iNEMI project evaluates BFR-free PCB materials
reflow process conditions:
effective Dk*
• 3x, 245˚C peak temperature hF laminate resin content 1ghz Dk 5ghz Dk 10ghz Dk 20ghz Dk
• 5x, 245˚C peak temperature rich/Poor
• 3x, 260˚C peak temperature
Material A Rich, 66% 4.026 3.931 3.886 3.836
• 5x, 260˚C peak temperature
(control) Poor, 55% 4.396 4.3 4.256 4.206
Analysis techniques
Material B Rich, 70% 4.242 4.16 4.125 4.09
The SMASPP2z test vehicles were assessed
using the SPP technique before and after
Poor, 53% 4.502 4.413 4.398 4.364
the assembly reflow simulations. This
Material C Rich, 73% 3.985 3.917 3.886 3.854
technique basically compares a time do-
main impulse, which is propagated down
Poor, 53% 4.499 4.421 4.389 4.356
a longer trace to one, which is propagated Material D Rich, 73% 4.019 3.959 3.933 3.902
down a shorter trace.
Poor, 53% 4.481 4.419 4.39 4.357
The technique outputs an ‘effective
loss tangent,’ which includes both the
Material E Rich, 73% 3.999 3.931 3.901 3.869
laminate loss tangent as well as the effects
Poor, 53% 4.45 4.368 4.333 4.299
attributed to Cu foil roughness. Skin ef-
fects are separated out, but the degree to
Material F Rich, 73% 4.285 4.198 4.161 4.124
which the Cu foil roughness exacerbates Poor, 53% 4.708 4.632 4.6 4.566
skin effects is generally not separated from
Material G Rich, 73% 4.064 3.978 3.942 3.906
the laminate losses.
Many field solvers do not account for
Poor, 53% 4.596 4.518 4.486 4.451
roughness in their output, and as such,
Material H Rich, 73% 4.19 4.1 4.062 4.025
the inclusion of these effects within the
effective loss tangents allows the user of
Poor, 53% 4.687 4.612 4.579 4.541
this information to ensure they are not
Material I Rich, 70% 4.109 4.016 3.98 3.943
overly optimistic in their modeled design
performance.
Poor, 51% 4.688 4.585 4.541 4.499
Material J Rich, 70% 4.154 4.055 4.01 3.963
MEB II evaluation
Poor, 51% 4.751 4.646 4.599 4.551
The Material Evaluation Board II (MEB II)
is Intel’s second-generation multifunction-
Material K Rich, 67% 4.056 3.964 3.928 3.895
al test vehicle that contains test structures
Poor, 53% 4.347 4.274 4.243 4.212
for electrical, thermal and mechanical
* Effective Dk: average of core and prepreg
performance evaluation. All suppliers par-
ticipating in the MEB II builds were asked
to provide build material details for their
Table 1. Effective dielectric constant prior to bake/reflow.
boards. Additionally, a brominated FR4
laminate was built as a control board.
are used as the source of flame retardancy not greater than 10 seconds.
are composed of Al and Mg inorganic Using Gould JTCS 1.0 oz., test data
Material evaluation results
compounds. In the case of P-based flame showed that the copper-to-laminate adhe-
Prepregs
retardants, the source could be either reac- sion was in the range of 5-9 lbs/in with
All prepregs tested consisted of 1080 style
tive phosphorous organic components or Materials B, F and K exceeding 8 lbs/in.
cloth, were tack free and of good quality.
particulates. The inorganic filler content The interlaminate adhesion is shown to
The resin content ranged from 64-70%,
ranges were found to be 1-32% by weight. be in the range of 3 lbs/in with Materials
the flow was 32-50%, and gel times were
F and K materials being the highest at 4-5
82–160 seconds. The prepreg glass transi-
Laminates lbs/in. Employing bond film as the oxide
tion temperatures ranged from 47-68˚C
Dielectric measurements were conducted alternative, the adhesion is shown to range
and the minimum viscosity was 50-146 Pas.
using both two- and four-ply copper clad between 2-3 lbs/in, with Material F having
The viscosity minimums are relatively low
samples according to IPC-TM-650 Methods values greater than 4 lbs/in.
compared to the brominated counterparts.
2.5.5.6 and 2.5.5.1B. The majority of The x, y, and out of plane thermal
The temperature of the minimum viscosity
the tested materials showed a dielectric expansion values for the various halogen-
was in the range of 132-160˚C. The filler
constant (Dk) in the range of 3.9-4.6 and free laminates, both below and above the
content of these prepregs was measured
dissipation factors (Df) in the range of glass transition temperature, indicated that
by removing the resin from the glass cloth
0.01-0.02, with Material B slightly lower at the in-plane expansion is similar to the
and then ashing the samples at 700˚C in
< 0.01 both at 1GHz frequency range. brominated materials, in the range of 17-22
the presence of air. An assessment of the
With regards to flammability require- ppm/˚C. The out of plane data indicated
chemistry type and the shape or size of the
ments, all laminates appeared to be meet relatively lower values with an average of
filler particles was performed by optical
the UL-94 V0 rating, although Materials I around 45 ppm/˚C below Tg. The lower
microscopy and electron dispersive meth-
and J showed prolonged side burning and out of plane expansion is due to the con-
ods such as EDS. In general, the fillers that
violated the T1 flame time requirements of straining properties of the fillers used
www.globalsmt.net Global SMT & Packaging – March 2009 – 11
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