PCB科技 - PCB板回流焊爆裂板的分析與改進

前言, 在裡面 PCB電路板 reflow welding analysis and 改進ment of burst plate

With the development of electronic 產品 in the direction of multi-function, 高密度, 小型化, 3維空間越來越多, 散熱的需求變得越來越重要. 同時, 許多資料的不同熱膨脹係數引起的熱應力和翹曲使裝配失敗的風險新增, 隨後電子產品早期失效的概率也會新增. 更大一點. 因此, PCB焊接可靠性變得越來越重要. 以下介紹了回流焊中的板件失效現象及其改進方法，供參考.

1 Plate burst phenomenon in reflow welding

1.1 Definition of burst board
Definition: In the process of reflow soldering (especially lead-free applications), the separation phenomenon that occurs between the PP layer 和 secondary layer (L2.) copper foil brown surface of the HDI 多層PCB during the second
compression, 我們將其定義為爆破板. 從切片分析, 板爆炸的位置發生在1-2層的密集埋區； 未發現碎片或其他异常； 切片顯示木板爆裂得非常厲害, 一些第二層電路被拉開.

1.2 Factors that affect the board burst

⑴ The formation source of volatile matter is a necessary condition for the 爆炸

1. Moisture absorption problem
The following shows that the existence of water in the PCB板, 水蒸氣擴散管道及水蒸氣壓力隨溫度的變化, 揭示水蒸汽的存在是PCB爆炸的主要原因. The
moisture in the PCB mainly exists in the resin molecules, as well as the macro-physical defects (such as voids, micro-cracks) inside the PCB板. The water absorption rate and equilibrium water absorption of epoxy resin are mainly determined by
the free volume and the concentration of polar groups. 自由體積越大, 初始吸水率越快, 極性基團對水有親和力, which is the main reason why epoxy resins have higher water
absorption. 極性基團的含量越大, 平衡吸水率越大. 總之, 環氧樹脂的初始吸水率由自由體積决定, while the equilibrium water absorption is determined
by the content of polar groups. 一方面, 溫度 PCB板 無鉛回流焊接期間新增, 這導致自由體積中的水和極性基團形成氫鍵, which can obtain enough
energy to diffuse in the resin. 水向外擴散並聚集在空隙或微裂紋中, 空隙中水的摩爾體積分數新增.

另一方面, 隨著焊接溫度的升高, 水的飽和蒸汽壓也會新增. The saturated vapor pressure of water vapor at 224°C is 2500kPa; the saturated vapor pressure of water vapor at 250°C is 4000kPa; and
when the welding temperature rises to 26.0°C, 水蒸汽的飽和蒸氣壓甚至達到5000kPa. 當資料層之間的結合强度低於水蒸汽產生的飽和蒸汽壓時, the
材料 bursts. 因此, 焊接前的吸濕是PCB分層和板爆裂的主要原因之一.

2. 儲存和生產過程中水分的影響. HDI多層PCB 是一種濕敏元件, PCB中的水對其效能有著極其重要的影響. For example:
(a) The moisture in the storage environment will cause significant changes in the characteristics of PP (prepreg);
(b) Without protection, PP很容易吸收水分. 圖1.3顯示了在30%的條件下儲存時PP的吸濕性, 50%, and 90% relative humidity; the relationship between the storage time and moisture
absorption rate of PP The relationship is obvious, 在靜態放置下隨著時間的推移, 混凝土的含水量 PCB板 將逐漸新增. The water absorption rate of vacuum packaging is higher than the water absorption
rate of no vacuum packaging, 吸水率隨暫存時間的新增而變化.
(c) Moisture mainly penetrates the interface between various substances in the resin system, 水對介面有影響.

3. Harm of moisture absorption
(a) Increase the volatile content of PP.
(b) The presence of moisture in the PP resin weakens the cross-linking between the resin molecules, 導致電路板各層之間的粘合力降低, 板的抗熱震性减弱. 多層板容易出現白點, 冒泡, 熱油或焊錫槽中的分層和熱風整平.

⑵ Poor adhesion between PP and copper foil is a sufficient condition for plate burst
1. Phenomenon description It can be seen from the slice analysis that the position of the plate burst is between the secondary pressing pp and the contact surface (browning surface) of the copper foil.
銅是一種金屬狀態的非極性物質, 囙此，許多粘合劑對銅箔的附著力很小. 如果銅箔表面未經處理, 即使使用性能優异的粘合劑, it will not have sufficient
adhesion and heat resistance. The early browning treatment method on the surface of copper foil was to form reddish-brown cuprous oxide (Cu2O) on the surface of the copper foil through chemical treatment. When it is bonded to a resin-
laminated substrate board, 雖然室溫下附著力新增, 剝落發生在200°C附近. 這是因為Cu2O對加熱不穩定，加熱後會從銅箔上脫落. 20世紀60年代, researchers at
Toshiba Corporation in Japan discovered that after treatment with a special chemical solution, the black velvet-like film (CuO) formed on the surface of the copper foil has finer crystals and can firmly adhere to the surface of the copper foil. The
stability is also very good, 這是後來常用的發黑過程. 20世紀90年代中期, Europe and the United States used a new type of browning process in which the inner conductive pattern of a new 多層 board was chemically
oxidized to replace the traditional blackening process, 在行業中得到了廣泛應用.

2. Mechanism of browning enhancing adhesion
The new browning process, its chemical reaction mechanism is: 2Cu + H2SO4 + H2O2 + nR1 + nR2 - CuSO4 + 2H2O + Cu(R1 + R2)
In the browning tank, 由於H2O2的微腐蝕效應, 基板銅的表面形成了不均勻的微觀結構, 囙此，可以獲得相當於未處理光滑銅表面6-7倍的結合面積. At the
same time, 在銅基板上沉積一層化學結合到銅基板表面的有機金屬薄膜, 基板銅表面的SEM影像呈棕色. And after the adhesive
enters the concave-convex part, 它還新增了機械嚙合效果.

3. Factors affecting the browning effect
The quality and effect of browning depend on the refinement of the process parameters control, such as:
(a) Choose a potion with advanced formula:
The browning layer with Atotech potion has a large roughness, 褐變層的結合力可以承受12倍的無鉛回流溫度而不會損壞電路板.
(b) Strengthen the monitoring of bath liquid composition during the production process.
(c) Browning (or black copper oxide) film thickness: Browning (or black copper oxide) film and PP bonding strength, 耐酸鹼性, 耐電暈性和耐高溫性與薄膜的結構和厚度有關 .
但並不是粘結强度越厚, 更高.
(d) Contaminated browning layer and process error: In the quality of a cracked plate, 剝下出現裂紋板的部分, 發現褐變層受到污染, and the resin was completely separated from the
contaminated browning layer.
層壓後，受污染零件的褐變層和pp板未能有效粘合, and the PCB板 在隨後的SMT組裝中起泡. 調查後, the high Tg 材料 was misused to press and solidify the
common 材料, 這也是外部銅箔和pp板之間粘合不良的原因之一.

⑶ Inappropriate selection of reflow temperature is the predisposing factor for plate burst
1. 溫度對中厚板爆裂的誘導作用. 通過分析平板破裂模式的充要條件, 可以知道，它們都是溫度的函數. The amount of volatile matter in the
multilayer board and its expansion pressure increase with the increase of the reflow soldering temperature, 而褐變層與聚丙烯之間的粘附力隨著溫度的升高而降低. 明顯地, the sufficient and
necessary conditions for the latent explosion board must be induced by the factor of temperature. Optimizing the reflow welding temperature curve based on the comprehensive analysis of specific product characteristics is effective in suppressing

the occurrence of plate bursting.
2. How to optimize the reflow soldering temperature according to product characteristics
(a) US Microelectronics Packaging CG Woychik pointed out: "Using normal SnPb alloy, 組件和 PCB板在回流焊接期間，s可以承受240攝氏度的溫度. When using SnAgCu (lead-free) alloy, JEDEC stipulates The
temperature is 260°C. 溫度升高可能危及電子封裝組件的完整性. 特別是對於許多層壓結構資料, 很容易導致層間分層, especially those new 材料
that contain more moisture. 內部含有水分. 再加上溫度的升高, most of the commonly used laminates (HDI多層 PCB板s) will have a large range of delamination."
(b) The American electronic assembly welding JSHwang also has this description in the book "Welding 材料 and processes in electronic assembly manufacturing": "Considering that the melting point temperature of existing lead-free 材料 is higher than that of SnPb eutectic 材料 Melting point temperature (183 degree Celsius), 為了在一定程度上降低回流焊接溫度, 合適的回流焊溫度分佈曲線尤為重要. He also
pointed out: According to the current production conditions, 如現有SMT製造商和基礎設施，設施包括組件和PCB的溫度特性, 等. The peak temperature of lead-free reflow
soldering should be maintained at 235°C. 綜合分析後, 在無鉛回流焊中 HDI多層PCB板s, 當合金化時使用SnAgCu焊料時, 建議將峰值溫度設定為235℃, not
exceeding 245°C. 實踐表明，採取這一措施後, 對平板破裂的抑制作用非常明顯.

–揮發性物質逸出不良是導致試驗失敗的一個因素 PCB板
從切片分析, 幾乎所有爆破板的位置都發生在埋孔上方覆蓋有大面積銅箔的部分.
這種設計的可製造性確實存在問題, mainly in the following aspects:
⑴ After the welding is heated, it is unfavorable for the emission of the volatile matter (such as moisture, 等.) accumulated in the buried hole and the interlayer;
⑵ Intensified the unevenness of the surface temperature distribution during reflow welding;
⑶ It is not conducive to eliminating the thermal stress in the welding process, 容易形成應力集中, 這加劇了 HDI多層PCB. 明顯地, 不合理的平面設計 HDI在無鉛製造過程中，多層板產品導致了板爆裂的發生.

1.3 The mechanism of board burst

⑴ The mechanism of plate explosion According to the above analysis and summary of the phenomenon of plate explosion, 我們可以根據以下物理模型研究和分析平板爆炸的物理過程.
1. 工作環境溫度不太高時, 多層板L1-L2之間的粘合良好.
2. 隨著加熱過程的進行, the volatile matter (including moisture) in the buried hole and the inner layer is continuously discharged.
3. The exhausted volatile gas accumulates between the buried hole and the PP (bonding sheet).
4. 隨著溫度持續上升, 越來越多的氣體聚集在埋藏的孔口附近, 形成較大的膨脹壓力, 這使得L2和PP的褐變表面受到一個膨脹力，將它們分開.
5. When the final expansion pressure is less than the adsorption force between the browning surface and the PP (f6. When the final expansion pressure is greater than the adsorption force between the browning surface and PP (f>F), 褐變面和PP沿L2分離, 如圖1所示.14 This kind of obvious lumpy bubbling
and stratification phenomenon. 當PCB被加熱時, 部分自由體積的水可能會通過微孔PCB基板流失, 從而减少可能積聚在空隙或微裂紋中的水的摩爾體積分數,
這有利於PCB的故障. improve. 然而, 如果PCB表面被大面積銅箔圖案覆蓋, 當PCB加熱時, the large copper foil surface above the buried hole blocks the water vapor that escapes
after heating, 這會新增微裂紋中的水蒸汽壓力, 導致發生斷板的幾率大大新增.

1.4 Countermeasures to prevent board explosion
⑴ Necessary conditions for eradicating plate explosion
The problem in PP storage is to prevent it from absorbing moisture. 空氣中的水分容易在PP上凝結，成為吸附水. 為了保持聚丙烯的原有效能不變, the more suitable storage
conditions are: temperature (10-20) degree Celsius, humidity <50%RH (stored in a vacuum). 據報導, 粘合片在5°C下存放一個月或一個月https://www.ipcb.com/pcb-board.html ger無法成功生產高品質的多層板, so refrigeration is not
advisable. 嚴格控制倉庫儲存條件 PCB板 products, 尤其是下雨天, increase the power of the dehumidifier to control the humidity in the warehouse; improve the packaging of PCB products used in the
lead-free process, and use vacuum film + aluminum film packaging to ensure Storage time and dryness; look for new 材料 with good heat resistance and low moisture absorption.

⑵ Sufficient conditions for suppressing the occurrence of board explosion: optimizing the quality of the "browning" process and increasing the adhesion between the internal layers of the PCB; selecting high-quality browning potions;
strengthening the monitoring of the quality of raw 材料, such as the resin content of PP 材料 (RC%), Resin gel time (GT), resin fluidity (RF%), volatile content (VC%) and other key indicators. 確保浸漬纖維空間中樹脂的均勻性和佔有率, 確保形成的基材吸水率低, 更好的介電效能, 良好的層間附著力和尺寸穩定性.

–改善大銅箔表面的透氣性. 根據以上對板塊爆炸位置特徵和板塊爆炸機理的分析. 明顯地, when the PCB surface has a large area of
copper foil layer design, 這將導致內部水蒸汽無法釋放, 囙此，有必要打開一個視窗，以改善表面上被大面積銅覆蓋的現象 PCB板 explosion.
優化回流焊的峰值溫度. 在保證良好潤濕的條件下, 盡可能降低回流的峰值溫度.