analyzer." Instead, we combine technical approaches based on your materials and production line conditions:

• Worried about oversized particles? → Combined laser diffraction + microflow imaging — one sample injection simultaneously provides distribution data and oversized particle counting with ppm-level sensitivity.

• Worried about poor morphology? → Static image analysis with 100,000-particle statistics, sphericity distribution histograms, and clear directions for process improvement.

• Worried about nano-agglomeration? → Nanoparticle size analyzer measures PDI to evaluate dispersion effectiveness, guiding ultrasonication or dispersant addition.

• Worried about foreign matter? → Microflow imaging automatically classifies particles, with retained images for traceability.

We provide full-process services from method development, SOP establishment, personnel training, to online monitoring. All data complies with IPC, SEMI, GB, and other standards — traceable and auditable.

Conclusion: Expose Particle Problems Before They Enter the Production Line