In a message dated 2/15/01 2:31:47 AM Eastern Standard Time, [log in to unmask]
writes:
<< What are the optimum thickness for electroless copper and electrolytic
copper at via hole? >>
Tamir,
I am not exactly sure whether you mean "at via hole" as in a microvia, or
"in" a through hole via. I will answer as if you mean a through hole.
First - the electrolytic copper - FREQENTLY THIS IS SPECIFIED IN THE BOARD
PRINT, AND YOU MUST DO WHAT YOUR CUSTOMER ASKS. Now, if there is no copper
in-hole spec, 25 microns (1.0 mil) has been the accepted industry standard.
IPC acceptability documents allow a small +/- in the holes. (The reason I
say holes and not microvias, is that 25 microns on a microvia wall will
"plate shut" a 50 micron microvia.) Better distribution in the holes of high
aspect ratio through holes has been demonstrated using periodic pulse plate
rectification, also.
Second - the electroless copper - (Remember, about 20% of the boards in the
world are produced with direct metallization, not using electroless copper).
You need enough electroless thickness to withstand a clean/microetch step if
you are using pattern electroplating. This step removes any dry film
resisdues on the board surfaces, but also etches some copper from the holes.
Say your microetch step in pattern pre-plate removes 25 microinches (0.6
micron) of copper foil. The microetch may be more agressive on electroless
and remove 50 microinches (1.25micron). You must have a good copper coverage
in the hole after preplate cleaning to propagate the copper electroplate to
form a perfect plated "eyelet".
One way to check electroless deposit capability is to double the pattern
plate cycle clean/microetch, and then cross section a row of holes and
examine the plating coverage with a backlight test. If there are significant
points of light from exposed glass bundle ends, or even big areas of exposed
epoxy, you do not have enough latitude from electroless. Remember, if a
board is mis-imaged, you are going to strip the dry film, again prelamination
clean, and re-image the board. All this can remove copper from the hole, in
addition to the pattern plating clean/microetch.
Sorry, I cannot give you an exact thickness for your process. But I have
given you the procedure to allow you to easily set your electroless
thickness, depending on the severity of your pattern plate process. While we
sell electroless copper plating processes, we should be selling only enough
electroless to get good copper electroplating in the hole. Think of your
electroless process as insurance - buy only as much as you need.
Dennis Fritz
MacDermid, Inc
---------------------------------------------------------------------------------
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
To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
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
---------------------------------------------------------------------------------
|
