I would really appreciate getting the forum's viewpoint on via plugging with soldermask... There seems to be little reference material I can find on the subject...
Please explain the process...
What are the key concerns with plugging vias with soldermask?
What are the hole size limitations?
How is that affected by board thickness?
What is the optimum hole diameter to use for a given board thickness?
What are the worst case hole sizes to use large and small?
How should this be specified on the fab drawing?
Thank you in advance for all your help.
Bill Brooks
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna
Sent: Tuesday, October 13, 2009 12:09 PM
To: [log in to unmask]
Subject: Re: [TN] Lifted Leads
Agreed.
Linda, to the best of my knowledge Akrometrix is the only source for coplanarity during reflow. They offer testing services.
http://www.akrometrix.com/testingservices/index.php
Chris
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Tuesday, October 13, 2009 1:43 PM
To: [log in to unmask]
Subject: Re: [TN] Lifted Leads
I agree with that assessment. Board warpage can be a contributing factor also.
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Tuesday, October 13, 2009 12:37 PM
To: [log in to unmask]; Stadem, Richard D.; [log in to unmask]
Subject: Re: [TN] Lifted Leads
Hi Linda & Dean,
While I take Linda by her words, 'pad cratering' is not out of the question, since the leads on connectors, whether they are gullwing-shaped or not are notoriously on-compliant.
In either case, the underlying root cause is connector body warping; for 'lifted leads' on heating and for 'pad cratering' on cooling.
Werner
-----Original Message-----
From: Stadem, Richard D. <[log in to unmask]>
To: [log in to unmask]
Sent: Tue, Oct 13, 2009 10:23 am
Subject: Re: [TN] Lifted Leads
Hi, Linda
I think what you may be seeing is more commonly called pad cratering, a common
issue with lead-free soldering. This shows up mostly on BGAs with their
relatively non-compliant connections, rather than gullwing leads. However, I
have seen it happen on gullwing connectors, where the body of the connector is
fastened to the PWB such that the compliant leads pull so hard as to lift the
pads during reflow and cooldown. This can be confirmed using shadow moiré
photography, where the image is strobed a number of time s during the temperature
cycle in order to show the physical movement that takes place.
Rather than pursuing the visible confirmation of lead coplanarity during reflow
using shadow moiré photography, you may be better off researching the
cause/corrective actions of pad cratering.
Simply search the archives of Technet or Google up the term "pad cratering" and
you will get a wealth of information, causes, and corrective measures to
eliminate the issue. It can be caused by a number of design and process factors
working together.
-----Original Message-----
From: TechNet [mailto:[log in to unmask] <mailto:[log in to unmask]> ] On Behalf Of Linda Langley
Sent: Tuesday, October 13, 2009 9:02 AM
To: [log in to unmask]
Subject: [TN] Lifted Leads
Linda
I know that you are signed on TechNet
Could you please post question to all experts for me:
We are reflowing 50pins CF card SMT connector and having high rate of the lifted
leads (they are gull wings leads). We measured leads co planarity using CMM
before reflow and it seems that all leads are meeting the spec.
My guess is that the component body is bowing during reflow process (we are dong
Pb free reflow with the peak of 234°C) causing lifted leads.
Somebody told me th
at there is a lab who can measure leads co planarity during
reflow cycle. Is anybody aware of such as test?
Thank you
Can anyone share some information, any help will be greatly appreciated.
Linda Langley CIT
Training Specialist
Jabil Circuit
248-292-6176
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