Soldering of

Lead Free Solders

in

Vapour Phase

Heat Transfer

Heat Transfer Coefficient

Free Convection Gas 3 – 30

Water 100 – 1000

IR Reflow 50 – 100

Forced Convection 30 – 120

Vapour Phase reflow 400 – 700

Formation of an inert gas vapour phase

In the soldering area there is aliquid for creating vapour.

The liquid has a boiling point of e.g. 200°C for SnPb solders.

The container and the liquid has cooled down to environment temperature.

To form a vapour phase theliquid has to be heated up toits boiling point.

Than a rising vapour beginnsto form above the liquid

Formation of an inert gas vapour phase

Due to its high molecular weight thevapour pushes away the lighter gas (air).

This so called Vapour Phase is perfectly inert and contains no oxygen.

A clean inert gas atmosphere with 0 ppm oxygen is formed.

Within the vapour area a big reservoir ofenergy is available. By condensing of thevapour its energy will be transferred tocolder parts like electronic assemblies.

Even assemblies with a high mass can beheated up very reliable. In this process the temperature of the board can never exceedthe temperature of the ambient vapour.

Heat transfer process with a condensing vapour phase

The assembly is moved to the vapour phase. It was preheated by IR radiators from the top. It also can be preheated on the upper boundary of the vapour phase predominantly from below.

The use of IR preheat improves thequality of the solder joint and allows thefree shaping of temperature profiles.

The assembly dives into the vapour phase.There it is heated up. With a patented procedure it is possible to control the heat transfer to the assembly in a way that a softtemperature rise is performed.

Heat transfer process with a condensing vapour phase

The vapour condenses on theassembly and transfers its heat. Sincethe vapour is chemical inert it forms an inert gas atmosphere with 0 ppmoxigen.

This is done automatically without theuse of nitrogen.

The assembly can be heated up to a maximum temperature that equals thetemperature of the vapour. Thistemperature cannot be exceeded even if it stays longer inside the vapour. Thereforeno overheating is possible.

Heat transfer process with a condensing vapour phase

After leaving the vapour phase there is still condensed fluid left on the board.Due to the inner heat of the assemblythe liquid evaporates and a dry assembly leaves the machine.

The IBL Principle of a Vapour-Phase Soldering

Lead free solders for reflow soldering

•SnAg 3,5

•SnAgCu 0,6

•Melting point about 220°C!

•About 30°C higher than todays solderswith tin-lead alloy.

•Other solder alloys are discussed, but atleast in Europe not seriously accepted as alternatives.

Reflow soldering of Lead Free Solders

•No evolution of process development because using of lead free solders is a forced change inproduction materials because of legislativerules.

•Driving force is thinking in environmentalterms.

Consequences:

•There in no long term change in makingthe mainly used procedures better.

•A jump in process technology isnecessary as in the future the mainly used procedures like convection reflow are very limited in doing good lead free soldering athigher temperatures.

Main Problems When Soldering Lead FreeSolders

1. Thermal problems.When the temperature of boards or components exceed 230°C the danger of overheating and damaging is increasing rapidly.

2. Wetting problems.The wetting behavior of the lead free solders is significant worse than with leaded solders.

Therefore inert gas is much more important than today.

3. Repair problems.Due to the thermal level, necessary for repair, the board will be destroyed easily.

Procedures for Soldering Lead Free Solders

Convection Reflow•Advantages:

None

•Disadvantages:

Risk of cold or unsoldered solder joints.

Risk of overheating.

Bad wetting.

Inert gas is a must. (high costs)

Machines even longer than already today.

Procedures for Soldering Lead Free Solders

Vapour Phase Reflow•Advantages:

Can immediately be used without big preperation.

No risk of unsoldered solder joints.

No risk of overheating.

Best possible wetting.

Automatic 100% inert gas atmosphere.

•Disadvantages:

Until recently no high volume in line machines available.

Soldering of Lead Free Solders in Vapour PhaseWhich soldering machines can now be used for reflow

soldering these alloys?

Basically it is right that nearly every convection machine iscapable of delivering the heat, necessary for lead free soldering. But this has to be done without overheating theassembly. And this is the main problem!

Additional it has to be mentioned that the wetting of lead free solders is worse than that of leaded solders. Therefore an inertgas atmosphere is very important to have.

IBL Vapour Phase machines include allimportant features for lead free soldering

already today!1. A 100% inert gas atmosphere guarantees the best possible wetting for all solder alloys.

2. The maximum board temperature for lead free soldering canbe limited at 230°C. At this temperature it is certain thateverything is soldered. Even big BGAs on double sided boards.

3. All components and materials like FR4 that are in use todaycan be used without the danger of overheating.

4. All our machines, available today, can be used for lead free soldering immediately.

Vapour Phase machines in a variety of sizes, from

laboratory use to high volume production, are available.

Just test us!

VP-Reflow-Soldering guarantees the highest reliability.

Why?

The heat transfer by a condensing fluid is physicallyunequivocally determined.

VP reflow in inert gas atmosphere is not only a benchmarkfor other procedures but it it defines an own uniquestandard.

The heat transfer is reliable and reproducible to thehighest extend.

Main reason for the exact process behaviorof Vapour Phase Soldering:

1. Max. liquid temperature = boiling point of the liquid

2. Max. vapour temperature = boiling point of the liquid

=>The boiling point of the liquid defines the limits of the whole procedure.

=> Only one parameter is responsible for the maxium temperature of the electronic assembly.

Heat Transfer Liquids for Vapour Phase SolderingThe liquids, used in VP soldering machines for condensation heat transfer, have a range of important characteristics.

The special behavior of these liquids makes them extremely interestingfor reliable heat transfer to materials of all types and shape.

The most important features are:

•High stability (chemical inert)

•Environmental compatible

•No CFC

•Not dangerous

•Not combustible

•Non aggressive

•Electically non conductive

•High boling points

•High molecular weight

•Inert gas atmosphere (0 ppm Oxygen)

Depending on the kind and type of the liquid, boiling points of 150 -300°C are available.

For lead free soldering a boiling point of 230°C isrecommended.

Vapour Phase Reflowlöten

1. The vapour is heavier than air and comes always from below

2. The vapour raises above the PCB and transfers heat also from above

Vapour Phase Reflowlöten3. The vapour raises to BGA level and transfers heat directly tom the BGA

4. The vapour raises over the BGA

Vapour Phase Reflowlöten

•The heat transfer to the BGA works maximal, still without the possibility for the temperature to raise over the vapourtemperature.

•∆T close to zero.

•Required maximum temperature in the vapour is for SnPb solder 200°C, for leadfreesolders 230°C.

Vapour Phase ReflowlötenPopcorn-Effect

Plastics are hygroscopic. Therefore humidity is going into the mold mass of the BGA. While reflow soldering this can lead to high pressure rates of the encapsulated

water. This can cause delamination of the substrate, called "popcorning".

Temperatures above 210°C are known as more and more critical.

Vapour Phase ReflowlötenPopcorn-Effect

The most critical point is that popcorning is not easily detected since ithappens below the BGA.

With Vapour Phase soldering the risk of popcorning is minimized.

Vapour Phase Soldering Machine LV600

In line machine for high volume production

Max. board size:

automatic in line loading: 650 x 620 mm

manually loading: 650 x 640 mm

Transportation principle of the LV600

Vapour Phase Soldering Machines.Overview:

SMD line with a Vapour Phase machine LV600.

SMD line for MID-boards with a Vapour Phase machine SLC800i at the Moeller, Germany

Patented Repair process for High pincount SMD-Components

like QFP’s or BGA’s.

Automatic lift of component after solder is melted

PCB and Components remains uneffected and can be reused