iNEMI project evaluates BFR-free PCB materials
effective Dk*
least one 1000 cycle pass at the most severe
assembly precondition, but also had mul-
hF laminate resin content 1ghz Dk 5ghz Dk 10ghz Dk 20ghz Dk
tiple failures on coupons with less severe
rich/Poor
preconditioning. This indicates potential
Material A Rich, 66% N/A N/A N/A N/A fabrication issues which are confounding
(control) Poor, 55% N/A N/A N/A N/A
the IST results. Cross-section FA analysis
of selected failures are being examined to
Material B Rich, 70% 4.253 4.167 4.129 4.092
confirm the root cause of the early failures.
Poor, 53% 4.497 4.416 4.379 4.341
The through-hole IST coupon per-
formance indicated potential fabrication
Material C Rich, 73% 4.029 3.951 3.917 3.884
issues confounding the data as well. Only
Poor, 53% 4.495 4.427 4.399 4.366 two materials (E and J) passed 1000 cycles
for all the assembly preconditions. Two
Material D Rich, 73% 3.974 3.9 3.87 3.838
additional materials (G and H) had only a
Poor, 53% 4.461 4.397 4.367 4.334
few random failures prior to 1000 cycles.
Material E Rich, 73% 3.977 3.897 3.863 3.828
In general, the cycles to failure dropped for
the remaining materials as the assembly
Poor, 53% 4.45 4.369 4.333 4.297
conditions became more severe. Cross-
Material F Rich, 73% 4.318 4.231 4.192 4.154
section FA analysis of selected failures are
being examined to confirm the root cause
Poor, 53% 4.721 4.64 4.604 4.568
of the early failures on the through hole
Material G Rich, 73% 4.04 3.955 3.919 3.883 coupons as well.
Poor, 53% 4.563 4.481 4.447 4.411
Moisture diffusivity testing showed an
increase in the Dk of the materials tested
Material H Rich, 73% 4.153 4.064 4.029 3.994
from the dry condition to the fully satu-
Poor, 53% 4.654 4.572 4.538 4.5
rated condition.
Complete results for the MEB II
Material I Rich, 70% 4.085 3.989 3.951 3.914
testing were not available at the time this
Poor, 51% 4.681 4.583 4.543 4.502
report was developed. Two of the halogen-
free materials and the FR4 control material
Material J Rich, 70% 4.132 4.028 3.982 3.937
were not received in time to include their
Poor, 51% 4.735 4.63 4.583 4.535 results. In addition, several of the test
Material K Rich, 67% 4.034 3.943 3.906 3.871
results did not conclude in time to be in-
cluded in this. A full report will be issued
Poor, 53% 4.373 4.301 4.271 4.241
in the future.
* Effective Dk: average of core and prepreg
conclusions
Table 3. Effective dielectric constant after bake/reflow.
Our investigation showed that not all
halogen-free materials are equivalent, and
none is equivalent to our FR4 baseline.
was published. the worst registration tolerance. Most of
Compared to the baseline material, we
the boards were built with via registration
see generally higher Dk values and lower
Laminate material compatibility with tolerances of +/- 5-6 mils.
Df values for halogen-free materials. The
higher reflow temperature using the The dielectric constant of the halogen-
significance of the halogen-free material
HOP31B test vehicle free laminate materials as measured by
property and performance differences will
The cross section analysis of the HOP31B PNA showed similar overall ranges to those
be dependent on the design and demands
test vehicles showed that only one of the reported by other methods in this paper.
of the products in which they are incorpo-
halogen-free laminate materials exhibited The nominal Dk values were different for
rated.
characteristics consistent with thermal individual materials while the individual
While the dielectric constant was
degradation issues. This manifested itself Dk ranges were similar when looking at
relatively unaffected by the assembly reflow
as characteristic cracks radiating out from specific test structures. Loss measurements
processes, the effects on the effective loss
the PTHs in the resin rich PTH antipad were extracted as total loss in dB/in using
tangent were more noticeable, albeit not
regions. These cracks were present in both the PNA. The total loss is a combination
consistent. This may be due to the varying
the 40 mil and 80 mil thick test vehicles of the dielectric and copper losses for each
moisture content of the laminate materials
using Material D. test structure. Additional work is being
as manufactured at the laminate vendor
No inner plane separation was noted done to extract the dielectric loss from the
and PCB fabricator, and the relative sensi-
in any of the laminate material samples. total loss measured.
tivity of the loss tangent vs. the dielectric
IST results for the halogen-free
constant.
MeB ii results materials tested to date showed variable
As a class, with one exception, the
The via registration results ranged from responses (Table 5). Materials B, C, D,
halogen-free laminate materials did not
+/- 4 mils to +/- 8 mils for all the boards E, and H all passed 1000 cycles for all as-
exhibit resin cracking/delamination issues
measured. Fabricators 3 and 7, which built sembly preconditions on the microvia IST
normally associated with an incompatibil-
with materials F and K, respectively, had coupons. Materials F, K and G all had at
ity with higher reflow temperatures. The
14 – Global SMT & Packaging – March 2009 www.globalsmt.net
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