Fluxes
Indium Corporation is a developer, manufacturer, and global supplier of: specialty solders (including solder paste, preforms, spheres, columns, wire, tubing, ribbon, and foil), fluxes, electrically-conductive adhesives, inorganic, indium compounds (including indium oxide, indium-tin oxide, indium hydroxide, and indium chloride), fusible alloys, indium-containing fabrications of all types, and pure indium (from commercial grade through high-purity grade).
Fluxes Ideal for Micro-Array Attach
Indium Corporation design and manufactures innovative flux materials for direct attach of array packages including flip-chip, chip-scale and micro-BGA packages. Flip-Chip Fluxes and TacFluxes are designed to meet the processing, soldering and residue demands of our customers. During the attach process, the micro-array package is usually dipped into flux that has been cut by a blade into a thin, consistent film. Application of flux in appropriate quantities to an array of small solder-bumps (0.004-inch diameter is common) requires that a flux have the correct wetting properties, viscosity, and texture.
Ideally, flux should be applied in a thin film only to the solder bumps. Because the residue concerns (glob-top or underfill adherence), dipping the entire package in flux is not acceptable. Consequently, any flux suitable for a flip-chip process must have the correct viscosity at machine operating conditions (temperature plays a critical role in flux viscosity and tack). A high viscosity may leave peaks on the bottom of the bumps (too much flux coating the balls) while a low viscosity could wick up and over the package (flux in the wrong location) or could leave an insufficient deposition on the balls (too little flux).
Viscosity alone is not a sufficient determinant. Tack and flux wetting also play important roles in micro-array package attach. If the flux is too tacky, a great deal could stick to the bumps (too much flux), or the package could get pulled off the vacuum nozzle. Flux wetting or spread is important because it will affect the quantity and location of the flux.
Tack and viscosity combine to affect the texture of a flux. Although most fluxes are homogeneous and have a smooth consistency; many can not be cut into a uniform thin film. The revolving flux reservoir has a stationary blade designed to spread the flux into an even distribution across the planar bottom on the reservoir. However, fluxes with very high tack and viscosity will often rip and leave gaps in the flux film. Conversely, a low viscosity, low tack flux will tend to pool leaving areas with excessive flux material. Both of these conditions will give poor micro-array attach package. Indium Corporation provides materials that will guarantee the consistent application of flux to all of a micro-array’s solder bumps.
Flux tack is also important for component holding. Most micro-array attach processes are very gentle and do not demand excellent holding force. However, during board handling, transfer, and reflow, numerous opportunities exist for shifting of the array package. Tack requirements will vary depending on your specific process. Indium Corporation can accommodate these different tack needs with it's line of Flip-Chip and TacFluxes.
Activity levels for micro-array attach process depend primarily on the metallizations and reflow method. Bare copper boards of heavily oxidized bumps require more activation and likely will leave substantial residue behind. Inert or vapor phase reflow systems require much less activator because oxygen is no longer attacking the flux during the heating process. Flux activation should not be a factor in joint failure. If your current process gives unreflowed (cold) solder joints, the likely cause is lack of flux on the bumps. Indium Corporation can provide you with the ideal flux to reduce or eliminate the problem on missing flux on the bumps.
No-clean residue levels and characteristics must be compatible with underfill and glob-top materials. Careful testing must be conducted with each set of materials to ensure that good adherence and complete cure are achieved.
Indium Corporation will work with you to design the right flux for your micro-array attach application. Indium Corporation's Flip-Chip Fluxes and TacFluxes will meet you manufacturing needs.
For more information on Indium Corporation's Flip-Chip Fluxes and TacFluxes, contact us by telephone at 800-4-INDIUM or 315-853-4900, or by e-mail at askus@indium.com.
