Hans,
As I said in my email, I have way too much time on my hands lately. Also, at
my advanced stage in life, I have few interests. Among them are the
lamination process, and what goes into making it effective and efficient,
and the soldering process. Therefore, I provide the following check list,
derived from detailed procedures I developed for the lamination process, in
addition to or as a summation of what we discussed off-line:
1) Materials (as indicated in the table in my SMTnet article), as glass
style (no matter what anyone else pronounces - never allow 7628 facing
copper except for cheap and dirty boards), resin to glass ratios, resin
systems and process requirements/conditions/parameters/specifications (press
cycles, etc.)
2) Assure proper design for "damming" (bleed lines, patterns, etc.) resin
flow during relamination - assures flow characteristics are adequate for
product not allowing too much, too fast or the reverse.
3) Material storage at receiving carefully managed
4) Material storage, especially prepregs (supplier recommended
refrigeration, dessication, vacuum storage, etc.), carefully managed in
layup area.
5) Prepreg holes cleanly punched or drilled, without damage, to allow proper
"float" during relamination
6) Copper foil, as ED - double treat or not with minimal pits, dents, etc.
Same for core and laminates.
7) Oxide treatment process and treatment quality as cuprous (red/brown oxide
- essential for polyimide resin systems) or cupric (black - suitable for
most epoxy resin systems but why bother). Oxide characteristics, as
attributes, include a smooth, even, velvety surface and texture without
water stains or other disruptions over the entire surface having been
treated. Of course, to see these conditions, the chemical process, and
chemistry within it, must be effectively managed. Also, ensure handling
procedures met as slip sheeting or whatever other methods to prevent oxide
damage as scratches or anything negatively affecting lamination process or
laminate integrity.
8) Even though IPC 600F allows pink ring, but at the caution of possibly
being a process indicator of other problems causing it, don't allow it or,
better yet, prevent it in your operation. If not, possible problems as
delamination or blistering around the hole wall may occur.
9) Specified process and equipment requirements as platten conditions
(parallelism [lead strip squeeze out and measurment], lack of dings or other
damage. Also required are determination of thermal and pressure
characteristics (all heater elements working as specified with even thermal
distribution in all press openings - measured with thermocouples [5 usually
per press opening], and/or electrical properties as current draw/amperage
measurement), and thermal performance as rise time. Also important are caul
plate conditions being ground very flat, as specified, and without dings,
nicks, tooling hole damage or out of spec conditions, and specified
thickness requirements met. Similar conditions required for any other
tooling plates or separator sheets. All these things required whether using
the old PSI or latest automated type presses.
10) Press cycles for particular laminate, core, and prepreg as specified by
supplier with modifications as required for your operation (number up in
press opening, thermal lag, etc.).
11) Of special interest, outside epoxies and modified epoxies (in and out of
the press in 90 minutes, or so, with no kiss going straight up to 350, or
so, PSI at 350 degrees F.), are those for polyimide and GETEK (very similar
cycles with very low pressure kiss possible then clearly specified
temperature rise and pressure increase over time, through critical process
windows, for up to four hours in the press to full cure for GETEK and less
for polyimide so as not to exceed 250 degrees Tg (270 possible but bond
strength and laminate integrity severely compromised)
12) Book making as core, detail, and prepreg layup. Very careful handling
required as well as attention to detail and procedures to ensure books as
specified so all layers in order and material layups as required. (number of
plies, order, etc.)
13) Careful attention to press loading per press opening as thermal/cure
considerations must be met as specified. Also, mis-registration problems may
be minimized with fewer books especially when made up of juicier pregs and
core material - more up with lower layer count and resin content possible
with the opposite true for higher. Per my article, and others, more
effective drilling operations may be assured to hit all the pads in their
centers when lamination process well managed - particularly at this stage.
14) Books also made up with separator sheets, release materials, and thermal
lag materials. All requirements critical for final product quality. Thermal
lag critical for polyimide and GETEK
15) Use whatever suitable means to transport books to press openings
depending on product while ensuring safe, effective, efficient operations.
16) After all the foregoing, ensure the required press cycle performed for
the material and product selected. Also, ensure specified cool down cycle
effected.
17) Remove press loads and perform required flash removal process while
ensuring proper handling especially to avoid edge delamination.
Enjoy the heart and soul of the MLB operation and don't forget that when
it's out of the press, it's too late for corrective or preventive action,
Earl Moon, Proof Of Design
---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------
|
