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June 1999

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Subject:
From:
Mike Meanor <[log in to unmask]>
Reply To:
"TechNet E-Mail Forum." <[log in to unmask]>, Mike Meanor" <[log in to unmask]>
Date:
Wed, 9 Jun 1999 13:24:26 -0700
Content-Type:
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I have recently received a notification from a customer of mine that states:

"Clarification of heat sink/ground plane vertical fill of Solder requirements, referenced in IPC-A-610B page 52 Figure 4-2 and associated paragraph."

In the notification the author writes that, per agreement with an IPC Master Instructor at MTTC (Manufacturing Technology Training Center), there is an error in the book.

IPC-A-610B page 52

Acceptable Class 1 & 2
Nonconforming Defect - Class 3
As an exception to fill requirements on Table 4-1 on thermal heat sink planes plated through holes, a 50% vertical fill of solder is permitted, but with solder extending 360 degree around the lead with 100% wetting from barrel walls to lead on the solder side.


The error is stated:

Because there is less solder allowed in the PTH for Class 1 & 2, what solder is there must have 100% wetting to both barrel and lead as viewed from the primary side with solder extending 360 degrees around the lead on the solder side.

New standard/requirement:

Class 2
All heat sink/ground plane holes must have 100% wetting of barrel to component lead on the primary side. 

Class 3
75% solder fill is required on PTH attached to heat sinks per Table 4-1.


My comment:

The changes proposed will be greater tolerances for assemblies with thermal heat sink planes than that with out.

My understanding of the exception was to allow for the physical properties of the thermal heat sink planes and the effects it has on normal processing of assemblies. The changes suggested in this notification will make soldering of assemblies with large thermal heat sink planes more difficult to achieve and actually has tighter requirements than assemblies without the thermal planes.

Is this change really accurate, if so, please let me know the proposed changes to the standard.

Michael Meanor
Director of Engineering

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