October 15, 2019
We all know that communication is fundamental to organizational success. We realize its importance — to build relationships, reduce errors, facilitate innovation and ensure transparency — are a few benefits that come to mind, yet many still struggle to get their team moving in the same direction.
If you think the task is difficult enough to achieve within your organization, try getting all your suppliers on the same page.
“Effective supply chain communication is essential to achieving a quality end product,” said Crystal Vanderpan, a principal engineer with UL’s Consumer Electronics division.
Vanderpan, who works primarily with printed circuit boards (PCBs), has witnessed the after-effects of PCB products that initially passed testing only to fail at a later date. Bare board warping, layer-to-layer delamination and/or the introduction of thermal-stress induced cracks are a few of the quality issues she has observed.
“Any of these failures can seriously disrupt circuit integrity during the end product manufacturing stage and may not be detected until after the product is in the field,” she said.
Vanderpan stressed that new materials might require additional testing to establish compliance with component and end-product requirements.
“Current PCB assembly processes include repeated soldering operations and surface mount reflow with multiple cycles at higher lead-free temperatures,” she said. “Boards may also be exposed to combinations of wave soldering and hand soldering of special components that could damage PCBs or mounted devices. The risk of damage from repeated soldering requires flammability, conductor bonding and/or other characteristics to be re-evaluated.”
An expense that many manufacturers do not want to incur, as any delay in getting their product to market costs both time and money.
“Preselection is, therefore, an extremely valuable tool for both product designers and component suppliers, providing confidence in product performance and safety compliance up and down the supply chain,” Vanderpan said.
“Additionally, when you use preselection test data from an independent source, the predictability of the end-product evaluation is enhanced, product lead-time shortened, and the cost of performance testing and safety compliance reduced.”
Representative of the assembly process
The UL Standard for printed wiring boards (UL 796) requires the thermal stress evaluation (solder limit preconditioning) to be representative of the assembly process, however, as Vanderpan noted, it’s not possible to test the numerous soldering operations used during assembly.
“Board fabricators may specify the solder limit conditions, but they continue to follow the practice of simulating the assembly process with a solder float test.”
Vanderpan pointed out that the solder float test preconditions the board at one maximum temperature for a specified time only, warning that “the test is not representative of a cumulative soldering process with multiple steps.”
Conversations with the board suppliers to coordinate the assembly process is very important. Collaboration throughout the supply chain will reduce the risk of delays.
Currently, the IPC thermal stress test method, TM-650 2.6.27, uses standardized temperature profiles to establish the survivability of boards. These standardized settings allow PCB fabricators to specify the maximum/peak reflow temperature and the number of soldering cycles the PCB will be exposed to during assembly.
UL is proposing to add these standardized survivability methods to UL796 as an alternative to solder floats. Acceptable testing will then result in PCB Recognition with the standardized solder limits.
Are you interested in learning more about PCB preselection? We can help you reduce testing by offering standardized thermal stress preconditioning to simulate the assembly processes. You can search UL’s Product IQ® Database to view the recognized solder limits.