vapor phase technology 2011

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Presentation Overview

Basics of Lead Free VP reflow

Vapor Phase History

Vapor Phase Explained

Reflow Soldering Development

Challenges and Solutions

Convection versus Vapor Phase

Vapor Phase Profiling

Vapor Phase Samples

Conclusions

Questions

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• Understanding Reflow Variation – Peak temp

Planning a Lead Free reflow profile requires understanding

variation in the component material and process:

Lead free BGA’s can be shipped with many different alloy types

Most common are SAC305 and SAC105.

It has been found that BGA’s changing from SAC105 to SN100 and

suspected pure tin.

Why?

Because the cost of Silver is increasing, and to remove silver lowers the

cost to produce

Packaging suppliers are doing this without advising manufacturers.

We need to develop reflow for the worst case scenario: Pure Tin Balls

It is very important to study and understand the variation of the reflow system from load to load.

Typical in industry is to ensure that peak temperature is at 15 degrees above melt temperature of the solder.

Since we are dealing with a solder bump on the BGA – We also need to consider its melting temperature

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• What Time/Temp do we need?

First off – We need to generate soldering reflow

profiles using a thermocouple probe through the middle

of the BGA devices into the balls.

Second – We need to make sure that our solder

reflow peak temperature PT is above 232 C according to

the BGA bumps solder chemistry, and then also consider the variation of the Oven and the reflow profile.

The worst case scenario should be a PT=240 C

Third – We have to ensure that our solder time above 240 C is maintained at least 30 seconds for good

soldering, but the time above 217 C must not be longer than 150 Seconds per J-STD-020D

4


• But how Hot is Too Hot?

J-STD-020D advises the peak temperature (PT)

of devices for Lead free reflow is:

245 C for large plastic components, and

260 C for smaller plastic components

SO – If we stay under 245 C, then we don’t need

to review of the component manufacturers

specifications

BUT – If we go over 245 C, then we need to pull

spec sheets on all parts to ensure we are not

exceeding temperatures.

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• Why is Vapor Phase technology an advantage?

In the Vapor Phase – the peak temp (PT)

is set by the fluid boiling temperature point.

The fluid and the generated vapor temperature

is always between 240 C and 245 C

We can be assured the parts are within

J-STD 020D !

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Developed in the early 70’s, patented by Robert Christian Pfahl and Hans Hugo Ammann of

Western Electric and Bell Labs.

Used in high quality Military as well as Aerospace programs.

Heat is transferred when the hot, saturated vapor condenses on a surface and gives up its

latent heat of vaporization.

The fluid boiling point is the governing factor in peak temperature.

Vapor Phase History

Patented Vapor Phase (by

Pfahl and Ammann)

Two layer vapor phase

(by Tze Yao Chu et al.)

Combination of Reflow

Soldering and Wave

Soldering in a Vapor Phase

(by W. Scheel et al.)

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Vapor Phase Explained

The vapor encapsulates the entire surface

of the board, resulting in smallest ΔT at

very short dwell times of the board in the

condensing vapor (thermal equilibrium)

The heat transfer coefficients are roughly

ten times greater than the values that are

reached through radiation or convection.

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Reflow Soldering Development

PAST PRESENT FUTURE

ΔT~50ºC ΔT~20ºC ΔT~2ºC

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Past Vapor Phase technology :

Environmental concerns of the fluids being

used.

Lack of fluid selection (few boiling

temperatures).

An inherent problem with tombstoning and

voiding.

Limited automation capability.

Throughput limitations (PCBAs exposed

to the vapor process longer than the tact

time of the placement processes).

In-line batch carrier machines were more

mechanical, and prone to more

maintenance.

Today most of the challenges were addressed :

Environmentally-friendly

CFC free, non-flammable, and non-

toxic.

Blood replacement substance.

ION Chromatography and Surface

Insulation Test (SIR) showed no residual

contaminates on the PCB post-reflow.

Thermally and chemically stable (inert gas

atmosphere)

Perfluorinated fluids have a viscosity

double than H2O ( high molecular weight)

Colorless and electrically non conductive.

Large variety of boiling points

selection…PEAK TEMP:

200, 215, 225, 230, 235, 240, 260 C

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No more vapor phase related tombstoning


The main driving force controlling tombstones is the relative speed of the solder's wetting

action (ramp rate) at the each end of the component.

Vapor phase soldering have variable gradient control so the appropriate dropping depth is

determined for every product using patented SVP (Soft Vapor Phase) and SolderAutomatic

resulting in a very accurate slope and reduced tombstones failures.

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Integration of a local vacuum chamber reduces void presence

Gases and flux residues are draw off from the joint, as long as the solder is molten

Results in a more robust solder joint.

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Fully automatic due to patented Soldering-Automatic and SVP PLC control.

Vapor phase efficiency improved when changing from product A to product B and completed faster than

the time taken up by the up-stream pick`n`place processes ( high throughput ≤ 15 up to 20

seconds/panel).

Can produce double sided SMT PCB’s at rates comparable to in line convection and IR reflow processes (

max. board size 800 X 650 X 80 mm).

Superior solder joint appearance. In-Line Batch carrier VP systems are capable of processing product B

board size changes while product A is still being soldered. PCB size adjustments can be completed, and

with IR pre-heat followed by VP soldering, there is no delay to change over once the sizing is completed.

Maintenance requirements for cleaning the system is minimized, flux residues are extracted on the

completion of each cycle.

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Vapor Phase maintains a low temperature on the BGA lid (made of a heat/moisture

sensitive plastic).

High convection temperatures causes the lid to warp down in the corners, a major cause

of bridging due to the use of poor BGA substrate materials.

Some component manufacturers have not redeveloped their original lead-processing

packages for lead-free temperatures, but have simply balled them with lead-free solder, or

they are offering a less-expensive, transitional package as they move to lead-free.

Vapor phase ensures that the difference in temperature ΔT between the solder balls is

under 2ºC.

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Conventional convection soldering machines

Capable of delivering the heat required for the lead-free soldering process, but process results vary.

The reflow zone changes are significant between the products.

Increased changeover time.

Larger soldering machines, along with increased necessity for protective gas add to the already high

energy requirements.

The process requires:

Additional energy

Protective gas

Larger machines

Delivered results are:

A high risk of thermal damages

Increased number of cold solder joints

Significantly higher emissions

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In convection ovens soldering track is further increased to avoid solder cracks and enable a smooth overall

temperature ramp up

In line vapor phase machines for high volume production :

Compact size (Length < 5 meters)

Delivers an 100% protective gas atmosphere as

part of the soldering process without extra cost

Solder Crack in L-leaded package Solder Crack in J-leaded package

Conventional Reflow

Soldering

Vapour Phase Reflow

Soldering

Nitrogen Cost

Indirect Energy Cost

Direct Energy Cost

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Reduced Cost

1/3 direct Energy consumption.

No compressed air required.

Reduced heat up of work shop saving

acclimatization cost.

Higher temperature substrate material can add 10 to 15% to PCB cost.

Standard FR-4 used as PCB laminate material rather than (higher cost) FR-406.

Fast setup for new products (wide range of products are processed with identical setup).

Delivers an 100% protective gas atmosphere as part of the soldering process without extra cost.

Low/No emission

Closed loop process prevents the vapor from escaping to the surrounding environment.

1. WPC-Loading

2. IR-Preheating

3. Vapor Phase

Soldering

4. Cooling

5. WPC-Unloading

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Vapor phase :

Overheating is physically impossible with proper fluid selection.

No cold solder joints due to determined heat transfer and absence of shadowing.

Best possible wetting due to fully inert environment.

Thermal transfer is independent of form, color, mass and mass distribution of

PCBAs.

Fixed peak temperature and superior heat transfer on thermally challenged PCB’s.

Superior thermal equilibrium offers processing advantages ( large mass connectors,

electrolytic capacitors, non-sealed switches and sensor devices)

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Shadowing of lower side of BGA

requires excessive temperature on

top of BGA

Unsoldered balls appear as a result

from shadowing effects

Vapor rises above and below the

BGA.

Heat transfer encapsulates the

whole assembly

No Shadowing

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Tin whiskers are small, thin metallic hair-like growths that naturally emerge from the

surface of solid tin (Sn). On lead-free tin surfaces, tin whiskers may grow to a length

sufficient to short one electronic circuit to another, creating product failure.

Tin melting point = 505.08K (231.93 C, 449.47 F)

With a 235 C fluid the vapor phase will reflow components tin coatings at the lowest

possible temperatures.

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Backward and Forward compatibility

Lead-free components are introduced in lead-based processes

Termination changes require additional modification to solder profiles and flux

chemistries to ensure proper wetting of the solder to the lead-free termination.

Nitrogen in convection reflow is becoming more a requirement than an option,

and nitrogen is expensive.

Backward compatibility – the majority of components are tin/lead, but some are lead

free.

Going with a higher reflow temperature for a few lead-free components will

affect adversely the majority of tin/lead components.

Forward compatibility – most components are lead-free, but some are still tin/lead

Using a lead-free profile may damage some of the tin/lead components

Vapor Phase is being considered as a solution to provide a middle-of-the-road compromise

reflow profile that dissolves the lead into the solder joint in a homogeneous mixture and

offer a higher reliability end-product.

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Convection reflow due to Lead free variables like melting point (between 217 C and 227 C) and the peak reflow

temperature (between 230 C - 260 C) can results in:

Affects reliability of via holes and the reliability of interconnections

The blue, green and red matte mask can peel off the board .

High thermal mass boards push the limits of convection reflow equipment

FR-4 substrate increased temperatures is causing thermal degradation or decomposition

Increased thermal expansion (CTE) compromise the structural integrity of the board ( Z-axis expansion of

FR-4 is greater at lead-free).

PT is causing plated through via barrel cracking, board warpage, and delamination.

Phenolic lead-free laminates are used which increase board cost by 10-15%.

Higher glass transition temperature Tg>170ºC

Low coefficient of thermal expansion (CTE) – lower Z axis expansion before and after Tg

In the Vapor Phase process standard FR-4 is used as PCB laminate material rather than (higher cost) FR-406

due to lower constant boiling temperature of the fluid.

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Vapor Phase reduces the intermetallic compound (IMC) thickness

As the IMC increases, the joint strength is reduced due to the brittle nature of the intermetallic.

It is recommended that SnNi IMC layers be within the range of 0.4 – 1.0 micro-meters and SnCu IMC

layers should be targeted in the range of 0.8 – 2.5 micro-meters.

The use of Vapor Phase Soldering for lead-free processes decreases the IMC thickness and the microstructure

shows finer secondary phases for profiles with peak temperature of 235ºC

Crack at PCB through IMC Layer

IMC growth made the joint more brittle

Intermetallic phase at a soldering time T=100s

Thic

knes

s of

the

Cu

-

Sn

layer

in

µm

Soldering temperature in C

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Soldered in Convection ovenSoldered in Vapor Phase oven

Vapor Phase increases visual appearance of solder joints

Finer structures

Less Oxidation

Better distribution due to increased wetting capabilities

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Solder Paste can be used after expiration date

With inert gas convection reflow no good solder joints could be made only 4 weeks after expiration date of the

paste.

With Vapor Phase soldering good solder joints could be established even 21 weeks after expiration date.

Paste within expiration date Paste after expiration date

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Profiling

Lean principals are applied to new product development.

New products are launched on production lines used in day to day operations.

Prototype lines are becoming harder to justify.

Matrix charts are developed on thermal mass, layer count, and complexity to get the profile close so the process development time is kept to a minimum.

VP reflow profiling can be classified by chemistry type, minimizing profiling time.

Advances in VP process systems allow machines to profile almost automatically.

Ramp rates and soak times at peak temperature can be defined by the engineer, and controlled by the systems regardless of the product mix during the process.

In a true one piece flow on a prototype, it is much easier to get it right the first time using VP processing.

The days of inadequate reflow temperature or over temperature on the first piece are virtually eliminated by use of the VP systems.

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Profiling

Pb

RSS (Ramp-Soak-Spike) for lead and RS (Ramp-to-Spike) for lead free are the top reference profiles for many

applications .

These profiles were characterized for each board using thermocouples at multiple locations on and around the

device.

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Profiling

Unique profiles were developed for each group of characterized products, based on:

Thermal mass

Distribution of copper planes

Loading patterns (distance between boards as they are loaded in

the oven)

IPC/JEDEC J-STD-020 classification.

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Profiling

BGAs /CSPs holes are drilled in the inner and outer

rows of BGA pads

BGA ball temperatures of inner and outer rows

must be within 2ºC of each other.

Minimum of 2 thermocouples per BGA/CSP attached to

a RF high temperature resistant recording device PTP

profiler which travels through the vapor phase reflow oven

with the panel under test.

Large components with high thermal mass require higher peak temperature for longer durations and small

temperature sensitive components require lower peak temperatures for shorter durations.

Four to six thermocouples should be attached at various component lead locations to represent the lowest to

highest thermal-mass

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Vapor Phase Samples

Cross-Section Samples

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Vapor Phase Samples

PCBA, Double sided, 12 Layers, with BGA‘s

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Vapor Phase Samples

SEM Solder Joints Samples

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Conclusions

Restricted resources, rising energy cost, increased awareness on the environment, increased demand for quality

at low operating cost, and the migration to PB-free components, urge a change towards vapor phase as the process

of choice.

Engineers are being challenged to establishes good processes up front, with minimal interference to operations.

VP soldering process assists the Engineer to get it right the first time, minimizing production interruptions.

VP reflow in inert gas atmosphere is not only a benchmark for other procedures but it defines an own unique

standard.

Vapor Phase reflow soldering is a technology from yesterday that will certainly see its comeback in the Lead Free,

Lean manufacturing environment of today.

vapor phase technology 2011

Technology