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July 3, 2019

IPC SOIC Defect Question

IPC SOIC Defect Question
If solder touches the body of a ceramic or metal component it is classified as a defect, but NOT if it is a plastic body SOIC. Why is there a difference?

Reference: IPC-A-610, section 8.3.5.5 Flat Gull Wing Leads

D.O.

Expert Panel Responses

This condition originated with the large pads and small short leads as it was called in the beginning, circa 1980-90s. The physical leads were coming off from the bottom half of the component thickness. In Revision B of 610, this condition was identified as Low Profile Components (SOT and SOICs), the components with leads coming off the upper half of the component (QFPs and SOLs) were called High Profile Components as shown in the attached pictures.

With the amount of solder which was deposited on the pads with 6 and 8 mil stencils which were used and typical at the time and such small leads on SOT and SOIC the solder would climb to the top of the lead and contact the component body. The only way these component could be used at the time was to allow this condition to exist.

The following was Adapted from IPC-A-610 Rev B Section 10 Page 119
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This was also the criteria in Rev C circa 2000. In Rev D onward the committee rephrased the criteria to include the word Plastic Component in the definition and it has been that way ever since.

The other issue was the plating on the leads was tin/lead which allowed the solder to flow up the leads rather easily. There were no issues with the moisture entrapment with these component as they were not hermetically sealed, hence no problems were experienced with this condition. The only components which had lead seal issues were the ceramic components and this condition was not allowed on ceramic components.

I hope this explains the condition and if more is needed please don't hesitate to contact me at your convenience.

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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.

When solder touches a ceramic or metal component's body it could break the seal between the lead and the body allowing solder to sip through shorting out the component or allowing moisture to get in.

In the case of a plastic body it allows this to happen only for Class I since it is consumer electronics. I read that IPC did not have enough data to categorize it as a defect for Class 1, 2 & 3.

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Edithel Marietti
Senior Manufacturing Engineer
Northrop Grumman
Edithel is a chemical engineer with 20 year experience in manufacturing & process development for electronic contract manufacturers in US as well as some major OEM's. Involved in SMT, Reflow, Wave and other assembly operations entailing conformal coating and robotics.

Historically the reason for this difference is that the ceramic or glass-bodied parts have glass seals that may be damaged by the mechanical forces and/or thermal shock of direct contact with molten solder. In wave or hand soldering applications, this is certainly a concern, but in reflow, less so.

There is still the issue of increased mechanical stresses at the point where the lead exists the body, however, and if you have that much solder there are design and/or process issues that need to be addressed if possible.

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Fritz Byle
Process Engineer
Astronautics
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.

Ceramic components such as ceramic quad flat pack (CQFP) or other similar ceramic devices have a very low CTE (coefficient of thermal expansion) die material and are in most cases hermetically sealed to low-CTE lead-frame material such as Alloy 42 or Kovar.

Direct contact with molten solder or excessive rework cycles can result in a cohesive fracture or intermittent open interconnections between the die material and the lead-frame. In some cases these types of failures can only be detected after highly accelerated life test (HALT) or highly accelerated stress screen (HASS) testing.

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Carlos Bouras
General Manager
Nordson SELECT
Carlos Bouras is the General Manager of Nordson SELECT and has over 30 years of experience in the electronics manufacturing industry. Carlos's expertise is in process engineering, product development and manufacturing operations. For the past 15 years Carlos has focused specifically on automated assembly issues and is the holder of several US patents for non-contact dispensing and precision dispensing of adhesives for the packaging of microprocessor devices.

The issue with "IPC SOIC Defect" relative to if solder touches the body of a Metal, Ceramic, or Plastic component :
  1. Metal is electrically conductive hence a defect as may cause an electrical short.
  2. Ceramic is susceptible to heat via subsequent internal cracking, as well as etching of any glass fillets possibly creating an electrical short , at least for space.
  3. Plastics are not conductive so if solder touches body will not cause electrical shorts.


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Mark Northrup
VP of Advanced Technical Operations
IEC Electronics
Mark has over 25 years' experience in electronics fabrication, quality and reliability while working for IEC Electronics, GE, Motorola, ORS, etc. He has most recently established IEC Electronics Analysis and Testing Laboratories (IATL), LLC in Albuquerque, NM for electronics and material analysis testing in the military, medical, and industrial industries. His area of expertise includes PCB, PCBA, components, analytical and electrical analysis techniques.