錫銀銲錫與ENIG /Cu/Ni及OSP /Cu之界面反應研究

Abstract

隨著電子產品愈講究多功能及輕薄短小，致使電子封裝技術也必須與時並進。而在電子封裝中，當銲點與基材進行銲接時，銲料會與基材上的金屬發生化學反應，進而在界面生成一或多種介金屬，而這些介金屬對銲點的可靠度影響甚鉅。因此，欲提升銲點可靠度，就必須了解銲點與基材間界面反應之情形，且現今在電子封裝中最常使用表面處理層為OSP/Cu 與ENIG /Cu/Ni，由於環保意識的抬頭與經濟的考量 錫球中所使用的銲料也逐漸轉為無鉛製程。 本研究之主要目的即是探討無鉛錫銀與不同的基材表面處理墊層(Surface Finish)之治金反應。實驗內容分為三部分：一、銲錫球銲接後，進行高溫儲存測試，在150℃下，0 - 1000小時之固態時效處理，觀察經過不同的時效時間後，其界面之反應與銲點的強度變化。二、進行廻銲測試，頂溫是250℃，分別進行0 ~ 10 分鐘的廻銲，在廻銲過後觀察其反應結果的截面積，並且以掃描式電子顯微鏡觀察界面反應及介金屬化合物之生長行為，並利用推球機(Dage Series 4000 Bond Tester)在不同迴銲時間下測試其銲點的推力強度。三、試片施以高溫儲存、高加速壓力、壓力蒸煮等可靠度的加速試驗，藉由推力測試銲錫與不同的基材表面處理層基板間接合強度。 綜觀可靠度試驗後的強度結果:銲錫與OSP及ENIG均有好的銲錫性，兩種接點之強度均隨時效時間增加而降低。而下降幅度最大為壓力蒸煮鍋測試，OSP銲錫接點經不同環境條件試驗後之接點強度衰減幅度皆大於 ENIG墊層，比較ENIG與OSP銲墊的接著行為，ENIG銲錫接點有較佳抗衰敗能力。

With the miniaturization of modern electronic products and devices, the packaging density of components such as chips significantly increases, and the scale of interconnections becomes smaller and smaller. Consequently, the reliability of solder joints plays key roles. And understanding the volume effect of Snag solder on interfacial reaction will be critical in solder joint reliability. The OSP/Cu and ENIG /Cu/Ni surface finish is the most common and important for solder pad and bumps in industry now. In Flip-Chip packaging, lead-free solders are replacing traditional SnPb solders gradually due to environmental concern. The main objective of this proposal is then to study the reactions between such lead-free solders with different surface finish used in the industry. This study divides third parts. First part experiment : After reflow, the solder joints were subjected to thermal aging at 150 oC for time up to 1000 hrs. The bonding strengths of the solder joints with different thermal aging time were then tested. Second part experiment : For the reflow test, the peak reflow temperature was 250℃, and the reflow time was 0-10 minute. The research was to evaluate the reliability of the solder joints by measuring the bonding strength of the solder joints on the FCBGA substrates. Besides, we analyzed the fracture surface and cross-section view. The microstructureal analyses of samples and the composition of reaction product was identified by BEI .The measurements of bonding strength for solder joints were obtained using a Dage Series 4000 Bond Tester. Third part experiment : Reliability test including high temperature storage (HTS), high accelerated stress test (HAST) and pressure cooker test (PCT) were carried out to serve as accelerated tests .Die shear test was applied to study the bonding strength between SnAg solder and different surface finish. From the bonding strength results after reliability tests, the OSP/Cu and ENIG /Cu/Ni surface finish had good solderability. In the other hand, as thermal aging time increased, the bonding strength was decreased. The bonding strength decreased drastically after PCT test. The bonding strength of OSP solder joints is lower than ENIG solder joints.