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October 28, 2013

IPC-A-610 Solder Joint Acceptability Question

Per IPC-A-610, figure 5-1, solder connection angle shall not exceed 90 degrees unless there is solder mask on the pad, or you are soldering to a high voltage application. This is the only place this is mentioned. Where other defects are called out according to Class; Acceptable, Process Indicator or Defect, this condition is not.

Per IPC-A-610 1.4.1.6, conditions that are not specified as defective or process indicators may be considered acceptable.  

I recently had an operator question me on this. I feel that since this issue is not clearly call it out as a defect, it is acceptable. Our team looked at the verbiage above figure 5-1, and said that since it says we shall not have greater than 90 degree wetting, we need to rework the joint.  

Would you please clarify this issue.

S.P.

Experts Comments

I think you've misinterpreted the section.

First, don't forget that in section 1.2 there is a bold, italicized statement that says, "In the case of a discrepancy, the description or written criteria always takes precedence over the illustrations." In essence, you can ignore the pictures and go with the text of the standard throughout the standard.   Second, figure 5-1 shows examples of acceptable connections. Notice that only one of the pictures has solder on the land.  

The text doesn't say that the connection is only acceptable if there is solder mask on the pad.  

The text lays out the criteria in "legal" terms. It says that no connection can be over 90 degrees... EXCEPT if the solder connection first wets the entire available, solderable area on the land, and THEN goes past 90 degrees. It goes on to say that the connection MAY exceed 90 degrees when the connection is created by the solder extending over the edge of the solderable termination area OR solder resist.  

Just because the solder connection goes beyond 90 degrees does not make it a defect condition.  

The concern is that if the solder doesn't wet all the way to the edge of the pad, it may curl under the solder connection and not wet to the land at all.  

Carefully examine the connection using the magnification called out in table 1-2. If there is proper wetting all the way to the edge of the solderable area, and the solder does not violate minimum electrical clearance, then it is not a defect.
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Kris Roberson
Manager of Assembly Technology
IPC
Kris Roberson has experience as a machine operator, machine and engineering technician and process engineer for companies including Motorola, and US Robotics. Kris is certified as an Master Instructor in IPC-7711 / 7721, IPC A-610 and IPC J-STD 001.
You state in your question:  

"Our team looked at the verbiage above figure 5-1, and said that since it says we shall not have greater than 90 degree wetting, we need to rework the joint."

You need to read the entire paragraph related to figure 5-1, which also includes an exception, which states "... the solder connection to a termination may exhibit a wetting angle exceeding 90degrees. Figure5-1 (C, D), when it is created by the solder contour extending over the edge of the solderable termination area or solder resists." 

Many times you may have a solder connection which wets the lead perfectly and looks like a Hersey Kiss but is somewhat excessive on the pad area. When this condition exists the wetting angle is greater than 90 degrees and the condition is still acceptable, reference Figure 5-2 #1 for an example of a joint which could somewhat overhang the pad and still be acceptable.
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Leo Lambert
Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.
IPC-A-610E Clause 1.4 answers this question.

"This document provides acceptance criteria for completed electronic assemblies. Where a requirement is presented that cannot be defined by the acceptable, process indicator, and defect conditions, the word "shall" is used to identify the requirement. The word "shall" in this document invokes a requirement for manufacturers of all classes or product, and failure to comply with the requirement is a noncompliance to this standard."
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Jack Crawford
Director - Certification & Assembly Technology
IPC
Mr. Crawford is Director of Certification and Assembly Technology for IPC. He is technical liaison to the IPC committees that maintain critical industry standards and has presented numerous papers internationally.
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