Calculating microspheres per gram

During scientific experiment design and analysis it is common to need to know the number of spheres per gram of dry material.  We have put together the table below to help speed up the process.

If you have material of a density different from those listed in the table, divide the number of spheres per gram in the density ~1.0 g/cc column by the true particle density of your material to get an estimate of the number of spheres per gram.

Note: This table assumes the mean diameter is half way between the upper and lower size.

Monodisperse Silica Microspheres

Scientists are always pushing the limits, and looking for more precise products and equipment to enable the next technology.   In an effort to provide those scientists with the right tools Cospheric LLC has added monodisperse silica microspheres to their broad product line.

Silica particles are now available in distributions of less than 10% CV in the sizes of 1.0 micron, 4 micron and 8 micron.

Silica Microsphere Products now available:

SIO2MS 1.0um  <10% CV

SIO2MS 4.0um <10% CV

SIO2MS 8.0um <10% CV

SIO2MS 4-6um  (2-19um range)

Microspheres as bond line spacers in epoxies

Today’s electronics are demanding tighter and tighter tolerances, and the assembly of many items require holding precise spacing between parts during assembly.  The spherical shape and precise sizes available make microspheres the ideal candidate as a precision spacer in various liquid adhesives and epoxies.

Important considerations:

1) The actual bond line will correspond to the largest spheres, not the average size.  Narrow size ranges of a few micron ensure the proper gap is maintained.

• If a 30um gap is required use a spacer grade size range of 27-30 micron.
• If a 40um gap is required use a spacer grade size range of 37-40 micron.
• If a 53um gap is required use a spacer grade size range of 50-53 micron.

3) Functionality gained from using different materials.

• Glass offers the best mechanical and chemical stability at a wide range of temperatures.
• Plastic such as PMMA can be used where some deformation is desirable.
• Metal coated glass spheres can be used where conductivity is desirable.
• Hollow Glass spheres can be used where assembly pressures are low, and reduced thermal conductivity is desired, available as uncoated hollow glass or silver coated hollow glass spheres.

4) The importance of sphere loading (% spheres by volume in the adhesive)

• Theoretical maximum loading by volume for a monolayer is 61%
• A mixture of about 5% by volume should work for most applications.
• Narrow bond lines with high assembly forces will require higher loadings
• Low crush strength spheres will require higher loadings.
• Proper dispersion in the adhesive will help to minimize the loading needed.

5) Adhesive / Epoxy selection

• High viscosity epoxies will help maintain sphere dispersion.
• For best results choose an adhesive that adheres to the spheres and the base material.
• Long pot-life materials work best, as they allow excess adhesive to flow out of the bond line during assembly.

6) Spacer Availability – Cospheric LLC stocks a wide variety of sizes and materials, and can custom produce spacer grade microspheres for your application.

• Spacer Grade Solid Glass Spheres, narrow 3um ranges, >95% in range, 22-53 micron
• Silver Coated Solid Glass Spheres, >90% in range, 22-110 micron sizes
• Soda Lime Glass Spheres, >90% in range, 27 micron to 3.4 mm sizes
• Solid PMMA Spheres, >90% in range, 20-150um sizes

Applications for Bond Line Spacers

Spacer Grade Glass Microspheres are presently used in gas plasma displays, automotive mirrors, electronic displays, flip chip technology, filters, sporting goods equipment, calibration standards and transformer manufacturing.  Every day engineers are finding new and innovative uses for bond line spacers.  One area that has had the most publications is in die attachment in the semi-conductor industry, a particularly interesting area is in using spacers for building multi-die packages. Continue reading “Microspheres as bond line spacers in epoxies” »

Advantages of Borosilicate Glass Microspheres in 0.03mm to 0.2mm sizing

BSGMS 63-75 micron at 40x magnification

High quality glass microspheres for research and development are always in high demand.  In an effort to better serve scientists Cospheric recently added a complete line of high quality borosilicate microspheres, and microbeads.

Borosilicate glass offers  advantages over standard soda lime glass microbeads.

• Roundness is >90%   (Soda lime >85%)
• Density is the lowest of most glasses at 2.2g/cc  (Soda Lime 2.5g/cc)
• Very low thermal expansion coefficient  32×10^-7/°C   (for 30-300°C)   (Soda Lime:  90×10^-7/°C)

The high roundness, and low thermal expansion make borosilicate spheres an excellent candidate for use as spacers in epoxy bond lines, or other applications which require stability over a wide temperature range.

Borosilicate glass spheres are now offered in narrow size ranges from 0.03mm to 0.2mm with greater than 90% of the particles in range.

Continue reading “Advantages of Borosilicate Glass Microspheres in 0.03mm to 0.2mm sizing” »

Monodisperse – Spacer Grade Microspheres

SLGMS 27-30um 40x

Scientists are constantly looking for narrower particle size distributions (monodispersed) of microspheres to help increase the consistency and correlation between theoretical models and verification experiments.  In an effort to fill the increasing demand for these particles Cospheric has launched a new line of spacer grade microspheres.

Monodisperse microspheres are currently offered in diameters of:   21-24um, 23-26um, 25-28um, 27-30um, 29-32um, 31-34um, 33-36um, 35-38um, 37-40um, 50-53um

Manufactured with Soda Lime Glass, monodisperse spheres are excellent for spacing epoxy bond lines that will experience high temperature.

• Degree of Roundness: >90%
• Particles in Size Range: >95%
• Density: ~2.52g/cc
• Index of refraction: ~1.51
• Softening Temperature: 730°C