Dear Saunders,
A good elaborate info on the product and process with its concerns. I
understand there is a hole-fill material
called " FIBRITE" used for insulating the metal. Being in India, I am
unable to get the Product details including
the address and contact person who can supply the product. Looking for
help!
Regards,
M A Ranganath
GM - Technical & Quality
Sanmar Micropack Limited
Plot No.16, Jigani Industrial Area,
Bangalore - 562 106. INDIA
Phone: 91 - 80 - 7825223/224/226/389
Fax : 91 - 80 - 7825225
Email : [log in to unmask]
B2Saunders@AO
L.COM< > To: [log in to unmask]
Sent by: cc:
TechNet Subject: Re: [TN] Metal core PCB's
<[log in to unmask]
ORG>
05/24/02
09:43 PM
Please
respond to
"TechNet
E-Mail
Forum.";
Please
respond to
B2Saunders
David,
Metal Core Printed Wiring Boards are composed of three subassemblies (SA).
Two SAPWBs and the prepared Metal Core. The designs of SAPWB-A and SAPWB-B
must be conservative due to the inability to electrically test prior to the
final lamination set. The two SAPWBs should be symmetrical and the layer
facing the MC needs to be predominately copper; if it is a plane all holes
must have pads... if a signal flood with copper. The will greatly improve
the SA to MC bond line. Buried vias within the SAPWBs need to be avoided
as the number of lamination sequences will begin to deteriorate dieletrics;
especially Polyimide. The MCPWB configuration is excellent for Via In Pad
and I recommend using it right from the beginning. SAPWB layer to layer
separation needs to be .005 nominal. External layer line widths and
spacing facing the MC side need to be .005 while MCPWB external line and
spacings need to be .007 and .007 due to heavy copper. In! ner layers can
be .004 and .004, preferably .004 and .005.
The Metal Core itself needs to be prepared prior to lamination. Pre
machine so the MC edges are .060 in of MCPWB edge. I suggest EDM depending
on core type reducing induced stress, followed by re-annealing to eliminate
bow and twist; oil canning will kill the MCPWB. After drill aggressive
etch to deburr and reduce stress points. Design of the core needs to allow
minimum web and large clearance to the MCPWB PTH. MCPWB PTH that contact
MC can be quite challenging and should not be electrically Mission
Critical.
Lamination of the set varies from Suppliers. Two significant camps are:
Single lamination including resin fill for MC holes and cavities and;
(Second Camp) prefill holes and cavities of MC, plannerize, then laminate.
A critical component of reliability is the oxide to MC, without it
delamination will occur. A very nice non destructive method of final
lamination integrity is submerged water ultra sound.
MCPWBs require strict adherence to design rules. The cost is very, very
expensive and thus is regulated to smaller volume, high reliability types
of usage. Assembly will be costly as well. Design in "spare" holes for
future modifications and wiring.
Reexamine the two single sided assembly boards that can be bonded to a cold
frame it is the best packaging approach. The advantage of MCPWB is the
thermal management, some CTE control (depending on MC material and SAPWB
thickness), and the direct I/O to the SAPWBs. In the cold frame approach
signals must migrate to the "over the edge" connector. This "down the
drain" signal flow is reversed and spreads across the adjoining SAPWB. An
MCPWB PTH eliminates this effect very nicely. Multiple stacked Metal Core
Boards interfacing are ideal candidates for "Z axis" only I/O, such as
Elastomerics or compression type configurations which saves much cubic area
and eliminates half of mechanical I/O and associated cabling.
I have only touched the surface of parameters... Let me know if you want me
to continue because I can go on and on. Good fortune in your endeavor.
Boston Brad
Bradford Saunders
PCB Product Engineering
www.CORETEC-Inc.com
781 858 0783
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