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March 25, 2014

IPC 610 Class 3 with Missing Non-functional BGA Pads

We have a board assembly that must be built to IPC 610 Class 3. On a few boards it has been necessary to remove and replace a BGA packaged part.

Three pins on this BGA part are non-functional and have no connects. Frequently, those three non-functional pads are lifted off the board during BGA part removal. The pads are not replaced prior to installation of the new BGA part.

Can these boards still be said to meet Class 3 with these 3 non-functional pads missing on the PCB?

If not, is there anything we can do to repair these boards to meet Class 3?

A.M.

Experts Comments

There are a couple of things to consider.  

The first thing is, what do the customer drawings say? If the drawings state that all of the pads, functional or not, have to be properly attached to the board, then that is what needs to happen. (See IPC-A-610E, 1.4.1 "In the event of conflict, the following order of precedence applies: 1. Procurement as agreed and documented between customer and supplier. 2. Master drawing or master assembly drawing reflecting the customer’s detailed requirements. 3. When invoked by the customer or per contractual agreement, IPC-A-610.")  

Second, look at the definition of “Acceptable” and “Defect” condition.

IPC-A-610E 1.4.1.2 Acceptable Condition
This characteristic indicates a condition that, while not necessarily perfect, will maintain the integrity and reliability of the assembly in its service environment.  

IPC-A-610E 1.4.1.3 Defect Condition
A defect is a condition that may be insufficient to ensure the form, fit or function of the assembly in its end use environment. Defect conditions shall be dispositioned by the manufacturer based on design, service, and customer requirements. Disposition may be to rework, repair, scrap, or use as is. Repair or "‘use as is"’ may require customer concurrence.  

In both of those conditions the key is the integrity, reliability, and function of the assembly in the service environment. Will the missing, non-functional pads cause a reliability of functional issue within the intended life of the product? If not, then the missing pads may not be a defect.  

As a caveat to the above, look at the last line of the defect condition. “…’use as is’ may require customer concurrence.” Especially for a class 3 assembly, the customer needs to know about the condition and give a decision as to whether the missing pads can be used as is or must be repaired.  

In answer to your final question about repairing the boards, if you do need to repair the boards, there are a couple of procedures in the IPC-7721B - Modification and Repair document which are classed as "High" level of conformance. A "high" level of conformance means that the repair is as close as possible to the original form, fit, and function of the original assembly. A Class 3 repair should be done to the highest level of conformance available.  

The specific procedure you would be interested in are the 4.7.3 "Surface Mount, BGA Pad Repair, Film Adhesive Method". There are other methods in the IPC-7721B which could easily be modified to be used on a nonfunctional BGA land.
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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.
From an inspection standpoint, no, I don’t believe that boards with the non-functional lands meet the intent of the specification, since solder joints that are intended to be there are not. The absence of those joints can have an impact on the reliability of the part. Heat transfer may be affected and thermal cycle reliability could be reduced if the balls are in or near the outer row.

Replacement of the missing lands is allowed, and the methods are covered in the IPC-7711B/7721B specification.
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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.
If you are missing the pads (pulled in the rework process), this is a defect regardless of functionality of the board (pads being used or not). From your description, if this happens in the part removal process, that means that
  • The reflow profile for component removal is not appropriate for the board construction
  • Those particular pads have probably heavy ground planes and no relief so they require higher temperatures than the rest to get them soldered/unsoldered
However, the root cause of the problem is improper reflow the first time (initial pick and place and reflow) and this is what it needs fixed immediately so rework will be avoided.

Should rework be needed, a proper profile on the equipment has to be developed so the operation is safe.

Last, if the pads are pulled, a customer approval for repair is necessary in order to fix them. The repair can be performed by trained personnel.
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Georgian Simion
Engineering and Operations Management
Independent Consultant
Georgian Simion is an independent consultant with 20+ years in electronics manufacturing engineering and operations.
Contact me at georgiansimion@yahoo.com.
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