After the article about vapor phase soldering presented last April, many clients and others have asked us a series of questions that we thought to summarize in this article, hoping to provide some answers to everyone.
1) why Use Vapor Phase Soldering Instead of Traditional Reflow Systems?
The vapor phase soldering method is currently the simplest and most reliable system for creating excellent solder joints.
Characteristics such as simplicity and efficiency are leading this soldering system to the worldwide success it deserves.
The electronics “community” is recognizing the undoubted advantages of this process, which allows soldering of all components without complicated calculations or temperature control systems. Vapor Phase soldering guarantees reliable long-term reproducibility of desired processing conditions.
2) how Does Vapor Phase Soldering Work?
The principle behind Vapor Phase or “Vapor Condensation” soldering consists of bringing an inert fluid to boiling point. When this liquid boils, a layer of saturated vapor NOT containing oxygen or other gases forms above it. Subsequently, the board is “immersed” in the vapor zone, which, upon condensing, transfers the necessary heat for soldering to the material for the strictly necessary time. The chemistry involved in this process is perfectly environmentally compatible; it is extremely stable and the fluid used for vapor phase soldering in today’s systems CONTAINS NO CFCs.
3) is Condensation Soldering Different from Vapor Phase Soldering?
NO, they are the same thing. The fluids used are the same, heated to their boiling point to create a vapor layer (or condensation state), which allows soldering in an inert atmosphere. The differences are only related to the design of the soldering machine.
4) how is the Risk of Thermal Profile Over-Temperature Managed?
The maximum temperature on the board equals the boiling temperature of the liquid used (by physical law it cannot go beyond). Regardless of how long the board remains in the vapor for soldering and the board thickness, the actual temperature cannot exceed that of the vapor. For example, it’s possible to solder different items simultaneously, such as a 0.5 mm thick board and an 18-layer board. With components that vary greatly in terms of size, pitch and/or colors…all will receive the “optimal” amount of heat for soldering, without overheating problems. Vapor phase soldering effectively eliminates risks due to overheating. The laws of physics govern this process and consequently overheating is impossible.
5) What Can We Say about Oxidation in the Vapor Phase Soldering Process Compared to Conventional Reflow Systems?
Vapor phase soldering creates 100% inert, oxygen-free saturated vapor, which effectively minimizes oxidation problems. The vapor is heavier (compared to air) and therefore displaces lighter gases above it. This way, the vapor creates a protective gas atmosphere without using nitrogen (as used in other reflow soldering procedures). Furthermore, operating at a lower temperature compared to forced convection reflow systems, the oxidation phenomenon is reduced.
6) is it “True that Vapor Phase Soldering Greatly Increases the” Tomb-Stoning Effect? (Phenomenon of Chips Standing up Soldered Only on one Side)
Indeed, our initial tests when we first started with this technology showed a tomb-stoning effect on some chips.
However, it’s just an initial situation that can be easily overcome from a technical standpoint.
Today’s boards are often heavily populated with very different and sensitive components such as BGAs, CSPs, and Flipchips. Solder points are mostly hidden and a uniform temperature profile is essential.
The Vapor Phase soldering system, thanks to its extraordinary heat transfer efficiency, is among the most suitable systems.
In fact, during conventional soldering (Reflow), to ensure that the hidden central joints of these delicate devices (BGA, QFN, FLIP CHIP) are heated sufficiently, the temperature may be raised up to 40°C above the maximum soldering melting point. Unfortunately, this can cause permanent damage to components due to overheating.
Using a vapor phase system, heat is exchanged through conduction via the saturated vapor in which the components placed on the PCB are immersed, in an extremely UNIFORM way, regardless of whether the components have high or low thermal mass.
7) What Happens in Lead-Free Alloy Soldering with Vapor Phase Soldering Systems?
It’s well known that the temperatures required for lead-free alloys are higher than the “old” Sn63/Pb37: typically 10% higher for wave soldering and about 20% higher for reflow soldering.
Vapor Phase soldering is “the only soldering process” that allows switching between lead-free and lead-containing components without risk of overheating the board or components themselves, even using a liquid with a boiling point of 230°C.
In fact, reflow temperatures with Sn63/PB37 alloy range between 220 and 230°C during the reflow phase.
In Vapor Phase systems, as repeatedly emphasized, an inert liquid is used with a boiling temperature of 230°C in our case, allowing us to simultaneously satisfy requirements suitable for both leaded and Lead Free alloys without problems!
8) how is the Wettability of Lead Free Alloys in Vapor Phase Soldering Systems?
Lead-free alloys have lower wettability compared to SnPb ones.
Being able to operate in an inert atmosphere is extremely important and useful, as it helps greatly to compensate for the lower wettability issue of lead-free alloys.
Using traditional forced convection soldering systems (Reflow), the use of nitrogen improves solder joints and wettability.
Using a vapor phase soldering system instead, it automatically provides a 100% inert environment, without adding nitrogen (and without additional costs). This ensures the best possible soldering conditions and long-term reliability for all production.
9) Does the Typical Pop-corn Effect of Components Present in the Reflow Process also Occur with the Vapor Phase Soldering System?
It should first be noted that some electronic components are particularly sensitive to “moisture (they are hygroscopic), for example BGA, QFP, QFN etc., but not only these components are hygroscopic, the printed circuit board is also hygroscopic; that is, it absorbs moisture. During the reflow phase (whether reflow or Vapor Phase) any ‘trapped’ moisture tries to escape, exerting very high pressure inside these components. (Depending on temperature, we’re always talking about tens of bars)”
This is due to the liquid being transformed into vapor too quickly and can cause substrate delamination, a phenomenon known as “pop-corning or delamination”.
The higher the reflow temperature (for example Lead Free alloys) the greater the risk of Pop-Corning. On average in forced convection reflow systems, the peak soldering temperature is between 245 and 250°C.
A reflow temperature of 230°C achievable through Vapor Phase soldering systems greatly alleviates the problem……..but attention, the problem remains. Moisture must be removed from the devices (whether components and/or PCB) with an appropriate Baking procedure.
We received an interesting question which we answer below
What modifications need to be made to vapor phase machines currently used for SnPb alloys so they can be used for lead-free soldering?
No modifications or additions are necessary. All you’ll need to do is possibly fill the machine with a fluid having an appropriate boiling temperature.
Prime has chosen Galden with 230°C as the boiling point.
10) Vapor Phase… …Some Curiosities!
In vapor phase soldering, components and boards are immersed in vapor. The liquid condenses on the cold board surface and its latent heat of condensation is transferred to the board, thus increasing the product temperature to the liquid’s boiling temperature.
It’s one of the most efficient heat transfer soldering systems.
There are two types of fluids available for condensation soldering:
-perfluorocarbons, for example, 3M Fluorinet, contains only carbon and fluorine
-perfluoropolyethers, for example, Galden PFPE, contains carbon, fluorine and oxygen
Both types of materials are chemically inert and have high dielectric strength and low viscosity. They are non-toxic and pose no spark or fire hazards, so operator safety concerns are limited to the vapor being at a high temperature. From an environmental perspective, both have zero ozone depletion potential and are not regulated as volatile organic compounds (VOCs), as they DO NOT contribute to ground-level smog formation. The boiling point of these liquids can be selected for the desired application: Fluorinert FC-70 and Galden LS/215, which are commonly used, both have a boiling point at 215°C, but perfluoropolyethers are also available with boiling points up to 260°C.
You can find more info here.
