ISE 370 Industrial Automation Instructor: Thomas Koon

1
ISE 370 Industrial Automation Instructor Thomas
Koon

• Camalot Dispensing System/Stencil Printer

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Introduction

• The main purpose of the discussion is to provide
  a basic understanding of the Camalot dispensing
  system and the stencil printer, and the
  electronic manufacturing processes and systems
  they support.

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Topics of Discussion

• Overview of the Electronic Manufacturing
  Processes.
• Stencil Printing
• Material Deposition
• Electronic Manufacturing Terms.

4
Electronic Manufacturing Process Brief History

• 1950-Present - Through Hole Technology.
• Axial
  lead Radial Lead Interconnect

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Electronic Manufacturing Process Brief History

• 1980-Present SMT (Surface Mount Technology)
• Passive Components Active Components
• Resistors Chip Carriers
• Capacitors Plastic
• Inductors Ceramic

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Through Hole vs. SMT

• Through Hole Features
• Lowest cost assembly technique
• 1 and 2 oz. Copper traces for high power
  applications
• Solvent or aqueous based cleaning systems

• SMT Features
• Up to 10 times size reduction over Through-Hole
  assembly
• Wide range of base materials available
• Improved signal to noise ratio when using
  ceramic base material

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Type III Assembly
Through hole on primary, SMT on secondary side of
PCB
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Wave Solder
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Surface Mount Assembly
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Print
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Visual Inspect
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Place
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Reflow
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Reflow Oven Diagram
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Standard Reflow Profile
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Classification of Reflow Technologies
Reflow oven types
TYPE A Vapor Phase (heated solvent) TYPE B Area
Conduction (hot air) TYPE C Hot Bar TYPE D IR,
Convection/IR and Convection Ovens TYPE E Laser
Reflow
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Nitrogen in Reflow
Nitrogen is used in reflow soldering to drive out
the oxygen from the soldering chamber. This
prevents the solder pads and component terminals
to oxidize during reflow of the solder paste.
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A Quick Review

1. What are the 2 basic types of PCB technologies?
2. What is at least one advantage of each type of
   technology?
3. How many of the 9 steps of a Type III PCB
   assembly process can you name?
4. What are the 2 types of components used in the
   manufacture of SMT PCBs?
5. What are some types of reflow ovens?

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Fluxes
The purpose of flux is to clean surfaces that
are going to be joined together to enhance
wetting by solder in the molten state.

• Major Flux Categories
• Rosin based (Pine Tree Sap)
• Organic Acid (Type OA). Water Soluble (the flux
  itself is not water soluble however the
  conductive residue left after soldering is).
• Low Residue No-clean flux. Leave on flux

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Flux Activity

• Flux Activity The ability of materials
  (activators) in the flux to remove corrosion and
  make the surface solderable .
• 3 Types of rosin flux
• R (rosin only)
• RMA (rosin mildly activated)
• RA (rosin activated)

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The Solder Processes
Solder is a fusible metal alloy, consisting
primarily of tin and lead, used for the purpose
of joining together two or more metals at a
temperature below their melting point.

• Two Major Processes
• Clean
• No-Clean
• (no-clean solder requires no-clean flux)

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Solder Paste Functions

• Solder paste has to perform several functions
• It needs to be printable
• It needs to transport flux and tin/lead to the
  joint
• It needs to coalesce during reflow to form a
  permanent and reliable electrical connection.

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Solder Paste

• Solder paste is a homogeneous combination of
  solder particles (ranging in diameter from about
  20 to 75 microns), flux, solvent, and a
  suspension agent.
• Solder (metal) particles (63Sn/37Pb)
• This combination of materials is known as the
  'vehicle system'. The vehicle system carries
  flux, solvent and thixotropic agents which are
  there to aid printing.

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Eutectic Solder
Eutectic solder is liquidous at 183C
(361F) Eutectic. An alloy with a lower melting
point lower than the melting points of its
components. 63 tin and 37 lead (63Sn/37Pb)
solder is referred to as eutectic solder.
Eutectics change directly from liquid to solid,
and the reverse, with no intermediate plastic
states
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Stencils

• Stencil Is a thin sheet of brass or stainless
  steel with openings that match the land pattern
  of the printed circuit board.
• Aperture Shape
• Square is Preferred Over Round
• for Better Paste Release
• Corners May be Rounded to
• Minimize Clogging
• Positive Taper with Bottom
• Opening 25 to 50 microns
• Larger than the Top

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Solder Alloy

• The alloy is formed to small particles with a
  diameter of 4 to 40 microns.
• For fine pitch printing, meaning lead pitch on
  0.5 mm and below, the particles are typically 20
  - 45 microns and for conventional printing 45 -
  75 microns. 

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A Quick Review?

1. What is the purpose of flux?
2. What are the 2 main components of solder? What
   temperature do the turn to a liquid state?
3. What are the 2 main soldering processes?
4. What is Fine Pitch ? (Size)
5. What is a stencil?

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Stencil Printer - Objectives

• Name and/or identify the main operating
  components of the Camalot solder paste printer
• Set-up and operate the solder paste printer in
  order to produce an acceptable electronic
  assembly (lab Exercise)
• State the material requirements, process
  controls, set-up procedures and troubleshooting
  techniques regarding the solder paste printer

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Stencil Printer Outline

• Machine Overview
• Squeegee Materials Selection
• Solder Paste Printing
• Set-up and Operation

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Stencil Printer Subassemblies

• Print Head
• Squeegee System
• Stencil/Screen Frame
• X,Y Table
• Vision System

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Squeege Materials

• Rubber
• Metal

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(Screen) Stencil Function

• Determines the pattern of solder paste
• Solder paste is placed directly on the stencil
  then squeegees force the paste through the
  opening

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Metal Squeege

• Work well with metal foil stencils
• Minimal scooping of paste from apertures
• Reduced print variability
• Reduced set-up time
• Reduced sensitivity to other printing variables
• Higher manufacturing yields
• Less Bleeding
• More expensive than rubber
• Easily damaged

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Rubber Squeege

• Work well with screen printing and stencils
• Compatible with non-wear resistant emulsions
• More compatible with rough inner layer presented
  by wire mesh
• Sensitive to other printing variables
• Can be specified at different hardness levels
• High durometer reading 70 recommended for stencil
  printing
• Easily worn out

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Rubber Squeege
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Metal Stencil Types

• Laser Cut Stainless Steel with Ni Plating
  Standard Pitch 0.8 to 1.0mm. Fine pitch 0.5mm or
  less
• Electroformed Co or Cr Hardened Ni Ultra-Fine
  pitch. lt 0.5mm
• Chem Etch 1.27mm pitch and greater

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Wire Mesh Screens

• Patterned by polymer emulsion
• Emulsion carries the pattern and the mesh holds
  it together
• Generally woven from stainless steel, polyester
  or nylon
• Diameter of wire and size of opening in terms of
  mesh number
• 100 mesh screen has 100 openings per liner inch
• (mesh/inch) are varied depending on process
  requirements
• Screen is attached to an aluminum screen frame
• Limited to 50 mil pitch aperture range

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Wire Mesh Advantages

• Low cost
• Fast turnaround
• Better surface conformance
• Good gasket properties
• Works well for prototype runs

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Wire Mesh Disadvantages

• Easy to wear out
• Higher squeegee wear
• Potential clogging
• Longer set-up time
• More cleaning and maintenance
• Susceptible to temperature

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Metal Foil Stencils

• Apply solder paste in finer patterns
• Usually made of stainless steel
• Strong base with excellent stability
• Thickness from 0.004 to 0.008
• Aperture size is determined by component pitch
• Hundreds of openings can be etched through the
  foil with accuracy to /- 0.002 (laser cut to
  /- 0.0004)
• Paste flows freely and uniformly

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Foil Stencil Advantages

• Complete open area
• Low squeegee wear
• Better print geometry
• Easy cleaning and maintenance
• Easy set-up

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Foil Stencil Disadvantages

• High manufacturing cost
• Less gasket properties
• Etch Factor
• Need good bonding at metal mask and flexible mesh
  border

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A Quick Review?

1. Name the main operating components of the Camalot
   solder paste printer?
2. What are the 2 main types of Squeeges?
3. What is the primary function of the Camalot
   Stencil Printer?
4. What are the 3 main metal stencil manufacturing
   processes?

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Set-up Operation

• Printed wiring board registration
• Squeegee pressure
• Squeegee (print) speeds
• Print stroke
• Print gap (on/off contact)
• Snap-off
• Printing modes

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Liquid Dispensing System Objectives

• Name and/or identify the main operating
  components of the Camalot liquid dispensing
  system
• Set-up and operate the dispensing system
• in order to produce an acceptable electronic
  assembly
• State the material requirements, process
  controls, set-up procedures and troubleshooting
  techniques regarding the dispensing system

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Dispensing System Outline

• Machine Overview
• Solder Paste Adhesive Selection
• Set-up and Operation

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Dispensing System Subassemblies

• X,Y,and Z Axis Gantry
• Dispensing Assembly
• Vision System
• Work board Holder

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Dispensing Materials

• Adhesives
• Solder Paste

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Adhesives

• 2 Main Adhesives Types
• Thermosetting -Two-part epoxies - (typically
  thermally cured)
• Acrylic Silicones- (UV cure, Thermal cure, or
  both)
• Properties
• Electrically Conductive or Insulating
• Thermally Conductive or Insulating

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Fluid Characteristics for Conductive Adhesives
- Thixotropic (more fluid when stressed) -
Viscosity ranging from 5,000 cps to 100,000 cps -
Stringy (drawing out a long tail when pulling
the needle away from dispensed fluid). -
Viscosity sensitivity to temperature (except for
silicones). - Sensitivity to moisture.
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Conductive Adhesive
Anisotropic Adhesive An adhesive with a low
concentration of metal particles to permit
conduction in the z-axis only
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Solder Paste Review
Solder pastes function is basically to supply
solder material to the soldering spot, hold the
components in place prior to soldering, clean the
solder lands and component leads and finally to
prevent further oxidation of the solder lands.
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Pumps(End Effectors)
Time/Pressure Auger Piston
(Air Pressure) (Archimedes)
(Positive Displacement)
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Archimedes Metering Valve (AMV)
Camalot uses this type of metering valve
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Dot Dispensing Sequence
Increasing retract speed can have drawbacks
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Choice of Needle
For Camalot 670 680 Rotary Displacement Pumps
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A Quick Review?

• Name the main components of the Camalot Liquid
  Dispensing System?
• What are the 2 main liquids dispensed?
• What type of fluid metering pump does the Camalot
  machine use?
• What is the function of solder paste?

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ANSI/IPC-A-610 RevB

• Standards
• IPC is a United States-based trade association
  that everyone follows!

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Alloy Temperature Chart
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Soldering Considerations
Solder Type
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Selector Guide
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Wire Bonding
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Type I Assembly
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Type I Assembly
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Type II Assembly
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Type II Assembly
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Type IIc Assembly
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Type III Assembly