Learn about underfill materials and processes for BGA and CSP assembly.
Introduction to Underfill Technology
Underfill technology has become essential for maintaining electronic assembly reliability as BGA and CSP devices have become ubiquitous. Underfill reduces stress by approximately 80% compared to ununderfilled assemblies.
Capillary Flow Underfills
Capillary flow underfills are the most widely used, applied after solder reflow to fill the gap through capillary action. Filler content typically ranges from 50-70% by weight.
No-Flow Underfills
No-flow underfills eliminate the separate application step by combining solder paste and underfill. Both solder joint formation and underfill cure occur in a single process step.
Molded Underfill Technology
Molded underfill (MUF) encapsulates the entire package, providing not only stress relief but also mechanical protection and improved thermal management.
| Property | Capillary | No-Flow | Molded |
|---|---|---|---|
| Process Step | After reflow | With reflow | After reflow |
| Gap Fill (μm) | 50-150 | 50-100 | Any |
- Select underfill technology based on reliability requirements
- Optimize gap height and filler content
Frequently Asked Questions
Why is underfill necessary for BGAs?
Underfill compensates for thermal expansion mismatch, distributing stress evenly across solder joints.
