FOX輕型石英晶體，美國(guó)?？怂构緫{借著精湛工藝打磨出高質(zhì)量的石英晶振，并因此一舉成名，成為當(dāng)下最受歡迎的元器件制造商之一，隨著行業(yè)的快速發(fā)展，?？怂构静粩鄡?yōu)化與迭代自身的產(chǎn)品，因而在市場(chǎng)上獲得更多的機(jī)會(huì)，為了更好滿足用戶的需求，對(duì)于產(chǎn)品極致的追求，使得FOX公司不斷突破自我，走向新的創(chuàng)新之路，也成就更加偉大的?？怂?。

石英晶體的“老化”導(dǎo)致頻率隨時(shí)間變化，可能必須采取這種影響由客戶在設(shè)計(jì)電路時(shí)考慮取決于需要實(shí)現(xiàn)。石英老化的主要原因有兩個(gè)晶體，一個(gè)是由于傳質(zhì)，另一個(gè)是因?yàn)閺?qiáng)調(diào).

質(zhì)量轉(zhuǎn)移

設(shè)備封裝內(nèi)的任何不希望的污染都可能將物質(zhì)轉(zhuǎn)移到晶體中或從晶體中轉(zhuǎn)移出來(lái)，導(dǎo)致將改變頻率的石英坯的質(zhì)量設(shè)備的。例如，用于安裝石英坯件會(huì)產(chǎn)生“排氣” 會(huì)在惰性氣體中產(chǎn)生氧化物質(zhì)密封的水晶包裝里的空氣生產(chǎn)過(guò)程必須得到很好的控制。理想情況下制造方法盡可能干凈，以消除任何效果并給出良好的老化結(jié)果。

強(qiáng)調(diào)
這可能發(fā)生在晶體的各個(gè)組件中從石英坯料的加工環(huán)氧樹(shù)脂安裝粘合劑，晶體安裝結(jié)構(gòu)以及器件中使用的金屬電極材料的類型。加熱和冷卻也會(huì)由于不同膨脹系數(shù)。系統(tǒng)中的應(yīng)力通常隨著系統(tǒng)放松而隨時(shí)間變化，這可能導(dǎo)致頻率的變化。
實(shí)踐中的老齡化
當(dāng)觀察晶體的示例老化測(cè)試結(jié)果時(shí)，可以看出，頻率的變化通常是在第一年最偉大，并隨著時(shí)間的推移而衰退。它必須然而，請(qǐng)注意，例如，如果指定了設(shè)備每年最大±5ppm；這并不意味著衰老5年后為±5ppm×5年，即±25ppm。在實(shí)踐中，示例的±5ppm老化裝置可能僅為±1ppm至運(yùn)行第一年±2ppm，然后減少隨后幾年。對(duì)于10年內(nèi)最大±10ppm的石英晶體諧振器老化，通常使用通用“指南”盡管在現(xiàn)實(shí)中它通常比這個(gè)要少得多。是的甚至無(wú)法預(yù)測(cè)設(shè)備的確切老化在同一時(shí)間由同一批石英將表現(xiàn)出略微不同的老化特性。
生產(chǎn)過(guò)程必須從零件到部分，來(lái)自石英坯料的制造，電極尺寸及其位置，用于安裝石英及其固化熱剖面，都有輕微影響在頻率上。設(shè)備可能老化為負(fù)或正取決于內(nèi)部原因一個(gè)批次往往遵循類似的結(jié)果。一般來(lái)說(shuō)在90%以上的制造零件中，老化效應(yīng)是負(fù)面的。

This can occur within various components of the crystal from the processing of the quartz blank, the curing of the epoxy mounting adhesive, the crystal mounting structure and the type of metal electrode material used in the device. Heating and cooling also causes stress due to different expansion coefficients. Stress in the system usually changes over time as the system relaxes and this can cause a change in frequency.

Ageing in practice

 When looking at example ageing test results of crystals, it can be seen that the change in frequency is generally greatest in the 1st year and decays away with time. It must be noted however that for example if a device is specified at ±5ppm max per year; it does not follow that the ageing after 5 yrs will be ±5ppm x 5yrs, i.e. ±25ppm. In practice, the example ±5ppm ageing device may be only ±1ppm to ±2ppm in the 1st year of operation and then reduces over subsequent years. It is common to use a general ‘guiderule’ for crystal ageing of ±10ppm max over 10 years although in reality it is usually much less than this. It is impossible to predict the exact ageing of a device as even parts made at the same time and from the same batch of quartz will exhibit slightly different ageing characteristics. The production process must be consistent from part to part, from the manufacture of the quartz blank, the electrode size and its placement, to the epoxy used to mount the quartz and its curing thermal profile, all have a slight affect on frequency. Devices can age negatively or positively depending upon the internal causes although parts from one batch tend to follow similar results. Generally the ageing effect is negative in over 90% of parts manufactured

Accelerated ageing 

It is common industry practice to use an accelerated ageing process to predict long term frequency movement by soaking devices at elevated temperatures and measuring frequency movement at relevant intervals. It is normal to test crystals using a passive test (i.e. non-powered). The general rule used is that soaking a crystal at +85°C for 30 days is equivalent to 1 year of ageing at normal room temperature. If this test is extended for enough time then the recorded data can be plotted graphically to enable via extrapolation, the prediction of future long term ageing.

Frequency adjustment 

Note that the ageing of quartz effectively changes the frequency tolerance of the crystal and does not directly influence the stability of the quartz over temperature to any great degree as this parameter is dictated by the ‘cutangle’ of the quartz used. If using quartz oscillators that have a voltage-control function such as VCXOs, TCXOs or OCXOs, the output frequency can be adjusted back to its nominally specified value.

The engineer designing a circuit using either a crystal or oscillator will generally know what overall stability figure their equipment must meet over a particular time period. As the tolerance and/or stability of a device decreases then the more important ageing becomes. For example using a TCXO at ±1ppm stability over temperature will require ageing to be kept to relatively small values. However, if the total frequency movement allowance of a design is for example ±200ppm and a device with a rating of ±100ppm is used then a small amount of ageing can effectively be ignored.