Circuit Board rework
The complexity of board assembly, limitations of the printed circuit board assembly process and the finite quality of electronic elements and materials all lead to the need to rework components on printed circuit boards. Rework, as defined by the industry IPC 7711 standard, is the act of reprocessing noncomplying articles, through the use of original or equivalent processing, in a manner that assures full compliance of the article with applicable drawings or specifications. In other words rework is the process of removing and replacing components due to any number of root causes with the outcome being that the printed circuit board is functioning as designed and comes with all of the applicable discrimination attributes as prior to the rework being performed.
Circuit board rework, in its truest sense, attempts to mimic the original manufacturing process so that the PCB meets the original manufacturing process standards. In this manner, the stresses on the board due to thermal and other environmental parameters are limited to those seen by the components in the original manufacturing process. With the added complexities of the board being previously exposed to a variety of operating conditions circuit board rework needs to take in to account these previous processes. For example, the laminate and solder mask may only be designed to be able to accept a finite amount of heat cycles. This means that there will only be a finite number of “tries” in circuit board rework as the thermal stress of the reflow cycles will limit the heat excursions. In addition, the same or superior materials should be used in the remanufacturing or printed circuit board rework process.
The need for circuit board rework coms from a variety of problems. For example, in the original assembly of the circuit boards, components can be misplaced in the feeder. This means that the devices will have to be desoldered, the site location prepped and the device re-soldered and inspected. In other cases devices can fail electrically or the interconnections be mechanically broken requiring circuit board rework to be performed to replace the device or resolder the interconnection. Whatever the case, circuit board rework requires that original specifications of the board be met. There are numerous challenges associated with modern printed circuit board rework including both logistic and technical issues.
The technical challenges of printed circuit board rework are too numerous to mention but several of the most challenging and often repeated ones are outlined below:
- BGA rework of very small footprint devices requiring a high degree of skill and great deal of experience is a challenge
- Ultra fine pitched part rework such as 0.4mm spaced leaded devices or ultra small package devices like 0201s is of concern
- Leadless devices with very small standoff distances requires fine process controls and ability to clean underneath low standoff heights and the ability to read x-ray images
- Handheld devices with shields around the RF transmission chips
- Underfilled devices requiring finesse so as not to scratch the solder mask or lift the pads
In addition to these technical challenges there are many logistical challenges associated with circuit board rework. In many cases the volume of rework is extensive for consumer oriented products. This means that pressure to get the “problem” fixed, especially with very long supply chains, is extensive. With nameplate holders in many cases in Europe, America or Japan it is a long distance between the warehouse with the defective product and the home base or factory of origin. Due to the timing pressures in order to get the factory performing the rework “up to speed” in many cases performing the rework back in the country of origin takes too long. In addition, the components may not be as readily available in the market where the rework is being performed as it may not be as plentiful as the country of manufacturing origin.
