TECHNET Archives

February 2009

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Guy Ramsey <[log in to unmask]>
Reply To:
Date:
Tue, 3 Feb 2009 07:29:22 -0500
Content-Type:
text/plain
Parts/Attachments:
text/plain (195 lines)
I think, based on what we have heard so far, most likely there is too much
solder on the board.
This is a combination of too much paste and the solder contributed by the
HASL surface finish. 
I would try new stencil, .004" thick with reduced apertures between 80% and
90% of the pad.

Your 0.005" stencil with the 1:1 apertures may be fine for immersion tin,
silver, OSP or ENIG.  

Next likely, the parts may not be solderable. You might consider a simple
solderability test on the connectors. Print onto a piece of ceramic or bare
board, place the part in the paste and reflow it. Does solder wet the part
nicely? 

If you were baking anything but HASL I could also suspect board
solderability problems. Can you test on an unbaked board? Try one and see if
you still have bridging. It is still possible, especially if there is a
contaminate in the oven.

If the boards and components are really good and solderable even a little
slump should not be a problem. The solder should coalesce into a bead and
wet the pad and component to form a nice joint. 

One last thing you might try is obtaining a jar of paste from a different
lot. My experience with Kester 562 is very good and I doubt the paste is a
problem. It is possible.


 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Anselmo
Sent: Monday, February 02, 2009 5:30 PM
To: [log in to unmask]
Subject: Re: [TN] Bridging on SMD Connector

Ted,

The surface finish is HASL.  I agree, HASL is a hasl for these parts.
But our customer is unwilling (at this point) to let us change to finish to
ENIG or IMM tin.

The stiffener is a .020" FR4 bonded to the flex with .002" adhesive.

At what temp and for how long did you bake the boards prior to reflow?


John

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Ted Tontis
Sent: Monday, February 02, 2009 3:05 PM
To: [log in to unmask]
Subject: Re: [TN] Bridging on SMD Connector


John,
	What is the surface finish? Once had an assembly with a fine pitch
connector and a HASL finish on it and no matter what we did we had
consistent bridging. We tried electroform stencils, changed print
directions, changed pressure, messed with the apertures, and changed print
blades. Finally we changed the finish and it resolved the problem. 
	Also what type of stiffener is being used and what type of adhesive
is being used to keep it in place? I have worked with two flex circuits that
used PSA material to hold a heat sink in place as well as a stiffener, both
blistered in the oven at reflow temperatures. For the assembly with the heat
sink we would get a lot of draw bridging pillowing of components all of them
were components over the heat sink. For the fine pitch connector, that had a
stiffener under it, we had solder bridging and coplanarity issues. Baking,
prior to reflow, has greatly reduced the number of defects.  

Regards,

Ted    




Hi all,

I am having some difficulties with bridging on an SMD connector and need
some help.  
I've searched the archives for similar problems but have come up empty so
far.  Below are the details:

We are placing two different JMD connectors, one 60 pin and one 80 pin.
Stencil:  5 mil stencil and the apertures are 1:1 with the pads (.020"
pitch, .012 pad width)
Paste:  Kester R562 (use a new jar every day)
Parts: Flex boards with .010" stiffeners supported by carriers (the flex
panels are placed in a Durastone carrier that is recessed the thickness of
the panel).
Printer:  MPM model AP25

We are measuring the paste parameters after printing with the CyberOptics
2000.  The data shows lots of variation in paste volume and thickness.
I am not sure how accurate the data is since the Cyberoptics does not verify
correct alignment of the panel before it takes the measurement, but I do
agree we have variation.
In general, it shows the paste thickness to be .007" to .009".

We see slumping of the paste sometimes before placement, mostly after
placement.
I've changed the parameters of the printer (pressure, print speed, the snap
off distance to ensure we are getting on-contact printing).
I've also had the operator rotate the stencil 90 deg to see if there was a
difference in how we applied the paste (parallel or perpendicular to the
length of the aperture).
We are using metal squeegees on the printer.
All of the above changes have resulted in no noticeable reduction in the
number of bridges.

We are currently running a flex panel with 12 parts per array and we get 50%
to 100% bridging per panel. Now you see why I am pulling my hair out.

The room parameters (throughout the day) are 70 to 74 deg F and 25% to 30%
RH

My questions are:
1) What else can I look at that effects bridging?
2) Can the reflow (hot air forced) oven be causing some of the problem?
3) What should the paste thickness be with a 5 mil stencil?  
4) Should we go to a .001" reduction in the aperture on the stencil?  .002"
reduction?
5) Is our panel carrier causing the problem?
6) Will rubber squeegees make a difference?

Frustrated in Montana,
John

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or
(re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per
day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16
for additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100 ext.2815
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or
(re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per
day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16
for additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100 ext.2815
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or
(re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet
NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send
e-mail to [log in to unmask]: SET Technet Digest Search the archives of
previous posts at: http://listserv.ipc.org/archives Please visit IPC web
site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or
(re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet
NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send
e-mail to [log in to unmask]: SET Technet Digest Search the archives of
previous posts at: http://listserv.ipc.org/archives Please visit IPC web
site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------

ATOM RSS1 RSS2