Progressive Energy Dynamics: Key to Low Standoff Cleaning

The Science of Cleaning

PED

Space under components is shrinking

Interconnect densities are increasing

Performance requirements are increasing

Lead-free & no-clean are harder to clean

Fluxes are fully filling small gaps

1. What’s the Problem ?

1. Physical properties of the cleaning agent(surface tension, density and viscosity)

2. Higher energy fluid delivery(flow rate and impact velocity)

Energy Delivered is dependent on equation for Kinetic Energy

Kinetic Energy @ the surface = mass x velosity2 @ the surface

2. Fluid Flow Theory – Cleaning Small Gaps

Depends on 2 things - - -

Δp = 2γ cosθ / R

Interfacial pressure differential calculation

γ = surface tension

R = radius meniscus

Θ = contact angle of liquid at surface

2. How much energy does it take to clean tight spaces?

Δp = γ cosθ / R

planar

cylinder

NOTE: if θ is greater than 90˚, as with water on waxy surface, the force becomes negative or repulsive.

If surface is wetted, force pulls the fluid into the gap.

Relationship between gap size and capillary force for water on glass

Planar:

Cylinder:

2. Fluid Flow Theory – Small unfilled Gaps

Interfacial pressure difference at equilibrium

10

1

psi

0.1

0.01

0 20 40 60

Gap/diameter, mils

Surface effects in tight spaces retard fluid flow(computer model of flow in 50 micron gap)

Component

And that’s the easy stuff!

(Resistors, Capacitors, LCC’s, QFN’s)

Flux around 0603 Cap Flux under cap

3. Fully Filled Gaps are Much Harder

3 steps are required to remove a fully blocked gap:

1 Outer solvent depleted zone softened

2 Liquid jet with sufficient energy forms flow channels

3 Bulk residue is eroded & dissolved by fluid flow

Steps 2 & 3 require substantial Energy

3. Fluid Flow Theory – Filled Gaps

Research leading to PED

PED Works in a standard in-line configuration

Treatment system

21 3 4 5 6

Pre-Wash

Chemical Isolation

Rinse Final Rinsing

DryerWash

4. Inline Progressive Energy Dynamics Approach(PED)

New approach to design in-line cleaner

Involves a manifold design with increasing energy at each manifold

4. Inline Progressive Energy Dynamics Approach

Low Energy

Jet

Medium Energy

Jet

High Energy

Jet

Highest Energy

Jets

Pre-wash Wash 1 Wash 2 Wash 3

Heat & wet penetrate form flow erode surfaces outer layer channels flux

Wash section equipped with progressive energy dynamics

4. Inline Progressive Energy Dynamics Approach

SoftenOuterShell

CreateFlowChannels

ErodeFluxResidue

A Progressive Energy Design is:

A fluid delivery system Recognizes the 3-step process required to clean flux-filled

spaces Delivers only what is needed at each step:

4. Inline Progressive Energy Dynamics Approach

961 I/O “glass on glass” Flip Chip