Soldering of Lead Free Solders in Vapour Phase

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 a liquid 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 the liquid has to be heated up to its boiling point. Than a rising vapour beginns to form above the liquid

Formation of an inert gas vapour phase Due to its high molecular weight the vapour 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 of energy is available. By condensing of the vapour its energy will be transferred to colder parts like electronic assemblies. Even assemblies with a high mass can be heated up very reliable. In this process the temperature of the board can never exceed the 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 the quality of the solder joint and allows the free 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 soft temperature rise is performed.

Heat transfer process with a condensing vapour phase The vapour condenses on the assembly and transfers its heat. Since the vapour is chemical inert it forms an inert gas atmosphere with 0 ppm oxigen. This is done automatically without the use of nitrogen. The assembly can be heated up to a maximum temperature that equals the temperature of the vapour. This temperature cannot be exceeded even if it stays longer inside the vapour. Therefore no 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 assembly the 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 solders with tin-lead alloy. Other solder alloys are discussed, but at least 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 in production materials because of legislative rules. Driving force is thinking in environmental terms.

Consequences: There in no long term change in making the mainly used procedures better. A jump in process technology is necessary as in the future the mainly used procedures like convection reflow are very limited in doing good lead free soldering at higher temperatures.

Main Problems When Soldering Lead Free Solders 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 Phase Which soldering machines can now be used for reflow soldering these alloys? Basically it is right that nearly every convection machine is capable of delivering the heat, necessary for lead free soldering. But this has to be done without overheating the assembly. 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 inert gas atmosphere is very important to have.

IBL Vapour Phase machines include all important 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 can be limited at 230 C. At this temperature it is certain that everything is soldered. Even big BGAs on double sided boards. 3. All components and materials like FR4 that are in use today can 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!

Why? VP-Reflow-Soldering guarantees the highest reliability. The heat transfer by a condensing fluid is physically unequivocally determined. VP reflow in inert gas atmosphere is not only a benchmark for other procedures but it it defines an own unique standard. The heat transfer is reliable and reproducible to the highest extend.

Main reason for the exact process behavior of 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 Soldering The 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 interesting for 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 is recommended.

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 Reflowlöten 3. 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 vapour temperature. T close to zero. Required maximum temperature in the vapour is for SnPb solder 200 C, for leadfree solders 230 C.

Vapour Phase Reflowlöten Popcorn-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 Reflowlöten Popcorn-Effect The most critical point is that popcorning is not easily detected since it happens 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