CLTE consist of layers of glass cloth saturated with PTFE and partially
filled with ceramic powder.  It is difficult for the PTFE to completely
wet the surface of all the ceramic particles and you are left with
microscopic voids at this interface.  The test method used to quantify
moisture absorption doesn't adequately reflect what can happen with
ceramic filled PTFE dielectrics.

These materials should definately be baked (in a vacuum is best but not
absolutely necessary) prior to any thermal shock.  This includes prior
to lamination by the fabricator as well as prior to solder reflow by the
assembler.

Ron Desilets
Graphic Research
818/886-7340
> ----------
> From:         Alan Kreplick[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.;Alan Kreplick
> Sent:         Wednesday, February 03, 1999 7:30 AM
> To:   [log in to unmask]
>
> Hello Technetters,
>
> I'm relaying a problem as described by our Incoming Inspection
> Department:
>
> Board is a Hybrid constructed of Arlon CLTE and FR-4 material.   (2)
> top and
> bottom .020" Arlon CLTE layers are laminated to an FR-4 core .01933"
> thick, 4
> LAYER.  The surface finish is an immersion gold over (3-10 micro
> inches) over
> 200 micro inches of stress free nickel.  Approximately 90 % of the
> board edges
> are plated making connecting top and bottom side.  Board is used for
> RF
> applications.
>
> Board is double sided SMT and uses fixtures for placement and reflow.
> We have
> exhibited delamination (~ quarter in size) which is consistent with
> open end of
> the fixture.  Delamination
> was located with in the Arlon Ply material itself and not the FR-4 or
> copper
> foil.
>
> PCB vendor tested the raw material by thermal stressing and found no
> evidence of
> delamination.
> The PCB vendor also ran 70 bare boards through SMT Reflow facility and
> found no
> delamination failures.   We ran 10 bare boards in our operations and
> experienced
> a 60 % failure.  Delam was visible, once again, at the open end of the
> SMT
> fixture.   Machine profiles were reviewed by Process Engineers and
> found both
> sites compatible.   Differences that appear to stand out are that the
> PCB
> vendor's screen did not use a fixture.
>
> Questions:
>
> Has anyone had a considerable amount of experience with Arlon CLTE
> material and
> experienced similar problems when processing?
>
> Can moisture play a role in Arlon material - hygroscopic issues?  PCB
> vendor is
> located in
> Southern CA.   (Our assembly operations is located in New England.)
>
> Thanks in advance,
>
> Al Kreplick
> Sr. Mfg. Eng.
> Teradyne, Inc.
> Boston, MA
> 617-422-3726
>
> ################################################################
> TechNet E-Mail Forum provided as a free service by IPC using LISTSERV
> 1.8c
> ################################################################
> To subscribe/unsubscribe, send a message to [log in to unmask] with
> following text in the body:
> To subscribe:   SUBSCRIBE TechNet <your full name>
> To unsubscribe:   SIGNOFF TechNet
> ################################################################
> Please visit IPC's web site (http://www.ipc.org) "On-Line Services"
> section for additional information.
> For technical support contact Hugo Scaramuzza at [log in to unmask] or
> 847-509-9700 ext.312
> ################################################################
>

################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe:   SUBSCRIBE TechNet <your full name>
To unsubscribe:   SIGNOFF TechNet 
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################