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The Return of Vapor Phase Reflow Soldering
By Marc van Stralen, IMDES Creative Solutions
back. Introduced in the 1980s when surface mount technology was in its infancy, the process uses hot vapor and a special heat transfer medium that condenses on the PCB. The heat transfer medium used
C
in the early days was harmful to hu- mans and to the environment. As a result, vapor phase soldering lost its popularity and infrared (IR) solder- ing rose to become the standard. The arrival of perfluoropoly-
ether (PFPE) heralded the return of vapor phase soldering. PFPE is man- ufactured and marketed by Solvay Solexis under the brand name Galden®. PFPE is a liquid polymer, exclusively built up of carbon, fluo- rine and oxygen. The bonds between these atoms are some of the most sta- ble connections in the realm of car- bon chemistry.
Why Vapor Phase Soldering? For today’s complex BGA,
FPGA and next-generation, difficult- to-solder SMT components, this sol- der method is relatively easy for both professionals and amateurs to obtain excellent soldering results. Key features of the process in-
clude: high temperature resistance; chemical resistance — does not react with acids, alkalis or strong oxidiz-
In vapor phase reflow soldering, the condensation from a liquid heat transfer medium uniformly heats the PCB, melting solder and joining the components to the board.
During heat transfer, under normal atmospheric pressure, all types of Galden are thermally stable. It also allows for the repair and rework of major components, such as FPGAs, with simple auxiliary tools, without
up frequently between the compo- nents and the PCB. Stricter stan- dards were also being set for the quality and reliability of circuit boards.
The time was right for vapor The Flying Probe Experts TAKAYA
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Featuring 10-Flying- Z-axis including 4 vertical flying probes providing unequal access to test points.
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High end Laser measuring capabilities to compensate for board warpage.
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ondensation soldering, also known as vapor phase reflow soldering, is making a come-
ers; tolerates all known plastics, met- als and elastomers; low vapor pres- sure; and excellent dielectric proper- ties.
The process has no flash point,
so it cannot catch on fire, good wet- ting properties, low surface tension, and releases no harmful substances.
damage. PCBs with SMT components
are generally reflow soldered in an IR-heated oven, frequently with ni- trogen as a shield against oxidiza- tion. With the introduction of lead- free solder, the process became much more sensitive. Defects began to crop
phase soldering to be reexamined as an alternative to IR reflow soldering.
How It Works In a sealed chamber, the chemi-
cally inert and electrically neutral heat transfer liquid, PFPE, is heated to its boiling point. Once the liquid is boiling, a saturated vapor forms above it with practically the same temperature. Assembled circuit boards are
brought through the vapor, causing it to condense on their surfaces. The vapor condenses on the boards be- cause they are brought into the chamber at a lower temperature. This condensation process continues until the surface of the circuit board is brought up to the the same tem- perature. After that, the precipitated liq-
uid evaporates again. This is like bringing a cold glass into a warm room. First vapor condenses on the glass and then slowly evaporates as the temperatures balance. The soldering alloys, which
have a lower melting point than the temperature of the vapor, are entire- ly liquified. As the medium solidifies and the solder cools, the circuit boards are cycled out of the process chamber. The soldering takes place in a chamber filled with an inert gas so
Continued on next page
June, 2018
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