Vapor Phase reflow soldering is a technology from yesterday that will certainly see its comeback in the Lead Free, Lean manufacturing environment of today.

1. Executive Summary
Standard test boards populated with common components including BGAs and QFPs
were built with vapor phase and convection soldering technology and tested at Epic
Technologies, LLC facility. Reliability testing demonstrated that lead-free and tin-lead
joints produced by vapor phase to be equally robust as those from convection reflow.
The controllable, lower peak solder temperature makes vapor phase ideal for soldering
complex assemblies having sensitive lead-free SMT components
Vapor Phase Soldered, Lead Free, ENIG Surface Finish (U26 partially removed in
shear/tensile test)
Test Description
Tests were conducted using the Vapor Phase Reflow Process described by Dan Coada
at the August 2008 SMTA Orlando Florida presentation “Vapor Phase vs. in Lead Free
Complaint Assembly” 1
. EPIC Technologies LLC Test Vehicle boards were used with tin-
lead HASL or lead free Immersion silver, Immersion tin or ENIG surface finishes, as
appropriate. Boards were populated with tin-lead or lead-free components2, printed,
assembled and soldered using standard reflow or vapor phase production equipment.
The solder pastes selected for testing included tin-lead and lead-free no-clean and water
soluble formulations. Assembled test boards were thermal shocked between–45o
C and
+125o
C with 20 minutes duration at each limit for 500, 1000 and 2000 cycles in EPIC

2. Technologies LLC Failure Analysis Laboratory. Other test boards were subjected to
accelerated aging at 85o
C and 85% relative humidity for 1000 hrs. The EPIC Test
Vehicle is populated on only one side although it is equipped with plated through-holes
(PTH) for mixed technology tests. Test boards were populated with dummy 402, 603,
805, 68 pin PLCC, TSOP32, SOIC TQFP QFP208 and daisy chained BGA169 and
BGA352 components.
Convection Lead-Free Profile
Standard lead-free convection reflow profiles provided a peak temperature of 245o
C and
a time above liquidus (TAL) in the 60 – 90 second range recommended by paste

3. suppliers. Vapor phase soldered boards were soldered in an IBL CM800 vapor phase
soldering chambers using Galden LS/230 Perfluorinated heat transfer fluid. The vapor

4. phase profiles developed provided a TAL of about 90 seconds and a maximum
temperature of 230o
C, a temperature that is governed by the vapor temperature. After a
vapor phase profile is established, TAL can be modified to achieve any time required
without exceeding the 230o
maximum temperature. The vapor phase equipment first
preheats the board using infrared. Next, the work is lowered into the vapors at a
programmed rate to regulate ΔT and TAL. After the work reaches the maximum vapor
temperature, the duration of its exposure is preprogrammed. Several soldering programs
can be developed by the engineer and stored in memory to suit the needs of different
lead-free or tin-lead board types. ΔT and TAL are controlled by the program developed
by the engineer.
Vapor Phase Lead-Free Profile

5. Vapor Phase Tin-Lead Profile
Visual inspection for solder balls, tombstones, bridging, voids and dewetting indicated no
apparent difference between the two methods of solder joint creation. No tombstones
were experienced on the EPIC Test Vehicle boards in either case. Visual inspection
indicates that while vapor phase created solder joint performance and microsection
appearance on the board is very good, it might be a good idea to explore increasing the
lead-free TAL above the 60 to 90 seconds recommended by solder paste manufacturers
to accommodate thorough heat transfer to larger components, or clusters of large
components. Larger thermal load components, especially in clusters tend to retard the
complete melting of lead-free paste. It is more difficult to ensure good joints on
components with high thermal mass in convection processing because while trying to
achieve a sufficient TAL on larger components, smaller components in less populous
areas may tend to overheat. There is no chance of overheating smaller or isolated
components with vapor phase because vapor phase cannot heat a component higher
than the vapor temperature. Much discussion in trade magazines and forums such as
the IPC TechNet has focused on the question of soldering tin-copper and SAC alloy
terminated BGAs and other components with standard tin-lead solders. Using a 230o
C
vapor phase system, even liquefaction of these terminations ceases to be a problem

6. while posing little chance of overheating heat sensitive components. Similarly, risks
associated with lower tg substrates and temperature sensitive components is reduced
relative to lead-free convection processing. Since cleanliness had been studied using ion
chromatography for a previously published report1, a cleanliness comparison was made
for this report using ROSE techniques. An Omegameter operating above 100o
F was
employed. No differences were detected in ionic cleanliness between boards soldered
using convection reflow and those soldered in vapor phase. Lead-free no-clean samples
tended to have 50% higher contamination levels than standard tin-lead boards due to
the type and level of flux used in lead-free pastes. All results were well below IPC limits.
Resistance across soldered BGA daisy chain arrays of 40 and 80 joints were the same
for convection and vapor phase reflowed test boards within the limits of experimental
measurement. (Daisy chained dummy 169 and 352 termination BGAs containing 4 daisy
chains each were used) Solder joint conductivity did not appear to deteriorate
measurably after either 2000 thermal shock cycles or 1000 hours of accelerated aging at
85o
C/85RH. During the 2000 thermal shock cycles and accelerated aging, the average
absolute change in resistance on measured daisy chains is summarized in the following
table. The difference between the performance of Vapor phase soldered and convection
soldered test boards is insignificant considering the limited data set. The resistance
change for each sample is reported as the average of absolute values of the changes in
resistance for a set of samples. No special preparation or seasoning of samples was
performed. Resistance values were recorded “blind”. A small amount of ohmmeter drift
was experienced at the low resistances measured.
Average Percent Resistance Change (Absolute Value)

7. *Tin-Lead No-Clean resistance measurements tended to decrease slightly. Others
increased or were mixed, hence, the use of absolute values to assess changes. The
shear force required to cause SOIC joint failure was measured and found to be the same
for convection and vapor phase reflowed test boards. Shear force was measured on an
SOIC16 (U25 and/ U26) exerting a combination shear and tensile force which pushed
the component parallel to the plane while lifting the component by means of a 30o
wedge. These measurements did not deteriorate after shock and accelerated age. While
thermal shock results were measured at 500 and 1000 shock cycles, only those from the
2000 cycle test are reported here. Results are summarized in the following table.
Shear /Tensile force required to remove SOIC16 (pounds of force)

8. Conclusion
Thermal profiles using vapor phase soldering equipment are controllable with the
maximum temperature dictated by the specific thermal transfer fluid employed. The tin-
lead and lead-free solder joints created using vapor phase technology have equivalent
performance to those created using convection equipment, while offering a uniform fixed
maximum temperature of controlled duration. Vapor phase solder joint creation offers a
viable alternative to convection reflow. Convection reflow has less uniform maximum
temperatures over complex circuit board surfaces. Restricted resources, rising energy
cost, increased awareness on the environment, increased demand for quality at low
operating cost, and the migration to PB-free components, urge a change towards vapor
phase as the process of choice. Engineers are being challenged to establish good
processes up front, with minimal interference to operations. VP soldering process assists
the Engineer to get it right the first time, minimizing production interruptions. VP reflow in
inert gas atmosphere is not only a benchmark for other procedures but it defines an own
unique standard. Vapor Phase reflow soldering is a technology from yesterday that will
certainly see its comeback in the Lead Free, Lean manufacturing environment of today.

9. Source: EPIC TECHNOLOGIES LLC

10. Source: EPIC TECHNOLOGIES LLC