HUMAN

1
WHAT IS SMT?

Surface Mount Technology means the technique of affixing the Surface MountComponents automatically to the surface of PCB (Printed Circuit Board).

The component used in SMT is called as Surface Mount Devices (SMD).

These components are leadless having soldering terminals at the corner of chip orhaving solder balls (BGA) or flat surface IC’s.

(a) AI (Auto Insert) (b) SMTFigure 1.1

Figure 1.2 Basic SMT Line

Why SMT is needed?

For the mass production of electronic circuit boards requires some technique to reduce themanufacturing cost & time. In Through Hole Technique the leads need to be inserted intoboard and hence the problems were automatically encountered if the leads are not fittedproperly, which slows down production rate.

All electronic products require more function & small size, so circuit PCB needs to becompact. The leads that have used for connection actually not require for printed circuitboard construction. The component can be soldered directly on to the pads of the PCB,

which saves the cost of making holes in printed circuit board.

As the components were mounted on the surface of the board rather than havingconnections that went through the holes in the board, the technique is called as SurfaceMount Technology or SMT & the devices used in this is called Surface Mount Devices orSMD.

Definition of SMT

“Surface Mount Technology (SMT) is a method for constructing electronic circuits inwhich the components (SMD – Surface Mounted Device) are mounted directly onto thesurface of printed circuit boards (PCBs)”. Electronic devices made with this method arecalled surface mount devices or SMDs.

2
GROWTH IN HISTORY FOR SMT

HISTORY:

Surface mount technology started in 1950’s when surface mount components were appliedfor the first time to military supplies. In 1960’s the surface mount technology grew out oflimited hybrid circuit products market and attached with ceramic to the surface ofmaterial.

In 1970’s Japanese electronics industry produces small portable electronic productswith which the production costs could be reduced and to which consumers preferred. Asonly the solder joints hold the component to the board, the surface mounted devices(SMDs) are usually made small size & light weight. SMDs can be one-quarter to one-tenthof the size and weight, and one-half to one-quarter of the cost of equivalent through-holeparts.

The size of Chip components reduces from

3216 –> 2012 –> 1608 –> 1005 –> 0603 –> 0402

The IC’s became more compact from

SOP –> SOJ –> QFP –> FCC –> BGA –> Flip Chip

In the early 1980’s, the level of integration of the integrated circuit(IC) was even higherand the electronic circuits became complicated. With this change the number of leadsgreatly increased and in many cases was more than 100. Since DIP IC for insertionrequired more area than the IC for surface mount which has no leads, its demand started todecrease. Until the mid-1980s, surface mount components had been used mainly for smallhybrid circuits. The reason for that was the lack of high-speed automatic equipment whichcould bring about mass production of products. In recent years, due to the development ofthe surface mount related technologies, diverse components of surface mount are massproduced and the high-speed equipment by which a variety of micro-parts can be appliedto dense substrates is developed so that the surface mount products are enable to produceat a lower cost than their own company’s existing product.

Figure 2.1 Transition of Mounting types

Transition of Mounting Types:

(1) 1950-tube, the first generation, large high-voltage devices.

(2) 1960- The second generation, mobile products parts.

(3) 1970- The third-generation small mobile devices, odd-shaped parts.

(4) 1980- The fourth generation, compact high-density devices, surface mount parts.

(5) 1990- The fifth-generation ultra-compact-high-density devices, complex surface-mount components, ultra-miniaturization, thinned, multiplexed, high-density mounting,high-speed mounting.

Advantage of SMT:

The main advantages of SMT over the through-hole technique are:

• Sophisticated manufacturing processes.
• Small size and light weight components are used.
• No need to drill the holes through board.
• Simpler automated assembly.
• Component placement errors are corrected automatically.
• Both sides mounting are possible.
• SMT parts generally cost less than through-hole parts.

Disadvantage of SMT:

• High initial cost and time of setting up for production.
• Difficulty in manual handling due to the very small sizes.
• As solder paste is used it makes repair of devices extremely difficult, and oftenuneconomical.

Ask YourselfWhat is the basic of SMT?How much do you know about basics of SMT?

3
INTRODUCTION TO SMT

3.1 Introduction to SMT Machines

1) Loader / Un-loader

Loader and un-loader is used for loading and unloading the PCB’s, an arriving PCB istaken up and taken down by the attached conveyor and push into the magazine by pusher.The magazine is indexes to the next position and is ready for the following loading andunloading cycle.

Before starting the line, the set pitch difference of loader and Un-loader is to be checkedalways.

Figure 3.1 Magazine loader

Figure 3.2 Vacuum loader

Figure 3.3 Gate Conveyer

Figure 3.4 Magazine Un-loader

2) Screen Printer:

Screen printing is a printing technique which is used to print solder paste or adhesive onthe PCB surface. The stencil has open areas to transfer the solder paste. A roller orsqueegee is moved across the stencil, forcing solder past through the mesh on PCB.

Screen printing is very important because it is closely related with production quality.80-90% of the defects in the product are caused by inappropriate screen printing.

Figure 3.5 Screen Printer

3) Solder Paste Inspector (SPI):

It is the equipment in the SMT line to detect faults occurred during solder paste printingprocess. The inspection criteria are set by the program. It is automated equipment;developed to reduce the errors due to visual human inspection. In production line wheresmall pitch components are used, SPI is essential as 80% of SMT defects depend uponpaste printing. It is used for detecting printing defects like missing solder, excess solder,no solder, solder paste height, etc.

In-line SPI is used for 100% detection purpose whereas Off-line SPI can be used onlyfor sampling check.

Off Line

In Line

Figure 3.6 SPI

4) Mounter:

The components to be placed on the boards are usually delivered to the production line ineither paper/plastic tapes wound on reels or plastic tubes. Some large integrated circuitsare delivered in static-free trays. The pick-and-place machines (Mounter) remove the partsfrom the tapes, tubes or trays and place them on the PCB.

Machine is used for standard part mounting and dissimilar part mounting dependingupon the requirement.

(Standard component like resistors, capacitors & dissimilar component like IC, BGA,and Connectors, etc.)

Types of Mounter:

(1) One by One Mount (Gantry Type):

It is low speed production equipment. When PCB moves in the loading area, the PCBstays in fixed position and the head of mounter moves along X and Y axis, pickups andloads components on PCB for small number of points in production line and for mountingof LCD and RF modules on PCB of mobile phone. One by one type is a suitable chipmounter, in case of higher number of points in production line, rotary chip mounter is themain mounter and then multi-mounter is used.

Figure 3.7 One by One Mount (Gantry Type)

(2) Rotary Mount:

It is used in less complex and mass production system. It is a loading system where thePCB moves to the mounting position; the fixed head drum rotates and repeats the motionand the table with loaded PCB moves along X, Y axis. It is suitable for high mountingpoints per PCB, since more than 200 points space between parts is narrow. It is used inhigh density production type mountings.

The area occupied by equipment is high and the loading area is too wide, length of theline gets longer, and the weight of main body is so heavy that various problems occur suchas vibration from 2nd and 3rd floors, generally it is installed in the 1st floor constructionwith reinforcements.

Figure 3.8 Rotary Mount

(3) Module Mount:

In the modular type equipment, the speed of each module is not fast, depending on theadded quantity of the module the production capacity increases, and it has advantage inacquiring a smaller area and the lighter weight of equipment than rotary type. Foroptimizing the loading program, the supply of required components needs to be workedseparately through many feeders so that it guarantees maximum efficiency as the quantityof production requirement gets higher.

Therefore, the quantity in supplying of components by manufacturer to multiplenumbers of reel units should be efficiently managed. Otherwise, if a bottleneck occurs in

the supply of component, in case of higher number of component requirement in loadingmodules, it will be lead to a reverse effect and the production capacity of the whole linegets lower.

Figure 3.9 Module Mount Equipment

(4) Reflow Oven:

It is the equipment used to harden the solder paste and make the bonding between chips,solder paste and PCB pad.

The PCB first enters in a pre-heat zone, where the temperature of the board and all thecomponents are gradually, uniformly raised. The boards then enter a zone where thetemperature is high enough to melt the solder particles in the solder paste, bonding thecomponent to the pads on the circuit board.

Figure 3.10 Reflow Oven

Types of Reflow:

(1) Vapor Phase Reflow

It was developed by Western Electric in 1975,in this soldering type a high temperature isused to vaporize chemical which is blown on the PCB to set the solder paste.

(2) IR Reflow (Infrared Reflow)

It is a type of soldering which uses heat generated by radiation from quartz filament byapplied voltage.

(3) Laser Reflow

It is a type of soldering which uses laser beam. There are two types, CO2 laser and YAGlaser.

(4) Heat Air Reflow (Convection Reflow)

It is a soldering type that uses heat generated by the fan heater to heat the air in a certainarea by convection, maintaining uniform temperature.

(5) Type of Reflow in N2 (Nitrogen) Atmosphere

All materials of the general atmosphere generate oxide by reaction with oxygen andespecially in high-temperature speed of oxidation are faster. However, chemical change isless in the presence of Nitrogen; it could be controlled for lead soldering in nitrogenatmosphere .The above type is nitrogen atmosphere reflow. In 2006, there is a change inprocess from existing lead solder paste to lead-free (Pb-free) solder paste. From thebeginning of 2000 N2 (nitrogen) atmosphere reflow equipment has been developed as asubstitute for Pb-free solder type.

(6) Automated Optical Inspector (AOI):

It is the equipment in the SMT line to detect external faults in production based on theinspection criteria set by the program. Automated equipments were developed and used tostabilize the quality of standardized tests by compensating for errors existing in visualhuman inspection, caused by manual factors, ability of inspection per person andinstability in inspection quality by changing workers.

There are off-line (desk style) type and in-line type of test equipment and generally in–line type is more expensive than off-line as it has many more options.

Figure 3.11 AOI

3.2 SMT Line Configuration 1) Bond +AI Line:

Glue is used to hold the components to the PCB during the total process.

Process Flow:

Apply glue by printing through stencil or dispensingthrough syringe method.

Do the Mounting of SMT components.

Cure the adhesive in reflow. (Glue)

Manually insert the through-hole (TH) componentson other side of PCB.

Pass to the wave soldering m/c for soldering of TH &Passive SMT Components.

Figure 3.12 Bond + AI line Process Flow

Line Configuration:

Figure 3.13 Bond + AI Line Configuration

2) SMT + AI + Bond Line:

In this process first need to do solder printing then Bond process because bond require lesscuring temperature (150C) than solder paste.

Process Flow:

Do the solder paste printing at side-1 of PCB.

Place the SMT components through mounter.

Do Soldering by reflow oven.Insert auto & Manual through hole components onside-1.Reverse the PCB; apply Adhesive to the side-2 ofPCB.Do the Mounting of SMT Passive components.

Cure the adhesive. (Glue)

Reverse the PCB on side-1 and pass through wavesolder for soldering of TH & Passive SMT

Components.Figure 3.14 SMT + AI +Bond line Process Flo

Line configuration:

Figure 3.15 SMT + AI +Bond Line Configuration

3) SMT + SMT Line:Process Flow:

Do the solder paste printing on side-1 of PCB.Place the SMT components through mounter.

Do Soldering by reflow oven.

Reverse the board & do the solder paste printingon side-2 of PCB.

Place the SMT components on side-2

Do Soldering by reflow oven.

Figure 3.16 SMT + SMT line Process FloLine configuration:Top side:

Figure 3.17 SMT + SMT Line Configuration

Bottom side: Reverse the PCB to do mounting on other side and repeat the process as

above.

4
BASICS OF SMT TRAINING

Introduction to SMT Material:

The component used in Surface Mount Technology is called as Surface Mount Device orSMD. An SMT component is usually smaller than its through-hole counterpart because ithas either smaller lead or no lead at all. It may have short pins or leads of various styles,flat contacts, and a matrix of solder balls (BGAs), or terminals on the body of thecomponent.

Component NameAI ComponentsSMT Components

Resistor
Capacitor
Diode
Transistors
IC

Figure 4.1 AI and SMT Components

Packages:

Surface-mount components are usually smaller than through hole and are designed to behandled by machines rather than by humans. The electronics industry has standardizedpackage shapes and sizes.

Figure 4.2

Component Spool/reel:

Figure 4.3

Spool Label:

Figure 4.4

Types of Spool:

Figure 4.5
IC Tray Supply Type:
Strip	Tray	Spool/Reel

Figure 4.6

4.1 R-L-C Value Calculation 1) Resistor:

It is used in the electronic production, it decides amount of the electric current and itshould be used according to volume (or capacity), size & tolerance.

SMD resistors are marked with their resistance values using three digits, two significantdigits and a multiplier digit. Commonly white lettering on a black background is used.

Usually the black or coloured coating is done only on one face of the device, while thesides and other face are white ceramic or uncoated. The coated surface with the markingon it is normally positioned facing up when the device is soldered to the PCB.

Mark : ‘R’

Symbol : Unit : ‘Ω’ – Ohm

Figure 4.7Way of Reading:

The basic resistor is marked with the number of three (3) figures in the level of J (5%).Initial two (2) figures mark index and one figure marks multiplier.The details (or Precise) resistor level F (1%) is marked with the number of four (4)figures and initial three (3) figures mark index and one figure marks multiplier.The unit of resistor is marked as Ohm (Ω). The unit can be converted as follows –1 Ω = 1 X 10^° Ω = 1 Ω (1 ohm)1kΩ =1 X 10³ Ω = 1,000 Ω (1 kilo ohm)1MΩ =1 X 10⁶ Ω = 1,000,000 Ω (1 Mega ohm)

Allowable Tolerance of Resistor Chip

MarkAllowable ToleranceNote

J5%General Chip Material

F	1%	Detail (or Precise) chip material
		Figure 4.8
Example:

The 3 digit part number indicates ±5% tolerance (J Type).R413

R100 = 10 Ω ±5%R101 = 100 Ω ±5%R102 = 10 X 100 = 1000 Ω= 1K Ω ±5%R103 = 10 X 1000 = 10 k Ω ±5%R0R5 = 0.5 Ω (R between the 2 digit denotes a decimal point.)The 4 digit part number indicates ±1% tolerance (F Type).R4102

R1001 = 100 X 10= 1 kΩ ±1%R1003 = 100 X 1000 = 100 kΩ ±1%R1004 = 100 X 10,000 =1000 kΩ = 1MΩ ±1%

2) Capacitor:

A capacitor is a device which stores and discharges electric current, depending on thecapacity, size, character and tolerance of a dielectric which is placed in between twoconducting plates which create the capacitance.

Non electrolytic capacitors are usually unmarked and to determining their value need toremove it from the circuit and measure it with a capacitance meter (LCR meter).

SMD (non electrolytic) capacitors exhibit the same body colour on all four facescovered by the end caps.

Mark : ‘C’ Symbol : Unit : ‘F’ Farad.

Figure 4.9How to Read Capacitor Code:A condenser can be marked with a 3 digit number, where the first two are the 1st and 2ndsignificant digits and the 3rd is a multiplier code. Unit of condenser is Farad (F) – basicunit can be marked as pico-farad (pF)

The unit can be converted as follows –1mF = 10^-6 (micro Farad)1nF = 10^-9 (nano Farad)1pF = 10^-12 (pico Farad)Condenser Tolerance:

MarkAllowable ToleranceNote

±0.25%5pF ~ 10pF applied values

D±0.5%5pF ~ 10pF applied values

J±5%10pF or higher applied values

K ±10%

M ±20%

Z – 0.25% ~ + 80%

Figure 4.10Example:

C 100 = 10pFC 101 = 100pFC 102 = 1000pF = 1000 x 10^-12 = 1 x 10^-9 =1nFC 103 = 10000pF = 10000 x 10^-12 = 10 X 10^-9 = 10nFC 104 = 100000pF = 100000 x 10^-12 = 100 X 10^-9 = 100nF = 0.1 μF

C 105 = 1000000pF = 1000000 x 10^-12 = 1 X 10^-6 = 1.0 μF

C 0R5 = 0.5pF

The R in between the digits denotes a decimal point.

Following methods are used to increase the capacity of a capacitor

1. Using wider conducting plates.

2. Decreasing the distance between the plates.

3. Using higher dielectric constant of the insulator.

Resistor & Capacitor Value Calculation Method:ResistorCapacitor

1 Ω = 100 Ω = 1 Ω (Ohm)1pF = 10^-12 (pico Farad)

1kΩ = 103 Ω =1,000Ω (Kilo ohm)1nF = 10^-9 (nano Farad)

1MΩ =106 Ω = 1,000,000Ω (Mega ohm)1μF = 10^-6 (micro Farad)

While calculating the values of capacitor, 1st calculate the value by resistor calculatingmethod and then convert it into capacitor value by using above converting method.

Example :

R 100 = 10ΩC 100 =10pF

R 101 = 100ΩC 101 =100pF

R 102 = 1kΩC 102 =1nF

R 103 = 10kΩC 103 =10nF

R 104 = 100kΩC 104 =100nF

R 105 = 1.0MΩC 105 =1μF3) Inductor:

Due to the small dimensions of SMDs, SMT inductors are available in limited values ofless than about 1mH. It is a metal conductor looped through a ferrite bead with end caps.They are of dark grey in colour. Larger inductors and transformers may be through-holemounted on the same board.

SMT inductors with larger inductance values often have turns of wire or flat straparound the body, allowing the wire or strap to be seen. Sometimes a ferrite core is alsopresent.

Same as a capacitors, component values and identification are not usually marked onthe component itself. It needs to be removed from the circuit to determining the values.Increasing the number of turns of wire in the coil will increase the value of inductor inHenry.Mark : ‘ L ‘Symbol : Unit : ‘H’ Henry

Figure 4.11 Inductors

How to read Inductor Code:

The unit of inductor is Henry and the basic unit is nano Henry (nH).1H = 10^-6 (micro Henry)1nH = 10^-9 (nano Henry)

Example:

L 471 = 47 10¹ 470nHL 4N7 = 4.7nHThe presence of N in the value of inductor coil denotes a decimal point.

4.2 Introduction to Other SMT Components 1) Diode:

Mark : ‘ D ‘Symbol : It’s a PN functional bipolar semiconductor device used in various circuits.Types of diodes are rectifier diode, zener diodes, light emitting diodes (LED) etc.

Figure 4.12

2) Transistor:

Mark : ‘Q’ OR ‘ TR ‘

Symbol : PNP Type

NPN Type

Transistor is a component which amplifies the current. Various kinds of analoguecircuits use transistor while less used in the digital circuit. The amplification characteristicof transistor makes no difference to the digital circuit which is handled by 2 signals being‘ON’ and ‘OFF’. The circuit function is mostly handled by the IC.

There are 2 types of transistor, PNP and NPN, depending on the placement of thesemiconductor components.

Figure 4.133) Integrated Circuit (IC’s):

Mark : ‘IC’ OR ‘U‘

Integrated circuit is a package of high density combination of transistors, resistors andcapacitors. IC is actually a high density printing technique of resistors, capacitors andtransistors on a silicon wafer performing the functions of transistors, resistors orcapacitors.

IC Polarity can be recognized by notch/ white colour band / dot marking on it.

For SOP – Pin to the side of the notch is considered as First Pin.

Figure 4.14

For QFP Pin to the side of notch in anti clockwise direction is considered as first pin.

Figure 4.15

Types of IC’s:

(1) SOP (Small Outline Package): The IC with leads coming outwards on two sides.

Figure 4.16

(2) SOJ (Small Outline Junction): The IC with leads going inwards on two sides.

Figure 4.17

(3) QFJ (PLCC) (Quad Flat J-Lead Package) or PLCC (Plastic Lead less Carry Package): The IC with leads going inwards on four sides.

Figure 4.18

(4) QFP (Quad Flat Package): The Quad Flat Package IC with leads coming outwards on four sides.

Figure 4.19

(5) BGA (Ball Grid Array): It is one of the large scale integrated circuit packages. LSI bare chip is mounted on the small quad printed circuit board. Behind the PCB, 2dimensional arrays of hemispherical terminal balls are arranged.

Figure 4.20

(6) CSP (Chip Size Package, Chip Scale Package): The semiconductor package has the same size as the chip or little bigger. Collectively it is an ultra small, ultra thin and lightweight semiconductor package.

Figure 4.21

(7) Flip Chip (flip chip): The semiconductor without leads is bonded directly on the PCB. The package size is same as the chip so it makes it smaller and lighter. The input/outputterminal is present on the chip base.

4) Filter:

It filters the capacity and frequency.

Figure 4.225) Connector:It connects different PCB or circuit.

Figure 4.23

4.3 SMT Defects 1) Missing Solder:

Cause: i) Solder not visible.ii) Solder paste not applied.

Figure 4.242) Short (Shorted Bridge):Cause: i) Terminals connected by extra solderii) The land between the terminals is filled with solder.

Figure 4.25

3) Missing Components:

Cause: i) The condition of the part is affixed in the wrong place.ii) Lost status of part on specific location.

Figure 4.264) Cold Lead Solder:Cause: Bad solder due to violation of correct temperature.

Figure 4.27

5) Less Solder:

Cause: Less than the stated temperature (stated temperature violation) leading to lesssolder.

Figure 4.286) Solder in Excess:Cause: i) More than the stated temperature leading to excess solder flow.ii) Excess supply of solder paste during paste printing.

Figure 4.297) Wrong Components:Cause: Affixing components other than what is prescribed for a designated area.

Figure 4.308) Reverse Placement:Cause: Components mounted with opposite polarity.

Figure 4.31

9) Upside Down Component Assembly:

Figure 4.32

10) Miss Alignment:

Cause: Change of the X or Y co-ordinates or axis.

Figure 4.33

11) Twisted:

Cause: The case of turning the component from its specific location while being mounted.

Figure 4.3412) Broken and Damaged Parts:Cause: The case of damaging components and peeling PCB.

Figure 4.35

13) Tombstone:

Cause: The case in which one side of the component gets raised and its electrode makesno contact with the PCB.

Figure 4.3614) Solder Balls:Cause: i) Due to improper stencil cleaning.ii) Due to wrong design of component pad on PCB.iii) Wrong setting of reflow temperature profile.

Figure 4.37

15) Floating:

Cause: The state in which all the leads of the IC are not connected to the PCB and one sideis raised and is floating on top of the PCB.

16) Scratches:

Cause: The state in which there are scratches on the PCB surface.

17) PCB Bending:

Cause: The case in which the PCB surface is not being flat and has bends.

18) Overheat:

Cause: In the event of occurring ripples and over heat in the reflow oven and damaging inthe components and the PCB.

4.4 Introduction to SMT Product Parts 1) PCB

The full form of PCB is Printed Circuit Board. It is used to build electronic devices.The components are place on PCB to make a circuit. It also provides the electricalconnection between the components.

It is a thin, non-conducting sheet of material. The most common material used is a glassfiber epoxy laminate material. A thin layer of copper is then chemically deposited on eachside of this material.

Then the connection diagram is “print” onto the PCB. The connection diagram is the

wiring required to connect the components. In early days these connections were donewith wires. This is the reason PCBs are also sometimes referred to as printed wiringboards (PWB). The “printing” is usually done by photographically transferring the imageto the board. This image is “printed” with an acid resistant material.

Then, the PCB is put into an acid bath. The acid removes the copper from the board,except for the areas protected by the resistant material. This process leaves the “printed”connections on the PCB. Finally, a protective coating is applied to the board to preventcorrosion of the copper traces.

The above process is for doubled sided or two layer PCB. By repeating the aboveprocess it is possible to make any number of layers PCB and laminating the resultingboards into a single PCB.

Figure 4.38

Types of Printed Circuit Boards:Single Sided BoardIt is a simple Printed Circuit Boards with only single layer. All electrical parts and

components are fixed on one side and copper traces are made on the other side.Double Sided BoardIt is a most common type of PCB in which parts and components are attached to both

sides. It has connecting traces on both sides.Multi Layered BoardMulti layered PCB consists of several layers of substrate separated by insulation. Most

common multilayer boards are: 4 layers, 6 layers, 8 layers and 10 layers. However, thetotal numbers of layers that can be manufactured are over 42 layers. These types of boardsare used in extremely complex electronic circuits.

Material used in PCB:

(1) Conductive ink

(2) Laminate materials

• BT-Epoxy
• Composite epoxy material, CEM-1,5
• Cyanate Ester
• FR-2
• FR-4, the most common PCB material.
• Polyimide
• PTFE, Poly tetra fluoro ethylene (Teflon)

PCB Guide Design Sample:

A lot of company’s R&D does not have standard of fiducial mark designing. R&D personsdo not have SMT manufacturing knowledge; they couldn’t consider SMT productionprocess. (Fiducial mark size, position and shape.)

Wrong PCB design- No standards are followed while designing.

Figure 4.39

Figure 4.40 is the sample of fiducial mark position of mobile PCB. The method willavoid the 180 reverse production. In mobile PCB usually used fiducial mark size is0.8mm to 1mm. If its size is bigger, the tolerance ratio also will increase.

Figure 4.40

2) UV Bond/ SMD Adhesive:

Bond is used to hold surface mounting devices in its position during the placementoperation.

• The bond (SMT Adhesive) needs to be conductive.
• It should have long shelf life.
• Small cure time.
• Moisture resistant.
• Non-corrosive.
• Free of holes & voids.

Storage Condition:

Glue shall be ideally stored in a refrigerator, dry location in unopened containers at atemperature between 1 to 10C.

IQC Procedure: Process Flow

Check the material Qty and its documents before receivingfrom store.Check the material for damage.Check the Mfg. & Expiry Dates.If not OK, return back to store.Check the contents with Quality report.Attach a detailed information tag.Store the bottles in refrigerator at 1 to 10C.

Figure 4.41Use Procedure:

Update the removing time in “In & Out Consumption Report”Keep the glue 2-3 hrs at room temp. Make different area of ‘FORAGING’ and ‘AFTER AGING’.Take the glue to use on-line from ‘AFTER AGING’ area only.

Figure 4.42Application Methods:

(a) Pin Transfer

It uses matrix of pins for transfer of glue, it is fast like stencil printing.

(b) Dispensing/ Syringing (Most widely used)

You can apply varying amount of glue depending upon the component.

Figure 4.43 Dot Format

Line Configuration

Figure 4.44

(c) Stencil printing

It is similar to paste printing, faster in operation.

Figure 4.45

Sometimes due to high height of component dispenser required with screen printer.

Line configuration

Figure 4.46Glue Curing Objectives:To make temporarily reliable mechanical connection between the printed circuit board andthe surface mounting devices without damaging the components and printed board.

Curing Temperature Profile

Figure 4.47

3) Solder Paste:

Solder paste (or solder cream) is used to connect the terminal of components to attachmentpoints (Pad/land) on a printed circuit board. The paste is typically applied to the landsusing a stencil. It is a gray material like putty. The composition of solder paste variesdepending upon its use.

E.g. Tin/Silver/Copper (Sn/Ag/Cu) or Tin/Lead (Sn/Pb). Flux is added to act as atemporary adhesive, holding the components until the soldering process melts the solderand makes a stronger physical connection.

Solder paste is typically used in a screen printing process in which paste is depositedover a stainless steel mask to create the desired pattern on a printed circuit board.

Figure 4.48

Definition: “Solder paste is an intermediate which connects the parts of printed circuits insurface-mount technology. It is the paste-type or cream-type made by blending a certainvolume of Lead, tin and special flux”.

Classification of Solder Cream:Pb solder:

• Sn 63%, Pb 37% most commonly used.
• Sn 62%, Pb 36%, Ag 2% Prevention of Solder Leaching.
• Sn 62.8%, Pb 36.8%, Ag 0.4% Prevention of Tombstone Phenomenon.
• Sn 43%, Pb 43%, Bi 14% Low Temperature Solder.

Pb Free solder (Lead Free):

• Sn 96.5%, Ag 3%, Cu 0.5% (0.3% Ag Pb free solder paste are also available)

Temperature and Stirring Time of Solder Paste:Storage Condition:

Solder paste should be stored in an airtight container at low, but above freezing, attemperature – 1 to 10C.

Keeping in Fridge:

Solder paste should be stored in an airtight container at low, but above freezing, attemperature – 1 to 10C.

Solder Mixing Procedure:

Update the removing time on information tag and in “Solder pastemixing report”.

After removing from refrigerator keep at ‘BEFORE AGING AREA’for 2 to 3 hrs.

Do the time and date entry in check sheet.

Mix the solder paste (Stirring m/c) for 60 to 90 sec. at 1000 rpm.Keep the jar at ‘AFTER MIXING AREA’ only. Update the tag andreport.

Figure 4.49Solder Paste Stirring/Mixing Machine:

Figure 4.50Check Point for Stirring:

1. In case of reaching to room temperature, the stirring time needs to be reduced.

2. The stirring time is 3 to 5 minutes in case immediately being removed from fridge. (The method not recommended)

3. Excessive stirring brings chemical decomposition with the lapse of time.

Information Tag for solder paste jar:Batch No.Out DateOut Time

Mixing TimeExp. Date

Figure 4.51

Check Sheet:

Solder Paste Mixing Details

_Date IDMixingOperatorVerified_Date IDMixingOperatorVerifiedNo.TimeSignBy QANo.TimeSignBy QA

Note: 1. If open Solder paste jar is not used within 24 hours, scrap the solder paste.

2. Keep un-used solder paste jar back into refrigerator, if not used up to 4Hrs.

3. Before mixing keep the solder paste at room temperature for at least 2 Hrs.

Figure 4.52Degree of Difficulty Occurs During Solder Paste Printing:The 0.5mm CSP, 0603 chip needs inspection, due to the higher level of difficulty inprinting than 0.4mm QFP, for guaranteeing the quality print after selecting solder,designing screen, setting up print parameters, managing and reflowing.

Standard Reflow Profile for Pb Solder Paste: Figure 4.53Standard Reflow Profile for Pb Free Solder Paste:

Figure 4.54

4) Under-fill:

Under-fill is the process of applying epoxy to fill the area between the die and the carrier.It used to control the stress on the solder joints. This stress is caused by either thedifference in thermal expansion between the silicon die and the carrier or physical stressescaused by vibration or drop shock. Once cured, the under-fill absorbs the stress, reducingthe strain on the solder bumps and greatly increasing the life of the finished package.Under-fill is typically applied using a capillary flow process in which material isdispensed next to a bonded flip chip and allowed to “wick” under the die.

IQC Process:
Check the material Qty and its documents before receivingfrom store.
Check the material for damage.Check the Mfg. and Expiry Dates.If not OK, return back to store.
Check the contents with Quality report.
Attach a detailed information tag.
Store the bottles in refrigerator at 1 to 10C. Follow theFIFO.
Use Procedure:	Figure 4.55

Update the removing time in “In & Out Consumption Report”Keep the U/F 2-3 hrs at room temp. Make different area of FORAGING & AFTER AGING.Take the U/F to use on line from AFTER AGING area only.

Figure 4.56

Direction for Use:

Dispensing Under-fill:

Keep the under-fill at room temperature for 2 to 3 hrs, then load into equipment fordispensing. Volumetric pump, auger, time-pressure and other dispense systems may beused. However, no matter what method of dispensing is used, it is important to make sureno air is mixed into material prior to, or during use. When dispensing, avoid using patternsthat will trap air.

(1) Select a dispenser type:

a) Hand dispense or time pressure valve – least expensive.

b) Auger style valve – acceptable: not giving good repeatability, thus more suitablefor large die.c) Linear piston pump – recommended: highly accurate when used for both large &

small die.

(2) For

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Curing

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Curing

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