FAQ's - Vapour Phase Reflow Technology
Gemini Tec use the very latest processing technology available to manufacture customer PCBA products. We operate with two Asscon vapour phase reflow ovens, providing customers with seamless PCBA processing from early prototype through to batch production. Gemini Tec are the first UK CEM to operate the latest in-line vapor phase reflow oven, manufactured by ASSCON of Germany.
We have listed out some of the FAQ's about this technology:
Why use vapour phase reflow, instead of other popular reflow methods?
Assemblers in progressive companies such as Gemini Tec recognise the advantages of this soldering method as the simplest and most reliable method of soldering. It allows for the processing of ALL types of components and PCBA's without many hours of complicated calculations to create thermal profiles, which are often a compromise between the solder paste and the component make up.
Vapour phase reflow is a repeatable process, without external factors that drive the process window.
How does it work?
A Galden liquid boils to deliver a layer of saturated vapour which contains no oxygen or other gasses. As the PCBA is immersed into the vapour zone, the vapour condenses onto the PCBA and transfers its corresponding heat in a linear method. Click here to read more about this unique process.
Vapour phase reflow was popular in the 80’s, but went out of favour due to chemicals that contained CFC’s, is this still the case?
The fluid used in today’s vapor phase machines do not contain any harmful CFC’s. The chemical is environmentally compatible, non-corrosive and extremely stable.
Are vapour phase machines expensive to run, which pushes up manufacturing costs?
No, the chemical running costs of a typical machine is around 70p an hour or a little over 1p a minute. Our Asscon vapor phase oven also consumes much less power, running at at 2.5kW p/h VS the equivalent convection oven running at 20kW p/h. The investment into the process is alot higher than a typical convection reflow oven, but ROI is seen very quickly through finished yields and removal of other hidden costs.
Is condensation soldering different to vapour phase soldering?
No, they are the same. The same fluids are used and heated to their boiling point to create a vapour, which allows the solder to reflow in an inert atmosphere. The only differences are to the individual manufacturer’s machine design.
Can PCBA products be overheated, much like a convection oven?
No, the maximum board temperature is equal to the boiling temperature of the liquid used, i.e.200ºC. for SnPb or 230ºC for lead-free materials. Irrespective of how long the PCBA and solder material remains in the vapour, irrespective of board thickness the temperature can never exceed that of the relative vapour.
So if your PCBA is 0.5mm thick or at 2.4 thick with 18 layers using 2oz copper ground planes, both will get the sufficient heat required and neither will overheat. The laws of physics dictates the process is impossible to overheat the PCBA.
What about oxidation?
Vapour phase reflow produces a 100% inert/oxygen free soldering environment that eliminates oxidation problems. The vapour is heavy (in comparison to steam or air) and therefore displaces lighter gases, which are found above the vapour. In this method, the vapour creates a protective gas atmosphere even without the use of nitrogen, which is a highly expensive soldering process.
Does vapour phase reflow cause tomb-stoning?
The ability to completely pre-heat the board, according to the material/component requirements (see previous answer), and create a very gradual temperature rise will help avoid thermal stress and tomb-stoning.
Higher technology boards are high in mix and use components with small process windows, such as µBGAs, CSPs and flipchips. A uniform reflow is crucial, so how can vapour phase provide this?
During conventional reflow to ensure any hidden central joints are heated sufficiently, the temperature may have to be raised as much as 50ºC above the melting point of the alloy. Overheating of the external solder connections causing permanent heat related damage. With vapour phase the heat is drawn by conduction from a saturated vapour onto the PCB. The heat is distributed evenly throughout, irrespective of whether components have a high or low thermal mass. Reflow temperature differentials across the assembly are always less than 5ºC, as the delta T of vapour phase is only 5°C
How does vapour phase cope with lead free solder paste?
The temperatures that is required for lead free materials are more extreme. Typically this is +10% for wave soldering and +20% for reflow, these additional temperatures add even further risk of damage by excessive heat. Vapour phase is the only reflow process that allows you to change to lead free (for example: SnAg 3,5 with a melting point of 221ºC) without any danger of overheating the board or its components by using a liquid with a boiling point of 230ºC.
Is the solder wetting of lead free materials a concern?
Lead free alloys do not wet as well as SnPb, an inert atmosphere will be more important to employ the best possible soldering conditions to help overcome this problem. When using convection reflow the use of a nitrogen atmosphere will improve solder joints, but this adds excessive cost and is a process that is not widely adopted in the UK over concerns with the long-term reliability.
Vapour phase reflow soldering automatically provides a 100% inert atmosphere, without adding nitrogen (and without adding additional cost), to guarantee the best possible soldering conditions along with the best possible long term reliability with every use.
What about the problem of pop-corning during production?
As plastics are hygroscopic, humidity will get into the body of these components (e.g. BGAs). When reflow soldering this can lead to high pressure of the moisture trapped inside the components which is converted into steam and forced out under pressure during reflow. This can cause delamination of the substrate or 'pop-corning'.
The higher the reflow temperature needed for lead free alloys results in a greater the risk of pop-corning, therefore a maximum reflow temperature of 230ºC is the optimum process. And with no risk of heating the PCBa's above a maximum of 230ºC, vapour phase reflow provides a vastly reduced risk of pop-corning. All MSL related materials used at Gemini Tec are subject to baking prior to use, when required. We also have in house vacuum sealing machines and automated control over exposure time and labelling materials.
If we can help you with more technical questions or if you need our expertise, please contact us to arrange a site visit.
Gemini Tec support a wide range of customers and applications from prototype to medium volume production, our investment in processing technology, allows us to support complex and demanding PCBA products where reliability and conformance is essential.
Contact us to talk about your requirements in more detail. +44 (0) 1252 333 444