Electronics Assembly Knowledge, Vision & Wisdom
Underfill Limitations for Future Packages
Underfill Limitations for Future Packages
The paper addresses the issue of underfill as die thickness diminishes, the interconnection bumps get smaller and their number increases.
Materials Tech

Authored By:
Horatio Quinones and Tom Ratledge
Carlsbad, CA, USA
,{url:'http://www.circuitinsight.com/videos/programs_final.mp4'}], clip:{autoBuffering:true, autoPlay:true, scaling:'scale' } }).ipad();
The capillary underfill (CUF) although a well established manufacturing assembly process, is being challenged as die thickness diminishes, the interconnection (bumps) get smaller and their number increases. Denser populated packages demand very tight tolerances for keep out zones (KOZ); the total package thickness challenges the process throughput since die contamination from underfill fluid is not allowed and multiple fluid dispense passes may be needed.

All this challenges translate in lower capillary surface energies, increase in fluid flow drag, smaller particle size fluid that often results in increase in viscosity and therefore slow flow-out-times. The present work addresses these issues. A series of mathematical models based on surface energy evolution for CUF accounting for these new geometries and processes is proposed. In particular the problem of component proximity is and the gap topology issues are studied. Experimental data for CUF in the presence of these future assembly demands is shown. Although there are practical physical limitations for the CUF as experienced today if one were to implement it for future packages, new hybrid CUF methods that overcome such shortcoming are recommended
A comprehensive analysis of capillary fluid flow has been presented and validated by actual data. The coupling of molecular forces adhesion and cohesive in nature and the minimization of surfaces, as in the case of elastic membranes that yield Willmore critical surfaces in the differential geometry scheme gives an adequate way to model capillary fluid flow. These solutions were obtain in a way by perturbation theory where Variational of the functional derived from Poisson integral formulation mimic very closely the observation of capillary fluid flow under various boundary conditions that included several different geometries.

For dispensing in presence of tight spacing and high density packages, the Jetting technology lends itself in a very transparent and practical manner. Above results can be used as guidelines in situations where uneven surfaces and arrays are present and capillary flow is used. Design rules for packaging design need to include the capillary physics present during underfilling and fluid dispensing in general.
Initially Published in the SMTA Proceedings
Submit A Comment

Comments are reviewed prior to posting. Please avoid discussion of pricing or recommendations for specific products. You must include your full name to have your comments posted. We will not post your email address.

Your Name






Please type the number displayed into the box. If you receive an error, you may need to refresh the page and resubmit the information.

Related Programs
bullet Selective Removal of Conformal Coatings by Pulsed Ultraviolet Lasers
bullet Effectiveness of Conformal Coat to Prevent Corrosion of Terminals
bullet A Robot's Place in SMT
bullet Conformal Coating in Nitrogen Environment
bullet Lower Temperature Solder Joint Encapsulant
bullet Conformal Coating Recommendation
bullet Thermally, Electrically Conductive Adhesive to Control Heat in PCBs
bullet SMT Adhesive Inspection
bullet How to Protect Internal Circuitry from a Harsh Environment
bullet Signal Loss in a High Speed High Frequency Transmission Line
More Related Programs