Like the SAGES of OLD said,"It all depends", and we can add "...for most
suppliers...".
The low cost standard FR4 (DICY based) we're testing has an Td onset of
312C and a Td failure of 322C (as built multilayer not virgin mat'l) . But
it also has a T260 time to delamination (for a finished multilayer) of
18.4 minutes and a virgin T260 TTD time of 24 minutes. This goes up to 42
minutes for thin cores (like 0.010"). This correlates to the lead-free
assembly process we are using that allowed us to pass these std FR4
multilayer boards thru LF assembly 8~9 times before delamination. This
was more than enough safety margin.
But I agree with Jeff, if the FR4 has a Td of 220C, better be cautious.
Happy Holden
APM
Jeffrey Bush <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
08/18/2005 12:39 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Jeffrey Bush <[log in to unmask]>
To
[log in to unmask]
cc
Subject
Re: [TN] New Resin System
I will caution that exceeding the base material onset of Td will affect
the electrical and mechanical properties and also you may see an
increased propensity for CAF. Standard FR4 for most suppliers has a Td
onset of 220C and a Td failure of 240C. The evidence of this may not be
readily apparent on the finished assembly and the affects post integrity
and interlaminate bonding are artifacts that we have seen on testing
standard FR4 materials in the 265-285 C range. These issues may be
manifest into the duty cycle of the units where failure costs are
highest.
I would recommend a move toward a filled system if your reflow temps are
above the Td of the base materials. Your PCB supplier should be able to
help you with the test program and transition into these new materials.
Jeffrey Bush
Director, Quality Assurance and Technical Support
VERMONT CIRCUITS INCORPORATED
76 Technology Drive - POB 1890
Brattleboro, Vermont 05302
Voice: 802.257.4571.21 Fax: 802.257.0011
http://www.vtcircuits.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Happy Holden
Sent: Thursday, August 18, 2005 12:21 PM
To: [log in to unmask]
Subject: Re: [TN] New Resin System
I want to echo David's advice. We have been testing the traditional
140C
Tg, DICY laminates in 2-sided, 4-layer & 6-layer stackups and all are
passing a lead-free assembly process with multiples of additional LF
cycles to spare. If you're board is simple enough, thin enough with
fewer
layers and the LF process is well engineered, you may NOT have to change
anything but HASL in order to make it "Lead-Free Capable" and "RoHS
Compliant".
Happy Holden
APM
David Hoover <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
08/18/2005 11:25 AM
Please respond to
David Hoover <[log in to unmask]>
To
[log in to unmask]
cc
Subject
Re: [TN] New Resin System
The word "filled" adds some further questions. If that is in reference
to
the laminate resin having filler additives they do provide less
expansion and can help with PTH reliability. However, the "filler" does
come
with a cost. This may greatly help with survivability on high
aspect ratio thick PCBs but it may also be unnecessary costs on low
layer
count PCBs. There really should be no "silver bullet"
material. The best "high rel" materials come with a serious cost
multiplier
and should only be used on those "big, thick, and ugly"
PCBs that really need them (or high temp environments where excessive
thermal cycles may be used). For the lower layer count
PCBs there should be a whole host of non-DICY materials that should take
care of their LF needs. If the PCB is thin enough and the
LF assembly temp is low enough, even DICY materials will survive.
Cheers,
David Hoover (aka, Groovy)
----- Original Message -----
From: "Tempea, Ioan" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, August 18, 2005 7:50 AM
Subject: Re: [TN] New Resin System
Joe,
a few months ago I had a chat with Dick Woolley of Tyco's PCB division.
He
recomended the phenolic filled resin systems as being a must requirement
for
a PCB supposed to be ready for lead-free. Although the verbage is
slightly
different, something tells me we are talking about the same thing.
Maybe he wouldn't mind if you contact him,
[log in to unmask]
Regards,
Ioan
> -----Original Message-----
> From: TechNet [SMTP:[log in to unmask]] On Behalf Of Kane, Joseph E (US
SSA)
> Sent: Thursday, August 18, 2005 10:27 AM
> To: [log in to unmask]
> Subject: [TN] New Resin System
>
> New Phenolic cured epoxy resin systems are being qualified to
> IPC-4101/24, 26, and 98 requirements.
> Has anyone tested these new materials? How do you know which material
> you are really getting
> (new Phenolic or old DICY cured epoxy resins)?
>
> Joe Kane
> BAE SYSTEMS
> Johnson City, NY
>
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