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What information is available on the assembly process for BGA ?
  
  Although a lot of parts are being processed, only limited information is available. The SMART Group has produced a BGA report with all proceeds from the sale of the report going to charity. For a copy of this report, contact the SMART Group, tel: 01494 465217. Two videos on BGA are also available from EPS, see video listing.  
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  There may be advantages with BGA but isn't the cost of parts higher ?  
  There is a wide range of articles written on the subject for applications in the commercial sector and in telecommunications. Tests have been conducted on temperature cycling, vibration and flexture testing. A bibliography is available from the SMART Group, Tel: (+44) 01494 465217  
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  The use of BGA is relatively new, what reliability data is available ?  
  There is a wide range of articles written on the subject for applications in the commercial sector and in telecommunications. Tests have been conducted on temperature cycling, vibration and flexture testing. A bibliography is available from the SMART Group, Tel: (+44) 01494 465217  
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  I work in quality engineering, how can I inspect BGA solder joints ?  
  Because the solder connection is under the device, you cannot inspect the part using any traditional means. If joints are to be inspected, then some form of X-ray inspection equipment will be required. As any form of X-ray will still only show a solid solder ball, special design rules are required for the assembly.  
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  I understand that BGA devices are very prone to cracking during reflow and rework. Is this like QFP popcorn ?  
  Yes, it is generally known as the "popcorn" effect. If moisture is in the package during reflow or rework it may cause pressure to form in the device. This then causes delamination between the moulding and fibreglass substrate. As the pressure is relieved, you can hear a pop! Control in the manufacturing process can eliminate the problem.  
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  What are the advantages of Ball Grid Array technology to the design and assembly engineer ?  
  Generally speaking, components are using finer and finer pitches, well below 0.020". This increases the difficulty in tracking the boad design and increases the need for circuitry below 0.006". Both have an effect on board price. The assembly engineer is faced with high proability of poor lead quality and the need for higher levels of optical inspection and correction on assembly equipment. With BGA, the pitch actually increases to between 0.050-0.060", but still providing over 300 termination points on the package. Would you rather handle 0.020" or 0.006" pitch? The process yield reported by BGA users is far higher than with fine pitch. BGA technology also allows users with lower specification for assembly equipment to use the technology. EPS have a whole range of BGA training products just call for further information.  
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Bob Willis, Process Engineering Consultant Electronic Presentation Services
2 Fourth Avenue Chelmsford Essex CM1 4HA England Tel: (44) 01245 351502 Fax: (44) 01245 496123
Email: bob@bobwillis.co.uk