可靠度證明試驗(Reliability Demonstration Test)

可靠度證明試驗(Reliability Demonstration Test)

• Reliability Demonstration Tests (RDT): Often used to demonstrate if the product reliability can meet the requirement. For this type of test design, four methods are supported in Weibull++:
  • Parametric Binomial: Used when the test duration is different from the time of the required reliability. An underlying distribution should be assumed.
  • Non-Parametric Binomial: No distribution assumption is needed for this test design method. It can be used for one shot devices.
  • Exponential Chi-Squared: Designed for exponential failure time.
  • Non-Parametric Bayesian: Integrated Bayesian theory with the traditional non-parametric binomial method.
• Expected Failure Times Plot: Can help the engineer determine the expected test duration when the total sample size is known and the allowed number of failures is given.
• Difference Detection Matrix: Can help the engineer design a test to compare the BX% life or mean life of two different designs/products.
• Simulation: Simulation can be used to help the engineer determine the sample size, test duration or expected number of failures in a test. To determine these variables, analytical methods need to make assumptions such as the distribution of model parameters. The simulation method does not need any assumptions. Therefore, it is more accurate than the analytical method, especially when the sample size is small.

Readers may also be interested in test design methods for quantitative accelerated life tests. That topic is discussed in the Accelerated Life Testing Reference.

http://reliawiki.org/index.php/Reliability_Test_Design#Reliability_Demonstration_Tests

可靠度壽命試驗(MTBF)

MTBF(Mean Time Between Failures-MTBF)

以加速壽命試驗模式進行產品壽命驗證已行之有年，最具代表性之溫度加速壽命試驗
為Arrhenius Model(見圖一)，有關熱-金屬疲勞壽命則以Coffin-Manson Model為主(見圖二)，就無鉛焊點之壽命評估而言多數國外大廠均採用溫度循環應力模式(Coffin-Manson Model)作為PCBA焊點可靠度壽命評估。

 對於組成系統後之產品壽命評估則以下列三種為主要模式，其優缺點簡述如下：

 壽命預測(Prediction) 

常用方法：通常以零件參數或由零件量測所得之溫度作為基礎資訊，將此資訊輸入分析軟體後即可計算出產品之MTBF(Parts count or Parts stress) 
優點：可以快速得到MTBF數值 
缺點：零件規格變化快速，預測方法並未隨著零件或產品的演進而演進，且零件一旦組成系統時，線路阻抗因素、電壓/電流因素等均無法模擬，因此其所預估出之壽命代表性令人質疑。

   可靠度證明試驗(Reliability Demonstration Test) 
常用方法：高溫加速模式(Arrhenius model- Equation 1) 
優點：實驗結果+統計數據- 歷史悠久且買主較不會質疑 

缺點：由於現今產品之Cycle time短，近幾年客戶端對IT類產品壽命要求須達五年也越來越多，因此試驗通常耗時較久，因此若以適當之溫度應力分析方法將可大幅縮短試驗之進行時程。

http://www.istgroup.com/chinese/3_service/03_01_detail.php?MID=2&SID=53&ID=149

可靠性管理

1. 可靠性乃探討整個產品壽命週期之特性，因此需從設計、製造、銷售、使用及報廢的整個週期加以管理。

2. 應從壽命週期成本分析的觀點來設計產品之可靠度。

3. 影響可靠度的因素，包括人、材料、製造方法、使用環境等，所以應從整體的系統環境來設計和管理可靠度。