EAT – E-learning
Electronics Assembling Technology
E-learning Program
1. Introduction:
The electronics assembly process flow
Department of Electronics Technology
Budapest University of Technology and Economics
BME-ETT Elect2eat Team:
www.ett.bme.hu
Zsolt Illyefalvi-Vitéz, PhD
Olivér Krammer
János Pinkola, dr
et al
1
Chapters
1. Introduction: The electronics assembly process flow
Components and Printed Circuit Boards
2. Components used for electronics assembly
3. Printed wiring boards
4. Surface finishes used on printed wiring boards
Assembling Technologies
5. Soldering techniques and solder joint design principles
6. Solder paste stencil printing
7. Component placement methods and process sequences
8. Reflow soldering, reflow ovens and temperature profiling
9. Wave soldering and thermal profiles
10. Selective soldering
11. Hand soldering and assembly repair
Inspection, Test and Quality Management
12. In-line inspection and test techniques
13. In-circuit and functional test
14. Total Quality Management
2
Electronics assembly variations –
Through-Hole Technology (THT)
Electronics Assembly is the process of attaching component leads or
terminations to lands or pads of conductors on a circuit board and then join
them by soldering.
There are two primary categories of components and assemblies; through
hole and surface mount.
At through-hole technology
(THT), component leads are
inserted through holes in the
printed wiring board (PWB);
and soldered to the lands on
its other side.
A TH component is the DIL IC
(dual-in-line integrated circuit),
whose leads usually have a
pitch of 2,54 mm (0,1”)
3
SMT – Surface Mounting Technology
Terminations of surface mount
devices (SMDs) are attached to
the board pads by soldering to
make both electrical and
mechanical connections.
In some cases conductive
adhesive joints are used.
Process steps:
1. Solder paste application
2. Adhesive application for wave soldering
3. Components placement
4. Adhesive curing by heat or UV light
5. Reflow or Wave Soldering
6. Board cleaning
4
Electronics assembly combinations
5
The assembly line for reflow soldering
6
Types of discrete components by function and assembling
Active components: amplify the
electric signal, need energy source,
built from semiconductor materials
Passive components: amplify the
electric signal, do not need energy
source, built on insulating materials
Assembling types of components:
Through Hole components
7
Surface Mount passive components and integrated circuits
Thick film chip resistor
SOIC:
Small Outline Integrated Circuit
Multilayer ceramic capacitor
PLCC:
QFP:
Plastic Leaded Chip Carrier
Quad Flat Pack
8
Surface Mount ICs with high lead count
QFP (Quad Flat Pack)
Very high number of leads
(up to 1000) are located
at all the four sides of the
package
Pitch minimum is 0,3 mm
FC–PBGA (Flip Chip – Plastic Ball Grid Array
9
Substrates: Types of Printed Wiring Boards
In an electronic assembly the substrate or circuit board supports the
components mechanically, and interconnects their terminations electrically.
Printed wiring board is the general term for completely processed printed
wiring configurations, including single-sided, double-sided and multilayer
boards with rigid, flexible and rigid-flex base materials.
For circuit cards and modules the rigid printed wiring boards are used, while
flexible and rigid-flex printed wirings are popular for the interconnection of
cards placed in different position in equipment or of different units.
Rigid printed wiring board
Flexible printed wiring board
10
Printed Wiring Boards
Printed wiring board (PWB) is a substrate, which is made up of an insulating
board with copper foil tracks on it. The components are fixed to the PWB and
connected to the conductive copper tracks by soldering. In general, the base
material of a PWB is a copper clad laminate, and the conductive pattern is
prepared from the copper foil by subtractive technology, that is by the
combination of photolithography and chemical etching. Multilayer boards are
made by the lamination of single boards and adhesive layers. The patterns of
the different layers are connected with plated holes (or vias).
11
Assembling process steps defined by soldering
12
Mixed assembly, applying glue:
combinations of reflow and wave soldering
13
Soldering
Solder joints use some metal alloy material to fasten and electrically
contact conductive parts, like soldering pads and component leads. Applying
heat and some flux, the surfaces of the parts are wetted by the melted alloy,
and the joint is formed when the solder re-solidifies.
The soldering alloy has a – preferable eutectic – melting point (MP), lower
than to injure the parts. Most popular alloys are:
• lead-free SAC alloy, e.g.: 95.5Sn3.8Ag0.7Cu; MP = 217 oC
• conventional leaded alloy: 63% Sn 37% Pb; MP = 183 oC
The flux helps the wetting process. Flux types are as follows:
• Resin (most popular): non-corrosive, soluble in alcohol, needs cleaning
• RMA = Rosin Mildly Activated: resin or rosin activated by acid
• no-clean flux: transparent, insulating, no need for cleaning
• water soluble organics.
Two types of soldering are in use in mass production, namely:
• reflow soldering when the solder is applied in paste form and then melted
(reflowed) to make the joints;
• wave soldering, where the solder and heat source is a solder wave.
14
Solder paste application
Solder pastes are formulated to be printable mixtures, and they are applied to
the pads of the board using stencil printing.
15
Placement of SM components for reflow soldering
Surface mount assembly consists of three basic processes:
• solder paste application,
• component placement, and
• reflow soldering.
16
SMT pick-and-place head and machine
Placement to optically recognized pad positions.
Polarity checking and simple measurements
during placement.
Efficiency up to 60.000 SMD / hour.
17
Component placement failures inspected optically
- Component falls down from the nozzle
- Misplacement and rotational offset (see figures)
- Wrong polarity
- Billboard (component lays on the edge)
- Face down component
- Component placed on another component
- Injured component
18
Reflow soldering
Reflow soldering is
usually carried out in
• a convection type or
• a combined IR heated
hot-air (or N2) furnace.
Conveyor belt type
ovens are applied in
both cases.
19
Wave Soldering: automated soldering of
through-hole and surface mounted assemblies
-shaped wave
(oxide-free)
foamed or
sprayed flux
pump
pump
Flux
application
Pre-heating
80…120 ºC
Solder wave
240…260 ºC
PWB-s are transported through the wave soldering equipment by
a conveyor belt, which has a transport speed of: 1,3..1,5 m/min).
Both the heat and the solder are provided by the solder wave.
20
Integrated Repair Station
Repair stations are used to correct and repair
recognized soldering failures, with functions
as follows:
Visualization
of soldering
failures
Integrated
shuttle
Marking of
component
positions
Pictures of
the originally
detected
failures
Storage of
error pictures
Reporting of
failure class
21
Fabrication of the LEADOUT board
by lead-free soldering – an example
In the following slides some details of the fabrication of the
LEADOUT demonstrator board is presented.
1. Equipment and data of assembly with photos
- stencil printing & stencil design
- assembly – component placement
- reflow soldering
2. Fabrication problems and their effects
- offset of stencil aperture
- solder paste misprint
- imperfect component placement
- paste misprint and smearing
22
Stencil Printing & Stencil Design
Thieme TES/S-25 stencil printer features:
Printing speed: 20…140 mm/s
Pressure: 10…60 N, angle: 45…90º
Settings during experiment:
Printing speed: 400 mm/s
Pressure: 55 N, angle: 45 º
Stencil:
Laser-cut
150 µm thick
Stainless steel
Inverse home plate apertures
for Surface Mount Components
23
LEADOUT ”lead-free” demonstrator after stencil printing
24
Assembly – Component Placement
TWS laser quadra features:
Automatic pick & place
2 nozzles
Laser centering
0402 smallest component
0,4 mm smallest pitch size
Testboard
used to determine proper
parameters for component
placement and soldering
25
The LEADOUT demonstrator after component placement
26
Reflow Soldering
ESSEMTECH R006 reflow oven:
Convection with infra heating
Nitrogen atmosphere can be used
Settings:
Preheat: 190 °C
(in air)
Soak: 200 °C, 160 s
Reflow: 220 °C, 20 s
Green: 3x3 cm copper area
Red: 0603 chip R Blue: air
27
The LEADOUT demonstrator after reflow soldering
28
Monitoring the Assembling – Process Examples
Effect of solder paste misprint:
wetting corrected misprinting
After stencil printing
After reflow soldering
29
Monitoring the Assembling – Process Examples
Effect of the offset of stencil aperture:
wetting pulled back the solder and the SMD
After stencil printing
After reflow soldering
30
Monitoring the Assembling – Process Examples
Imperfect component placement #1:
reflow and wetting pulled back the SMD
After component placement
After reflow soldering
31
Monitoring the Assembling – Process Examples
Imperfect component placement #2:
reflow and wetting pulled back the SMD
After component placement
After reflow soldering
32
Monitoring the Assembling – Process Examples
Imperfect component placement #3:
reflow and wetting pulled back the SMD
After component placement
After reflow soldering
33
Monitoring the Assembling – Process Examples
Paste misprint and smearing:
resulted in solder ball formation
After component placement
After reflow soldering
34
Monitoring the Assembling – Process Examples
Paste misprint and smearing:
resulted in solder bead formation
After component placement
After reflow soldering
35