Ramon,
Tomb-stoning is more of a bulk solder to component interface effect...
The Ag surface stress leads to joint failure at the PCB pad to solder fillet
interface and is extremely rare except under extreme mechanical or thermal
conditions.
Paul Edwards
Process Engineering
[log in to unmask]
Tel: 408-433-4700
FAX: 408-433-9988
Surface Art Engineering
81Bonaventura Dr.
San Jose, CA 95134
DUNS: 944740570
CAGE/NCAGE: 1XZ48
-----Original Message-----
From: Dehoyos, Ramon [mailto:[log in to unmask]]
Sent: Tuesday, September 28, 2004 10:21 AM
To: TechNet E-Mail Forum; Paul Edwards
Subject: RE: [TN] ENIG vs. HASL plating with 0.5 mm pitch QFN components
Paul:
Does the extra surface tension create more tomb stoning?
And the concentration of stress results in potential for cracks?
Regards,
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Paul Edwards
Sent: Monday, September 27, 2004 10:09 PM
To: [log in to unmask]
Subject: Re: [TN] ENIG vs. HASL plating with 0.5 mm pitch QFN components
Paul,
I've been building, first prototype then production PCAs, with 0.5mm HASL
pads since 1991 with success... The HASL thickness variations are typically
around 0.0007" and are in fact many times less than the variations in the
QFP lead planarity.
The problem I see with Ag is two fold in nature:
1) Ag adds no volume to the solder joint and increases the surface
tension of the joint interface
2) Exposed Ag leaves low activation energy surface which can lead to
tarnishing. This then serves as a chemical reaction repository and surface
stress concentrator
Paul Edwards
Process Engineering
[log in to unmask]
Tel: 408-433-4700
FAX: 408-433-9988
Surface Art Engineering
81Bonaventura Dr.
San Jose, CA 95134
DUNS: 944740570
CAGE/NCAGE: 1XZ48
-----Original Message-----
From: Black, Paul [mailto:[log in to unmask]]
Sent: Monday, September 27, 2004 5:25 PM
To: [log in to unmask]
Subject: Re: [TN] ENIG vs. HASL plating with 0.5 mm pitch QFN components
I wouldn't feel comfortable using HASL for fine pitch parts. A past
fabricator I used for HASL of through-hole boards would only guarantee
thickness within +/- .001" and I can get a much flatter finish using Silver
for the same cost. Regarding the HASL process and Lead, it is true that the
current process will no longer be viable in the EU when the directives take
effect, but it is my understanding that the manufacturers of HASL equipment
are trying to adapt the process to the new SAC alloys.
Thank you,
Paul Black
Manufacturing Engineer
Kronos
E-mail: [log in to unmask]
Voice: (978) 947-1520
Fax: (978) 244-0568
www.kronos.com
Improving the Performance of People and Business(tm)
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Wenger, George M.
Sent: Monday, September 27, 2004 4:57 PM
To: [log in to unmask]
Subject: Re: [TN] ENIG vs. HASL plating with 0.5 mm pitch QFN components
Paul,
I didn't make any comment about planarity or indicate that HASL couldn't be
controlled and used for 0.5mm pitch because there are lots of companies
using HASL for 0.5mm pitch. The reason I wouldn't recommend HASL is because
of the pending RoHS/WEEE directives.
Regards,
George
George M. Wenger (908)-546-4531
Reliability / FMA Engineer
Base Station and Subsystems Group
Andrew Corporation, 40 Technology Drive, Warren, NJ 07059
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Paul Edwards
Sent: Monday, September 27, 2004 4:34 PM
To: [log in to unmask]
Subject: Re: [TN] ENIG vs. HASL plating with 0.5 mm pitch QFN components
Joe,
I disagree with Paul and George...
The planarity issue with HASL on .5mm pitch parts is over blown.
A good PCB fabricator can control HASL variations.
HASL increases the volume of solder in the lap joint and increases and
lowers the joint's bulk interface intermetallics.
Paul
Paul Edwards
Process Engineering
[log in to unmask]
Tel: 408-433-4700
FAX: 408-433-9988
Surface Art Engineering
81Bonaventura Dr.
San Jose, CA 95134
DUNS: 944740570
CAGE/NCAGE: 1XZ48
-----Original Message-----
From: Black, Paul [mailto:[log in to unmask]]
Sent: Monday, September 27, 2004 11:40 AM
To: [log in to unmask]
Subject: Re: [TN] ENIG vs. HASL plating with 0.5 mm pitch QFN components
Joe,
I would agree with George on both counts. In any case, I wouldn't choose
HASL. It doesn't deposit evenly. In the case of your fine pitch and small
components, you could end up with reliability issues.
Thank you,
Paul Black
Manufacturing Engineer
Kronos
E-mail: [log in to unmask]
Voice: (978) 947-1520
Fax: (978) 244-0568
www.kronos.com
Improving the Performance of People and Business(tm)
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Wenger, George M.
Sent: Monday, September 27, 2004 1:21 PM
To: [log in to unmask]
Subject: Re: [TN] ENIG vs. HASL plating with 0.5 mm pitch QFN components
Joe,
Were you asked to recommend the type of pwb plating that is best for your
simple board or were you only given two choices to pick from? If I had to
pick from the two choices I'd pick ENIG. If I had to make a recommendation
I wouldn't recommend either. My preference would be immersion silver.
Regards,
George
George M. Wenger (908)-546-4531
Reliability / FMA Engineer
Base Station and Subsystems Group
Andrew Corporation, 40 Technology Drive, Warren, NJ 07059
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Macko, Joe @ IEC
Sent: Monday, September 27, 2004 1:08 PM
To: [log in to unmask]
Subject: [TN] ENIG vs. HASL plating with 0.5 mm pitch QFN components
Fellow techs,
I have been asked to recommend the type of pwb plating that is best for a
simple board with only a few components. The finest pitch component is a
QFN, 64 pads, 0.5 mm pitch. There are some 0402 resistors and capacitors as
well.
My 2 choices are HASL or ENIG. Would someone please comment on which is
best for 0402 and 0.5 mm QFN type components.
Thanks in advance.
joe
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