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January 2006

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Subject:
From:
Jeffrey Bush <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Jeffrey Bush <[log in to unmask]>
Date:
Fri, 20 Jan 2006 08:48:29 -0500
Content-Type:
text/plain
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text/plain (125 lines)
RO 4350 has a lower bond strength when compared to FR4.  TO combat this,
a higher profile foil is used to improve the peel performance.  When the
PCB house uses 4350 in a foil build and is bonding with RO 4450, the
foil treatment needs to be specific to maintain bond strengths.  Not
using the correct foil type will produce poor bond strengths which maybe
a learning curve for the PCB house.  

If the build is a core build, with RO4350 from L1/2: Ln/Ln-1, then the
bonding mechanism is controlled by Rogers.  The PCB supplier should be
able to interface with Rogers to obtain the lot testing information and
assess of the peel numbers are out of specification.  

A microsection of the PCB will also show the foil profile
characteristics and determine the build used.

Jeffrey Bush
Director, Quality Assurance and Technical Support
VERMONT CIRCUITS INCORPORATED 
           76 Technology Drive - POB 1890 
              Brattleboro, Vermont 05302
                Voice - 802.257.4571 ext 37 
                    Fax - 802.257.0011
                       <http://www.vtcircuits.com/> 
                           

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Thursday, January 19, 2006 5:09 PM
To: [log in to unmask]
Subject: Re: [TN] PWB SMT pad retention

The boards are made of Rogers 4350 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Sherif Refaat
Sent: Thursday, January 19, 2006 11:31 AM
To: [log in to unmask]
Subject: Re: [TN] PWB SMT pad retention

Hi Richard,

What kind of laminate is that? I had similar problem, few years ago,
repairing boards built using "Thermount" (Aramid). That was one of the
draw backs of this laminate. The new version of "Thermount" suppose to
be better in terms of peel strength, but I don't know if it is close
enough to that of FR4.

Sherif Refaat,

----- Original Message -----
From: "Stadem, Richard D." <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, January 19, 2006 11:42 AM
Subject: [TN] PWB SMT pad retention


Hi, Folks,
Is there a standard that specifies how well SMT pads should adhere to
the pwb? By pads I mean BGA pads that have no trace attachment, and I.C.
(gullwing) pads.
A client has circuit boards with pads that come off extremely easily
during standard rework and reflow processes. It is not limited to the
BGA pads, many other unused I.C. lead pads are also being found out of
place in the solder joints after reflow, and are easily peeled away. The
pads are not tiny flip chip pads, but standard .035" diameter pads and
rectangular .020" by .030" pads. The reflow peak temperature is only 210
deg. C for about 40 seconds. The rework is at 200 C. for 30 seconds.
Also, any speculation on the cause? This problem is limited to a single
PWB part number.

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