1. High Performance Printed
Circuit Boards
By Joseph Y. Lee
Samsung Electro-Mechanics

2. Chapter - 7
Soldering and Cleaning of
High Performance Circuit
Board Assemblies

3. Introduction to Requirements
 Industry standardization
 Low cost method to bump die
 Cost-competitive substrates
 High yield assembly process

4. Two basic types of low melt flip-
chip interconnections
63/37 Low melt
97/3 High melt
chip chip
laminate laminate
Conventional Pb-rich Eutectic Sn-Pb

5. Problems
 Reliability is problem for bigger dies.
 Failure modes are either
delamination of encapsulant, most
often at the die passivation
interface, or chip cracking.
 Or combination of both delamination
or chip cracking.

6. Definition of a solder
 A solder alloy consists of two or more
elements that can wet to a surface,
most often copper, and then react to
form an adhesion layer, and, upon
solidification of the alloy, produces an
interconnection that has good
mechanical properties.

7. Phase diagram on binary solder alloys
L
e u a ep m T
e
Eutectic
temperature, Te, Proeutectic phase
the alloy is a
Te
r t r
homogeneous a β
liquid consisting of
A and B atoms.
A XA Xe XB B
Composition

8. 3 Solder Interconnections
Pin-in-hole Gull-wing-leaded
Ball-grid array

9. No-lead solder alloys
 Sn-Ag-Bi
 Sn-Ag-In
 Sn-Ag-Bi-In
 Sn0.965Ag0.035 – melts at 221°C
Environmental concerns to eliminate Pb.
Cost too high though.
No government pressure.
Pb use is not high compared to industrial paint and batteries

10. Flux
 Flux; when it is applied to surfaces that are
to be joined by soldering; flux cleans the
surfaces and results in a better bond
 Helps transfer heat.
 Prevents oxidation.
 Oxidation prevents any flow of molten
solder and prevents wetting.

11. Description of solder pastes
 It is a homogeneous mixtures of solder
powder, flux, and a vehicle.
 Must be able to withstand prolonged open
exposure to temperature and humidity without
undergoing changes that degrade its
performance.
 Must be able to withstand long delays or
pauses in the process and resume printing
with the print quality being equal to that
before the pause.

12. Solder paste printing considerations
 Squeegee  Screening equipment
 Blade material
 Stencil screen size
 Blade hardness
 pattern
 Blade configuration
 Solder paste
 Squeegee speed
 Paste rheology
 Metal content
 Down stop pressure  Alloy composition
 Substrate  Paste stability
 Material type  Paste tackiness
 Flatness  Compatibility with
 Size screen squeegee

13. Types of solder pastes
 No clean chemistries – consist of either
rosin- or resin-based flux system with a
suitable vehicle system.
 Water soluble fluxes – contain organic
or inorganic acids in the flux.

14. Key factors for solder paste
performance
 Equipment and setup parameters
 Stencil fabrication method
 Pitch of components
 Lead density of components
 Operator skills
 Component and card solderability
 Temperature and humidity

15. Characterize solder pastes
 Solder ball testing – solder paste on ceramic
substrate
 Residue – amount of clarity of the remaining flux
after reflow
 Solder paste wetting – hot air soldered leaded
(HASL) surface is more difficult to differentiate
 Slump – ability of paste to stay well defined after
screening
 Tack – certain amount of adhesive strength to hold
the component in place prior to reflow operation
 Worklife – how long the paste can remain on the
stencil before it can no longer print adequately

16. Conductive adhesives – 2 types
 Anisotropic – conductive in only one
direction
 Isotropic – conducting in all 3
directions
 Materials development of the conductive
adhesives
 Assembly process development
 Development of equipment set to form
reliable flip-chip attach interconnections.

17. Materials development
Polymer metal solvent paste
 Thermoplastic binder
 Conductive silver particles
 Solvent

18. Assembly processes
 First-level assembly – flip-chip attach
 Second-level assembly – BGA
modules
 Ceramic ball-grid array
 Ceramic column-grid array
 Plastic ball-grid array
 Tape ball-grid array

19. Post assembly cleaning
 Incoming hardware must be clean
and highly solderable.
 Flux residue and other
contaminations must be removed.
 Post assembly cleaning is required.
 Post assembly cleaning eliminates
a lot of unknowns in the soldering
process.

20. Chapter – 8
Environmentally
Conscious Printed
Circuit Board Materials
and Processes

21. Environmental survey
 Low water usage and sewer costs have high adjusted
production-based flow rates.
 Common pollutants: Cu, Pb, Ni, Ag and total toxic
organics (TTO).
 Two basic wastewater treatment configurations:
conventional metals precipitation and ion exchange
systems.
 ½ of survey have a formal pollution prevention.
 Water is wasted by unnecessary flow rates in their
rinse tanks.
 ¾ of survey implemented recycling, recovery, and bath
maintenance.
 Off-site recycling is commonly used.

22. Problems to POT (publicly
owned treatment)
 Pollutants that create fire or explosive
hazard.
 That cause corrosive structure damage.
 That will obstruct the flow in the POTW.
 Biological oxygen demand, released at
a flow rate or concentration.
 Materials hot enough to cause POTW to
exceed 104°F.

23. Pollutions Limitations in US
Geographical Federal Federal Federal State AQMD's
Area Destination “Serious” “Severe” “Extreme” California
VOC Emissions
to be major 50 tons/year 25 tons/year 10 tons/year 1 lb/day
VOC – Volatile Organic Compounds
AQMD’s – Air Quality Management District

24. Pollution Prevention
 It is defined as the prevention of the generation
of pollutants by minimizing or eliminating the
steps or materials that produce them.
 Circuit boards require a lot of water. Reduction
of water use is one goal for pollution
prevention.
 5lb (12kg) laptop represent about 40,000lb of
materials, resources, and wastes.
 Few PWB manufacturers use ozone depleting
substances in their products and process.

25. Things to Consider
 You do not need so much water.
 Determine the sources of waste.
 Ask employees to provide pollution
prevention solutions.
 Environmental management system –
requires documentation.
 Know costs of waste and pollution

26. 감사합니다