|Ask the Experts|
July 20, 2020
Depaneling circuit board that contain BGA components
Are there any special requirements for depaneling or V-scoring to separate paneled circuit board if they contain BGA components. What are the best/safest methods for depaneling circuit boards that have BGA components?
|Expert Panel Responses|
Depending on the proximity of the BGA devices to the edge of the PWB, it is normally prudent to minimize any external stresses to the devices. Proper support of the array is paramount in order to prevent pad cratering type defects or fracturing the solder joints. Routing is the preferred method.
S T and S Testing and Analysis
All components and their interconnects should be protected from the stress that can be created by depaneling processes that flex or shear the PCB substrate. Small ceramic capacitors, BGA's, LGA's, QFN's, or any other components with minimal interconnects are particularly susceptible to damage.
If the components are near the PCB edge, then de-panelizing with a router would be preferred. If you must use a shearing process, then tooling should be used to isolate the stress and prevent PCB flex.
Principal Product Engineer
Benchmark Electronics, Inc.
Rotary-wheel (pizza-cutter) type depaneling can be effective. If this is used strain-gaging is commonly employed to ensure that any forces generated during the operation are not sufficiently large to cause damage to area array (BGA, CGA, etc.) package solder joints. In general, I prefer this type of depaneling. Of course, the board must be designed to accommodate pizza-cutter depanelization.
The best method is UV Laser depanelization.
Director of Quality / CLSSMBB
The component density on pcbs continues to increase with 2000, 3000 or more placements becoming the norm. Depaneling pcbs becomes more critical with complex boards, which have tighter pitches, more layers and increasing thickness.
Depaneling introduces mechanical stress on a pcb that can cause premature electrical failure, or worse cause intermittent operation. The primary pcb problem manifested from the external forces of depaneling is edge delamination. PCB layer delamination can expose the board to moisture, fluids and surface variations.
Of the potential problems caused by delamination - surface variations present the most problems for BGAs. Surface variations change the coplanarity of the BGA putting undue tensile strain on the ball to pad solder joint. This coupled with the "normal condition parameters" can have adverse effects on product performance and life. Delaminations are irreversible under normal circumstances, IPC 7711 and 7721 does offer a repair procedure but this is costly and adds considerable time to the build cycle.
The key is to minimize stress during depanleing. Laser cutting and routing are the least traumatic for depaneling pcbs with BGAs, and it reduces/eliminates delaminations.
It always helps if the BGAs are kept away from the areas where the depanel is taking place. We use a "pizza cutter" type of blade to depanel v-score, and a router for route tabs. Both of those impart very low stress to the PCB.Kelly Atay, Sunstone Circuits
Random or intermittent opens can occur within BGA or micro-BGA components during the de-paneling process if the devices are located in close proximity to the edge of an individual circuit. Board flexure during the de-paneling process exposes the outer edges of the BGA device, and especially the perimeter balls and corner balls, to the highest levels of stress since an uneven fracture distribution is indicative of localized mechanical stress.
V-scoring typically leaves 1/3 of the board intact which in most cases is manually broken over a sharp edge resulting in stress within the board and the board-BGA device interface. De-paneling fixtures should be designed to fully support the board on both sides of the score line to minimize these stresses.
A 'pizza cutter' type de-paneling wheel can also induce stress on a BGA device if they are too close to the edge of the circuit board. The safest de-paneling method is to use a router to separate individual circuit which is typically slower than breaking or cutting, but is the best option to ensure integrity of the board-BGA interface.
A similar intermittent BGA fracture failure can occur during in-circuit test if the board does not seat properly in the test fixture causing an operator to repeatedly reactive the test procedure resulting in unnecessary fixture recycling putting additional mechanical stress on the board. In both cases it is recommended to implement strain gage testing to provide real-time monitoring of unidirectional strain levels exerted during the de-paneling and in-circuit test processes.
Using an automated router with a saw blade does not create much stress on these components however a test can be performed on the board itself during sawing to make sure no stress is causing any failure to the components.Tom Herndon, SCHUNK Electronic Solutions
If the components are very close to the edge special fixture can be created as well to help avoid any damage.
Each depanelization process has its own risks. That is why when you design the panel. be mindful of the technical capabilities and process flow to understand the risks.
There is no standard restriction for boards with BGAs not being designed with V score for depanelization. The process itself has to be safe and sound - good equipment, applicable procedures, mindful operators.
Engineering and Operations Management
Laser Depaneling is by far the most gentle method for depaneling a circuit boards. It is completely free of any mechanical stress which adversely can affect solder joints or sensitive components. In fact, you can place components much closer the edge of the circuit board when laser is used for depaneling, maximizing the useable real estate on the board.Stephan Schmidt, LPKF Laser & Electronics
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