This disclosure relates generally to manufacturing, and, more particularly to methods for manufacturing reliable medical devices by controlling vendor shipments of components or subassemblies.
Reducing the amount of dangerous or hazardous materials in our environment is a laudable goal. Some industries generate more of these materials than others, of course. For example, the electronics industry has long used the material Lead as a common material for producing low-cost electronic parts, due to special qualities of Lead or Lead mixtures such as a low melting point, malleability, durability, and the fact that Lead is electrically conductive. Lead is also a significant component of Tin-Lead solder, a very common solder used for producing electrical components such as printed circuit boards.
Unfortunately, Lead is a hazardous substance and oftentimes leaches into the environment from improperly disposed electronic devices. In response to this problem, there is a world-wide effort to reduce the amount of Lead and other hazardous substances in electronic devices.
As an alternative to Lead, many producers have created some component structures, such as pads and other connections, out of Tin, solely, rather than the Tin-Lead mixture. Using Tin-only structures created new problems. Specifically, when Tin is used without Lead, some Tin structures produce “whisker” defects that increase in severity over time. Metal whiskers are a metallurgical crystalline phenomenon where filiform or spiky metal “hairs” grow from the metal surface. Tin whiskers are believed to occur when the underlying Tin structure relieves internal crystalline stresses, such as thermal stresses, which are exacerbated by high temperature and high humidity. Tin whiskers are especially problematic in components having small inter-structure distances. With reference to
Embodiments of the invention address these and other limitations of the prior art.
For components having critical specifications 210, further categorizations may exist. Typically when a manufacturer orders a component or sub-assembly from a vendor or supplier, the specific component is selected based on published specifications by the vendor. For example, a vendor that sells batteries may publish specifications about the batteries, so that a manufacturer can select the correct product to meet the manufacturer's needs. The battery specifications may include, for example, material type, physical size, voltage, storage capacity, and the number of cycles that can be recharged. The manufacturer selects the appropriate battery, based on the specifications, then assembles the selected battery into the manufactured product.
One problem with published specifications is that they may not match the actual specifications of their component product. This is especially true when the component product is manufactured differently than when the specifications were generated. In the battery example given above, the battery producer may change raw material suppliers to achieve a better price, which may have a detrimental effect on the number of recharging cycles that the new batter can withstand. Unless the vendor tests every specification every time a production change is made, the specifications may, in fact, not match the actual performance of the product as delivered. In this instance, the actual battery shipped under the old specifications may not meet the specified number of recharge cycles. Usually a vendor rates its components at “minimum” specifications, with a conservative minimum number that the vast majority, if not all, of the components should meet. For example, if a battery producer tests the number of recharge cycles for a significant number of batteries in a specific lot of batteries, and the lowest number of recharge cycles was 1581, a vendor of the batteries may state in the published specifications that the maximum number of recharge cycles is 1500.
As described above, Lead is gradually being removed as a material used in the production of electronic components and devices. Generally the vendors of such devices will advertise or publish the fact that their components are made without Lead. There is an industry reluctance, however, to change part numbers of components. Thus, a manufacturer who receives components or assemblies from a vendor may not receive specific notice that the producer has changed an underlying component, such as a part number change, absent the manufacturer searching for a published notice to that effect. In other words, a manufacturer may not be informed that a producer or vendor has substituted a component or sub-assembly that previously contained Lead with a newer, Lead-free part, because the vendor may not change the component part number but only change the part specifications. Because most electrical products include a multitude of parts, and because it is unlikely that the manufacturer is continuously researching the vendor specifications for each of the multitude of parts, the manufacturer may never know that a component or part no longer contains Lead. This is especially true because most vendors consider a Lead-free product to at least equal in form, fit, and function to a product that contains Lead, and generally believe that all manufacturers would rather receive the Lead-free part. Thus, in some cases, vendors substitute Lead-free parts for parts that previously contained Lead without notifying their own customers. As described above, however, substituting Tin parts for parts that previously contained a Tin-Lead mixture can lead to failure of a device manufactured with the Tin parts.
Therefore, embodiments of the invention include an inspection step inserted into the manufacturing process. Specifically, for components having critical specifications, described below, embodiments of the invention include a process where such critical components are tested, either by the medical device manufacturer or by the vendor to ensure that the components meet the manufacturer's specifications, without regard to the published specifications of the components. With reference back to
In this simplified illustration of
The diagram of
Embodiments of the invention take steps to ensure that components originally selected by a medical device manufacturer 310 are not substituted with unsatisfactory components. A process 311 is performed by the medical device manufacturer 310, the details of which are given below, to ensure that only desirable components and sub-assemblies are used in the medical device 200.
With reference to
In the process 430, a particular gap distance is determined by the medical device manufacturer for each of the at-risk components on the list created in the process 420. Different component types on the list made in the process 430 may have different gap distances. For example a semiconductor component may have a particular critical gap distance while connector components have a different critical gap distance. Thus, in the process 430, particular qualifications are created for each type of component on the list created in the process 420. Further, there may be multiple qualifications for each type of component. Thus, a medical device manufacturer may specify that semiconductor components having an air gap of greater than 0.35 mm are acceptable if made out of a first material, but not acceptable if made out of a second material. Detailed examples appear below. The list created as a result of the process 420 is termed a “watch list” because the components on the list are watched by the medical device manufacturer to be sure that they satisfy their minimum performance requirements.
In the process 440, the components on the watch list created in the process 420 are tested to be sure that each component satisfies the minimum component requirements set by the medical device manufacturer. In some instances the testing may be performed by the medical device manufacturer. In other instances the vendor may perform the test, then generate data or evidence for the medical device manufacturer that proves, to the medical device manufacturer's satisfaction, that the components pass the standards set by the medical device manufacturer. The tests may be sample or lot tests only, such as testing two components out of a shipment of five-hundred, or one in one-hundred.
Finally, in a process 450, the medical device is assembled using only those components that passed the test performed in the process 440, or those components that were not on the list of at-risk components. Thus, manufacturing a medical device using these processes minimizes the risk that the medical device will fail for the failure condition for which the tests were established.
In a process 525, the sub-assemblies and components are received from vendors. A process 530 determines if all components that could fail have been analyzed against the criteria, which for the first time through is necessarily exited in the NO direction. When the process 530 is exited in the NO direction, the components are analyzed in a process 532. As described above, the tests can be performed by the medical device manufacturer or by the vendor of the particular component. Specific to the Tin whisker fail condition, one method to implement the testing process 532 is to examine metallurgical makeup of the metal structures within the components. One method to determine metal content is to use X-Ray Fluorescence (XRF), which uses spectroscopy. An XRF analyzer typically generates a numerical display that can be read by the operator to ensure that the metal is made from at least (or less than) a certain percentage of the measured component. Another test method is to use a Scanning Electron Microscope, but may not be preferred because it is relatively more expensive than using XRF.
A process 540 determines if all of the components have been checked against the criteria established in the process 512. If some of the components did not pass the analysis, they are rejected in the process 542. Rejection can take the form of instructing a vendor to not ship a component that cannot pass the criteria, or refusing to accept delivery of a component that fails a criteria analysis. In some embodiments only certain components of a larger shipment may be spot checked for criteria compliance. After all of the components have satisfactorily passed the analysis, the medical device is assembled in the process 544.
Some of the spacing thresholds may be based on a minimum distance between structures of the components, for example pin structures. Some threshold are based on an absolute minimum distance between pins, while other thresholds are based on average pin distance, also referred to as pitch or air gap thresholds. Other embodiments of the invention may use other spacing thresholds.
After the spacing thresholds are established in the process 610, the components including metal are received from the vendor or vendors in a process 620. Additionally received in the process 620 are assurances that the received components are of a stated metallurgical composition. These assurances may be made by product specifications, advertising material, or other written or oral assurances. The assurances may also be in the form of test data provided by the vendor of the components containing metal.
If the components received in the process 620 include spacing gaps beneath the threshold established in the process 610, then a metallurgical analysis is performed. The analysis can include XRF analysis, SEM analysis, or examining metallurgical analysis data that was produced by the vendor. Finally, in the process 640, only components that have satisfactorily passed the established tests are assembled into the final medical device.
The above description outlines general processes according to embodiments of the invention, and how to minimize the likelihood of assembling a medical device that is prone to failure for reasons of a particular defect. Described below is a detailed example of how the embodiments of the invention can be used to generate a medical device with a minimum or reduced likelihood of failing due to metal whiskering.
Flex circuits are those circuits that, as compared to rigid structures, may need to be flexed, moved, or manipulated during assembly of the medical device. Some flex circuits include exposed traces, which may or may not be covered by another material. In this example components for use in the flex circuits are broken into acceptance divisions based on preference for use within the medical device. For example, with regard to circuits that include exposed traces, there are particular types of components that are in a preferred division 710, some that are permitted but not preferred 720, some that are conditionally allowed 730, and those that are not allowed 740.
The components most preferred for the flex circuits include exposed traces made from (or containing) Lead or metals found in iNemi Category 1. The International Electronics Manufacturing Initiative (iNEMI) is an organization dedicated to global electronics manufacturing. Also within the preferred division 710 are components having exposed traces made from iNemi Category 2 metals that have been tested, using the methods described above, for metallurgical makeup, provided that such traces have an air gap of greater than or equal to 1.0 mm.
The permitted division 720 of flex circuits allows for the use of untested Category 2 metals, but only if such metals are in exposed traces that have greater than or equal to a 5.0 mm air gap. This is because, given their untested status, such exposed traces may in fact contain Tin, but having such a relatively large air gap minimizes the likelihood that Tin whiskers will be problematic. Further, iNemi Category 3 metals may be used in this division, but again only for exposed traces having an air gap of greater than or equal to 5.0 mm.
The conditionally allowed division 730 includes flex circuits having exposed traces made from Category 2 metals having an air gap of between 1.0 mm and 5.0 mm. Conditional allowance means that such parts are placed on a list for design-level mitigation of the Tin whisker failure problem. Each conditionally allowed component is analyzed for risk of failure and may include a higher level of scrutiny than other components before being allowed to be produced into the medical device. In some instances, future generations of product may be re-designed to accommodate or mitigate the use of conditionally allowed components. For example if a particular conditionally allowed component is redundant, or can be protected by applying a conformal coating, it may be conditionally allowed. Other factors of design level mitigation may include insulating barriers or including electrically isolated separation pins or traces. Additionally in the conditionally allowed division 730 are those flex circuits that include exposed traces made from Category 3 metals having an air gap between 1.0 mm and 5.0 mm in components where it was decided that such components are not critical. Typically critical components are ones that are more important to the function of the device. If a part is not critical, it is a less-important part, which is why the Category 3 materials for this size air gap can be conditionally allowed.
Conversely, if the exposed trace is formed from a Category 3 metal having between 1.0 and 5.0 mm air gap in a component deemed to be a critical component, i.e., one in whose failure would cause an important function to not work then such a component is placed in the division 730 and not allowed to be assembled into the medical device. Further components falling in the not allowed division 740 include Category 2 and Category 3 metals having less than a 1.0 mm air gap.
Using the divisions 710, 720, 730, and 740 of
If the medical device manufacturer deems that components are unacceptable for assembly into the medical device, such components may be rejected by the medical device manufacturer before they are even shipped by the vendor. In other cases the purchasing contract may be written such that acceptance of the goods is “subject to” the components passing the specified tests, and components not passing the tests are not legally “accepted.” In yet other cases, the medical device manufacturer may be able to return non-conforming parts to the vendor, even after acceptance, based on other agreements or depending on the trade.
In some instances non-conforming goods may be put through a mitigation process to convert them into conforming goods. For example, a component having a high Tin content structure may be mitigated by dipping such a component in a solder that includes Lead. Doing so minimizes the probability of developing Tin whiskering. If the component can be modified by such a process into one that is acceptable for the medical device manufacturer, then the modified component may be assembled into the medical device.
Some embodiments of the invention have been described above, and in addition, some specific details are shown for purposes of illustrating the inventive principles. However, numerous other arrangements may be devised in accordance with the inventive principles of this patent disclosure. Further, well known processes have not been described in detail in order not to obscure the invention. Thus, while the invention is described in conjunction with the specific embodiments illustrated in the drawings, it is not limited to these embodiments or drawings. Rather, the invention is intended to cover alternatives, modifications, and equivalents that come within the scope and spirit of the inventive principles set out in the appended claims.