Agree witht that. Also, there seem to be no polygons placed on the routing
layers, which might add to the problem.

Igor

-----Original Message-----
From: Mark E Witherite [mailto:[EMAIL PROTECTED]]
Sent: Thursday, 4 April 2002 4:56 AM
To: Protel EDA Forum
Subject: Re: [PEDA] WANTED: PCB Expert (Off Topic)


My Money is on the mismatch of thermal coefficient of expansion between the 
copper and the nickle gold foil.

At 04:52 PM 4/3/02 +0100, you wrote:
>Many thanks,
>
>Details are as follows:
>
>6 Layer 1.6 FR4
>8" x 10" Board
>
>PCB support is a wasted rectangle 10mm wide along all edges, supporting PCB
>at 2 or 3 points along each edge.  (First observation is that this should
>have copper layers)
>
>Layer stack up is two cores + two foils (sizes rounded to 1 decimal place)
>
>R/P     Layer   Type                    thou
>-       -       Resist          0.4
>R       1       Ni/Au 0.5oz     1.1
>R       1       Foil 0.5oz              0.7
>-       -       Prepreg 7630    7.0
>P       2       1oz Copper              1.4
>-       -       Core                    15.0
>R       3       1oz Copper              1.4
>-       -       Prepreg 1080    5.0
>-       -       Prepreg 1080    5.0
>R       4       1oz Copper              1.4
>-       -       Core                    15.0
>P       5       1oz Copper              1.4
>-       -       Prepreg 7630    7.0
>R       6       Foil 0.5oz              0.7
>R       6       Ni/Au 0.5oz             1.1
>-       -       Resist          0.4
>---------------------------------
>Total                           64 = 1.625mm
>
>Effects are:
>Boards are flat from production, but twist on heating in solder reflow or
>wave solder.
>
>An analysis of 5 board produced 1 that exceeded the IPC warpage
>specifications.
>
>Trouble is all but one was too twisted to fit into the rack without effort.
>
>We had the same problem with the alpha version, but here this was put down
>to an incomplete plane
>on the two plance layers, this has been changed to a full plane - no change
>to warp.
>
>Suggestions so far have been to:
>0:      Add copper to waste (breakout) parts layers
>1:      Change the breakout to a waste part scored along the two long
edges.
>2:      Use a three core construction
>3:      Add copper hash to layers 3 and 4, (other either side of the two
>cores)
>4:      Change warp and weft of cores
>5:      Increase core thickness and decrease 1080 prepreg thickness.
>6:      Use 1.8 FR4 by increasing core thickness (undesireable)
>
>So far we've had no input from the manufacturer as to what (if any) of the
>above will be better, though
>they agree that all should have some affect (positive or negative) on bow
>and twist.
>
>We've also noticed that over a long period (weeks) the twist gets less.
>
>Regards
>
>Jason.
>
>
>-----Original Message-----
>From: Mike Reagan [mailto:[EMAIL PROTECTED]]
>Sent: 03 April 2002 16:43
>To: Protel EDA Forum
>Subject: Re: [PEDA] WANTED: PCB Expert (Off Topic)
>
>
>Jason
>Some of our advice is free
>What process is warping the boards?  Reflow or manufacturing? or upset
>employee?
>
>Mike Reagan
>EDSI
>
>
>
>----- Original Message -----
>From: Jason Morgan <[EMAIL PROTECTED]>
>To: 'Protel EDA Forum' <[EMAIL PROTECTED]>
>Sent: Wednesday, April 03, 2002 9:03 AM
>Subject: [PEDA] WANTED: PCB Expert (Off Topic)
>
>
> > Hi,
> >
> > We have a board warping problem and are looking for a PCB expert to help
> > resolve it.
> > (Preferably located in the UK, but not important)
> >
> > When I say expert, I mean *EXPERT*. The problem is quite complex and
>already
> > has baffled two manufacturers.
> >
> > We will pay the going rate for any consultation.
> >
> > Regards,
> >
> > Jason Morgan
> >

Mark Witherite  C.I.D.
Assistant Research Engineer
Astronomy & Astrophysics
Penn State University
2565 Park Center Blvd
Suite 200
State College, PA.  16801
email [EMAIL PROTECTED]
telephone 814 865 9839
fax           814 865 9100



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