Subject: | |
From: | |
Reply To: | |
Date: | Tue, 30 Jul 1996 11:00:54 -0700 |
Content-Type: | TEXT/PLAIN |
Parts/Attachments: |
|
|
On Fri, 26 Jul 1996 14:51:00 -0700
[log in to unmask] wrote:
> From: [log in to unmask]>
Date: Fri, 26 Jul 1996 14:51:00 -0700
> Subject: PWB stretch
> To: [log in to unmask]
>
>
> TO:[log in to unmask]
>
> PWB stretch or shrinkage seems to be the limiting factor for stencil
> printing of larger PWB's with fine pitch pad's. We use laser cut stencils
> and stencil printers with visual alignment but still have problems with
> larger PWB's.
>
> What is reasonable to expect from PWB suppliers?
> Does anybody know about a specification for PWB stretch? I would like to ask
> for a stretch / shrinkage tolerance depending on PWB size and smallest pad's
> on the PWB. What can be expected on FR4 boards without paying a premium?
> What can be supplied at higher cost?
>
> Thanks in advance for any help on this
>
> Klaus Giese
> Siemens Energy & Automation
> Johnson City, TN 37601
> (423) 461 2459
> [log in to unmask]
>
> ***************************************************************************
> * TechNet mail list is provided as a service by IPC using SmartList v3.05 *
> ***************************************************************************
> * To unsubscribe from this list at any time, send a message to: *
> * [log in to unmask] with <subject: unsubscribe> and no text. *
> ***************************************************************************
>
Bill,
I hope the following information meets your need:
FROM MIL-S-13949/4D (16 August 1993):
MILITARY SPECIFICATION SHEET FOR GF BASE MATERIAL (I.E. FR4)
Dimensional Stability (for base material thicknesses less than .020 inch (0.51mm)).
After bake: Class A, 0.00075 inch/inch (0.00075 mm/mm) maximum;
Class B, 0.00050 inch/inch (0.0005 mm/mm) maximum
Same values are given for the 'after stress' condition.
Typical (nominal) values given in Laminate Suppliers' Product Data Sheets are:
< .0030 in/in (for thin cores <= .028"
< .0035 in/in (for thicker cores between .028" and .062")
Fred J. Paul, Sr. Process Engineer
PCB Operations, FLUKE CORPORATION
direct: 206 356-5734 fax: 206 356-6070
[log in to unmask]
***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to: *
* [log in to unmask] with <subject: unsubscribe> and no text. *
***************************************************************************
|
|
|