Hi,

Please tell me some of the pad dimensions on your fine pitch devices.
Please tell us which flux/paste you are using.
Please tell us what thickness of stencil you are using. (Tell us what
material and cut)

If you are using 20 thou (mil) pitch, then I reccommend printing 10 thou
strips of paste. Keep them the full length of the pads. Many people try to
reduce the apertures in the length aswell as the width to prevent bridging,
but it's not neccessary.

So an example of pad dimensions for a device might be 12 X 70 thou. Print 10
X 70 thou strips.

On 25 thou pitch, the pad dimensions might be 14 x 70 thou, print 12 X 70 thou.
               or the pad dimensions might be 16 X 70 thou, print 14 or 12 X
70 thou, obviously 12 will have reduced risk of bridging.

The stencil thickness should be 6 thou, we use 7 thou thick but maybee your
paste might not suit this. Obviously 8 thou thick is too much for fine pitch.

A reason for bridging might be aspects to do with your paste/flux. Perhaps
the level of activity is too low. Please tell us what you are using.

Manila must have a high relative humidity, perhaps the temperature and
humidity in your production area is not working well with your paste. A
paste which works well with your climatic conditions might need to be
chosen. Please tell us what temp. and relative humidity you have in the area.

Please tell us what oven you have too.

Regards

Eddie Brunker
Tadpole Technology
Cambridge, UK
+44 1223 278200
e-mail [log in to unmask]


At 11:19 25/06/98 +0000, you wrote:
>Hi!
>
>I would like to ask for an effective stencil aperture design for
>fine-pitch ICs. We are encountering some solder bridging on these
>ICs. Also, there are solder balls present beside these components.
>Do you have any stencil design guidelines that you could share with
>us to improve our Screen Print Process?
>
>Also, Are you familiar with intrusive reflow? Can anyone share some
>informaiton about this?
>
>We also have a product that uses a MELF SMD resistor. The problem
>that we are encountering is that this component rolls during solder
>paste curing. So when it comes out, the component is already
>misaligned. Do you have any suggestions to control this without using
>any fixtures?
>
>Thanks.
>
>Regards.
>Jon Cruz
>Electronic Assemblies Inc.
>Manila, Philippines
>e-mail: [log in to unmask]
>Tel #: 823-7317/7593885
>Fax #: 7538629
>
>################################################################
>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 web site (http://jefry.ipc.org/forum.htm) 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 web site (http://jefry.ipc.org/forum.htm) for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################