Introduction to PCB surface OSP treatment and chemical nickel gold

1 Introduction

Tin-lead has long played the role of protecting the copper surface and maintaining solderability. From molten tin to spray tin, decades have passed. Several insurmountable problems have been encountered, and alternative processes have to be used:

A. Pitch is too thin, causing bridging

B. The requirements for welding surface flatness are becoming stricter

C. COB (chip on board) boards are widely used in design

D. Environmental Pollution This chapter introduces the two most commonly used processes, OSP and chemical nickel-gold.

2 OSP

OSP is the abbreviation of Organic Solderability Preservatives, which is translated into organic solderability preservatives in Chinese, also known as copper preservatives, and Preflux in English. This chapter will call it copper preservatives.

2.1

Types and process introduction

A. BTA (Benzotriazole): BENZOTRIAZOLE

BTA is a white, light yellow, odorless, crystalline fine powder. It is very stable in acids and alkalis, and is not prone to redox reactions. It can form stable compounds with metals. ENTHON dissolves it in methanol and aqueous solutions and sells it as a copper surface antioxidant (TARNISH AND OXIDE RESIST). The trade names are CU-55 and CU-56. The copper surface treated with CU-56 can produce a protective film to prevent the bare copper from oxidizing rapidly. The operation process is shown in Table 14.1.

B. AI (Alkylimidazole) ALKYLIMIDAZOLE PREFLUX was developed by Shikoku Chemical Co., Ltd. in Japan, which used ALKYLIMIDAZOLE as a copper protectant. The patent was applied for in 1985 and it was used as an etching resist. However, it was not widely used because it was transparent and difficult to detect. GLICOAT was later introduced, which was derived from it.

GLICOAT-SMD(E3) has the following characteristics:

-Compatible with flux, maintaining good solderability

-Can withstand high heat soldering process

-Prevent copper surface from oxidation

C. ABI (Alkylbenzimidazole) ALKYLBENZIMIDZOLE

Developed by Japan's Sanhe Co., Ltd., the product name is CUCOAT A. It is a moisture-resistant copper protector. It can form a complex with copper atoms to prevent oxidation of the copper surface. It is compatible with all kinds of solder pastes and has a positive effect on solderability.

D. Currently, the following are representative manufacturers of related products on the market:

Acetic acid adjustment system:

GLICOAT-SMD (E3) OR (F1)

WPF-106A (TAMURA)

ENTEK 106A (ENTHON)

MEC CL-5708 (MEC)

MEC CL-5800(MEC)

Formic acid adjustment system:

SCHERCOAT CUCOAT A

KESTER

Most of the liquid medicine is heated to increase the growth rate, so the water evaporates quickly and the pH is difficult to control. When the pH is increased, MIDAZOLE will become insoluble and crystallize, so the pH must be adjusted back. Generally, acetic acid (ACETIC ACID) or formic acid (FORMIC ACID) is used to adjust.

2.2

Organic solderability films with a thickness of about 0.4 μm can achieve the purpose of multiple fusion welding. Although they are cheap and easy to operate, they have the following disadvantages:

A. OSP is transparent and difficult to measure and inspect visually

B. Too high film thickness is not conducive to low solid content, low activity no-clean solder paste operation, and Cu6Sn5 IMC that is conducive to welding is not easy to form

C. Multiple assemblies must be performed in a nitrogen environment

D. If partial gold plating is performed before OSP, the copper contained in the operating bath may be deposited on the gold, which may cause problems for some products.

E. OSP Rework must be done with extreme caution