Rework & Repair – No Substitute for Experienced Staff

■ Test Boards used in the Rework Experience.

■ Test Boards used in the Rework Experience.

The rework and repair of printed board assemblies need special skills and equipment if it is going to be conducted in a professional manner. There are many very skilled staff who repair boards on a daily basis using the most sophisticated tools or relying on tricks of the trade with basic equipment. Rework can be conducted without impacting the reliability of a product and has been demonstrated in the past provided it is done correctly. Many people think that rework reliability is based on just the solder joints; however, if we look at potential failure modes there are also surrounding components and the printed board substrate. Any company in the electronics industry, particularly contract manufacturers, should have a world class capability with the tools and skills well defined to meet current and future customer challenges.

Meet the Rework Experience Team at SMT Nuremberg 2016 and Take the Rework Challenge.

Many of the component removal and replacement methods are outlined in IPC 7711/7721 and there are specialist training providers who teach operators these techniques so a product can be repair on site or in the field. In reality, however, most product failures are returned to base for component level replacement, particularly fine pitch and area array products. It should be fully understood by management that some soldering technicians do not make great repairers. It’s not that they have a lack of interest but simply some take more easily to rework and have a real pride in perfection. The author has been asked to train staff in PCB track level and component level repairs; on many cases it was clear that they just did not have the patience, this leads to frustration and poor results.

For the first time we have created the opportunity to experience all the most demanding rework challenges in the industry with our Rework Experience exhibition feature area at SMT Germany 26-28th April. Visitors can watch experts rework boards featuring area array, fine pitch, underfill and conformally coated boards and ask their advice on your repair challenge. Our latest Experience feature area will provide procedures and practical hands support for your biggest challenges in a real live environment plus the opportunity to win IPC standards and guidance documents. We have been organising special feature areas for many years but this is the first based on rework, repair and Inspection with members of IPC.

We have been organising special feature areas for many years but this is the first based on rework, repair and Inspection with members of IPC.

IPC have been running their Hand Soldering Challenge successfully for many years, a competition to find the best hand soldering operator using a through hole and surface mount test board. The author’s concept was to design a simple test board incorporating fine pitch, area array and bottom mounted components to further test an operator’s skills. The board design below features components that are widely used in industry today and in many companies the skills to rework these parts is a necessity. The board used in the Experience is 1.6mm laminate with gold over nickel surface finish. The design could easily be adapted with more layers to increase the thermal demand and the challenge. However, when a process for rework is considered or defined during New Product Introduction (NPI) the difference in pre-heat, reflow and dwell time should have been defined for a specific rework station before being used with advanced component design comes other challenges to production staff, the removal of conformal coating before rework and the possibility of underfill or component staking being used on area array components to enhance operational reliability. A world class repair facility and staff should be able to deal with any combination of materials and components.

The aim of the challenge is the opportunity to rework and repair one board which features one Plastic Quad Flat Pack, Plastic Ball Grid Array, Chip Scale Package and Quad Flat No Lead packages. The rework operations are conducted in line with accepted standards and meet the inspection criteria in IPC 610 class 3. The time taken to finish the exercise is also important in the judging process. We hope to incorporate the use of convection and IR rework systems typically used in industry but allow participants to use the tools, methods and materials of their choice to meet the inspection criteria defined in IPC 610 class 3. If we look at the four component types, they can be soldered to the boards and reworked using different techniques. In many companies this is defined by engineers; however, if a better and faster technique becomes available the process should be re-examined. It is also the case that not all companies have the correct tools but this is where the experience of the staff is invaluable.

■ One option for replacing PQFP packages or PBGAs is dip paste, a product developed for package on package assembly but has been proven very successful for standard rework.

■ One option for replacing PQFP packages or PBGAs is dip paste, a product developed for package on package assembly but has been proven very successful for standard rework.

The following are methods used in the industry to solder or rework parts. The methods in a company may vary but it is always worth trying new techniques to enhance skills and possibly improve the process:

PLASTIC QUAD FLAT PACK

• Individual leads are soldered manually with wire and a soldering iron

• Leads are drag soldered using liquid flux and solder wire

• Dip solder paste is used on the leads then the joints are reflowed with IR or convection

PLASTIC BALL GRID ARRAY & CHIP SCALE PACKAGE

• Solder paste is applied to the substrate, component placed & reflowed

• Flux gel is applied to the PCB or solder spheres, component placed & reflowed

• BGA is dipped into dip solder paste, placed & reflowed

• Print paste with plastic stencil, place part and reflow

Rework of QFN devices often use a mini stencil to print standard lead-free paste on to the package terminations before placing the part and reflowing in place:

QUAD FLAT NO LEAD

• Solder paste is applied to the substrate, component placed & reflowed

• Solder paste is printed on to QFN, component placed & reflowed

• Solder paste is printed on to QFN & reflowed. Gel flux on QFN pads, placed & reflowed

For further information on the BGA, Fine Pitch, Underfill & Conformal Coating Experience at SMT Germany 26-28th April:

www.mesago.de/en/SMT/For_exhibitors/Rework_Experience_Area/index.htm

If you would like to feature materials and equipment in the Experience please contact Lars Wallin:

LarsWallin@ipc.org

For a list of the materials and equipment that may be considered when setting up your onsite advanced rework center email Bob Willis:

bob@bobwillis.co.uk

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